[Sitemap] [Contact] [Imprint] Deutsche Version Search site 

Atmospheric Chemistry and Physics - Current Research Articles



Current research articles: Atmospheric Chemistry

The author- or copyrights of the listed research articles below are held by the respective authors or site operators, who are also responsible for the content of the presentations.

More current articles from Chemistry Journals same topic: see the navigation menu on the left.

To list your article here please contact us by eMail.

To search this web page for specific words type "Ctrl" + "F" on your keyboard (Command + "F" on a Mac). Then: type the word you are searching for in the window that pops up!




On this page considered journals:



Atmospheric Chemistry and Physics - published by Copernicus Publications

ACP is an international scientific open access journal dedicated to the publication and public discussion of high quality studies investigating the Earth's atmosphere and the underlying chemical and physical processes. It covers the altitude range from the land and ocean surface up to the turbopause, including the troposphere, stratosphere and mesosphere.




Current articles of the journal:



On the relationship between the scattering phase function of cirrus and the atmospheric state

On the relationship between the scattering phase function of cirrus and the atmospheric state

Atmospheric Chemistry and Physics, 15, 1105-1127, 2015

Author(s): A. J. Baran, K. Furtado, L.-C. Labonnote, S. Havemann, J.-C. Thelen, and F. Marenco

This is the first paper to investigate the relationship between the shape of the scattering phase function of cirrus and the relative humidity with respect to ice (RHi, using space-based solar radiometric angle-dependent measurements. The relationship between RHi and the complexity of ice crystals has been previously studied using data from aircraft field campaigns and laboratory cloud chambers. However, to the best of our knowledge, there have been no studies to date that explore this relationship through the use of remotely sensed space-based angle-dependent solar radiometric measurements. In this paper, one case study of semi-transparent cirrus, which occurred on 25 January 2010 off the north-east coast of Scotland, is used to explore the possibility of such a relationship. Moreover, for the first time, RHi fields predicted by a high-resolution numerical weather prediction (NWP) model are combined with satellite retrievals of ice crystal complexity. The NWP model was initialised at midnight, on 25 January 2010, and the mid-latitude RHi field was extracted from the NWP model at 13:00 UTC. At about the same time, there was a PARASOL (Polarization and Anisotropy of Reflectance for Atmospheric science coupled with Observations from a Lidar) overpass, and the PARASOL swath covered the NWP-model-predicted RHi field. The cirrus case was located over Scotland and the North Sea. From the satellite channel based at 0.865 ?m, the directionally averaged and directional spherical albedos were retrieved between the scattering angles of about 80 and 130°. An ensemble model of cirrus ice crystals is used to predict phase functions that vary between phase functions that exhibit optical features (referred to as pristine) and featureless phase functions. For each of the PARASOL pixels, the phase function that best minimised differences between the spherical albedos was selected. This paper reports, for this one case study, an association between the most featureless phase function model and the highest values of NWP-predicted RHi (i.e. when RHi > 1.0). For pixels associated with NWP-model-predicted RHi < 1, it was impossible to generally discriminate between phase function models at the 5% significance level. It is also shown that the NWP model prediction of the vertical profile of RHi is in good agreement with dropsonde, in situ measurements and independent aircraft-based physical retrievals of RHi. Furthermore, the NWP model prediction of the cirrus cloud-top height and its vertical extent is also found to be in good agreement with aircraft-based lidar measurements.

Posted on 30 January 2015 | 12:00 am


Inclusion of mountain-wave-induced cooling for the formation of PSCs over the Antarctic Peninsula in a chemistry–climate model

Inclusion of mountain-wave-induced cooling for the formation of PSCs over the Antarctic Peninsula in a chemistry–climate model

Atmospheric Chemistry and Physics, 15, 1071-1086, 2015

Author(s): A. Orr, J. S. Hosking, L. Hoffmann, J. Keeble, S. M. Dean, H. K. Roscoe, N. L. Abraham, S. Vosper, and P. Braesicke

An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is from the temperature fluctuations induced by mountain waves. However, this formation mechanism is usually missing in chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate the representation of stratospheric mountain-wave-induced temperature fluctuations by the UK Met Office Unified Model (UM) at climate scale and mesoscale against Atmospheric Infrared Sounder satellite observations for three case studies over the Antarctic Peninsula. At a high horizontal resolution (4 km) the regional mesoscale configuration of the UM correctly simulates the magnitude, timing, and location of the measured temperature fluctuations. By comparison, at a low horizontal resolution (2.5° × 3.75°) the global climate configuration fails to resolve such disturbances. However, it is demonstrated that the temperature fluctuations computed by a mountain wave parameterisation scheme inserted into the climate configuration (which computes the temperature fluctuations due to unresolved mountain waves) are in relatively good agreement with the mesoscale configuration responses for two of the three case studies. The parameterisation was used to include the simulation of mountain-wave-induced PSCs in the global chemistry–climate configuration of the UM. A subsequent sensitivity study demonstrated that regional PSCs increased by up to 50% during July over the Antarctic Peninsula following the inclusion of the local mountain-wave-induced cooling phase.

Posted on 30 January 2015 | 12:00 am


Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model

Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model

Atmospheric Chemistry and Physics, 15, 1029-1070, 2015

Author(s): G. Katata, M. Chino, T. Kobayashi, H. Terada, M. Ota, H. Nagai, M. Kajino, R. Draxler, M. C. Hort, A. Malo, T. Torii, and Y. Sanada

Temporal variations in the amount of radionuclides released into the atmosphere during the Fukushima Daiichi Nuclear Power Station (FNPS1) accident and their atmospheric and marine dispersion are essential to evaluate the environmental impacts and resultant radiological doses to the public. In this paper, we estimate the detailed atmospheric releases during the accident using a reverse estimation method which calculates the release rates of radionuclides by comparing measurements of air concentration of a radionuclide or its dose rate in the environment with the ones calculated by atmospheric and oceanic transport, dispersion and deposition models. The atmospheric and oceanic models used are WSPEEDI-II (Worldwide version of System for Prediction of Environmental Emergency Dose Information) and SEA-GEARN-FDM (Finite difference oceanic dispersion model), both developed by the authors. A sophisticated deposition scheme, which deals with dry and fog-water depositions, cloud condensation nuclei (CCN) activation, and subsequent wet scavenging due to mixed-phase cloud microphysics (in-cloud scavenging) for radioactive iodine gas (I2 and CH3I) and other particles (CsI, Cs, and Te), was incorporated into WSPEEDI-II to improve the surface deposition calculations. The results revealed that the major releases of radionuclides due to the FNPS1 accident occurred in the following periods during March 2011: the afternoon of 12 March due to the wet venting and hydrogen explosion at Unit 1, midnight of 14 March when the SRV (safety relief valve) was opened three times at Unit 2, the morning and night of 15 March, and the morning of 16 March. According to the simulation results, the highest radioactive contamination areas around FNPS1 were created from 15 to 16 March by complicated interactions among rainfall, plume movements, and the temporal variation of release rates. The simulation by WSPEEDI-II using the new source term reproduced the local and regional patterns of cumulative surface deposition of total 131I and 137Cs and air dose rate obtained by airborne surveys. The new source term was also tested using three atmospheric dispersion models (Modèle Lagrangien de Dispersion de Particules d'ordre zéro: MLDP0, Hybrid Single Particle Lagrangian Integrated Trajectory Model: HYSPLIT, and Met Office's Numerical Atmospheric-dispersion Modelling Environment: NAME) for regional and global calculations, and the calculated results showed good agreement with observed air concentration and surface deposition of 137Cs in eastern Japan.

Posted on 30 January 2015 | 12:00 am


A regional carbon data assimilation system and its preliminary evaluation in East Asia

A regional carbon data assimilation system and its preliminary evaluation in East Asia

Atmospheric Chemistry and Physics, 15, 1087-1104, 2015

Author(s): Z. Peng, M. Zhang, X. Kou, X. Tian, and X. Ma

In order to optimize surface CO2 fluxes at grid scales, a regional surface CO2 flux inversion system (Carbon Flux Inversion system and Community Multi-scale Air Quality, CFI-CMAQ) has been developed by applying the ensemble Kalman filter (EnKF) to constrain the CO2 concentrations and applying the ensemble Kalman smoother (EnKS) to optimize the surface CO2 fluxes. The smoothing operator is associated with the atmospheric transport model to constitute a persistence dynamical model to forecast the surface CO2 flux scaling factors. In this implementation, the "signal-to-noise" problem can be avoided; plus, any useful observed information achieved by the current assimilation cycle can be transferred into the next assimilation cycle. Thus, the surface CO2 fluxes can be optimized as a whole at the grid scale in CFI-CMAQ. The performance of CFI-CMAQ was quantitatively evaluated through a set of Observing System Simulation Experiments (OSSEs) by assimilating CO2 retrievals from GOSAT (Greenhouse Gases Observing Satellite). The results showed that the CO2 concentration assimilation using EnKF could constrain the CO2 concentration effectively, illustrating that the simultaneous assimilation of CO2 concentrations can provide convincing CO2 initial analysis fields for CO2 flux inversion. In addition, the CO2 flux optimization using EnKS demonstrated that CFI-CMAQ could, in general, reproduce true fluxes at grid scales with acceptable bias. Two further sets of numerical experiments were conducted to investigate the sensitivities of the inflation factor of scaling factors and the smoother window. The results showed that the ability of CFI-CMAQ to optimize CO2 fluxes greatly relied on the choice of the inflation factor. However, the smoother window had a slight influence on the optimized results. CFI-CMAQ performed very well even with a short lag-window (e.g. 3 days).

Posted on 30 January 2015 | 12:00 am


Joint analysis of continental and regional background environments in the western Mediterranean: PM1 and PM10 concentrations and composition

Joint analysis of continental and regional background environments in the western Mediterranean: PM1 and PM10 concentrations and composition

Atmospheric Chemistry and Physics, 15, 1129-1145, 2015

Author(s): A. Ripoll, M. C. Minguillón, J. Pey, N. Pérez, X. Querol, and A. Alastuey

The complete chemical composition of atmospheric particulate matter (PM1 and PM10) from a continental (Montsec, MSC, 1570 m a.s.l.) and a regional (Montseny, MSY, 720 m a.s.l) background site in the western Mediterranean Basin (WMB) were jointly studied for the first time over a relatively long-term period (January 2010–March 2013).

Differences in average PMX concentration and composition between both sites were attributed to distance to anthropogenic sources, altitude, and different influence of atmospheric episodes. All these factors result in a continental-to-regional background increase of 4.0 ?g m?3 for PM10 and 1.1 ?g m?3 for PM1 in the WMB. This increase is mainly constituted by organic matter, sulfate, nitrate, and sea salt. However, higher mineral matter concentrations were measured at the continental background site owing to the higher influence of long-range transport of dust and dust resuspension.

Seasonal variations of aerosol chemical components were attributed to evolution of the planetary boundary layer (PBL) height throughout the year, variations in the air mass origin, and differences in meteorology. During warmer months, weak pressure gradients and elevated insolation generate recirculation of air masses and enhance the development of the PBL, causing the aging of aerosols and incrementing pollutant concentrations over a large area in the WMB, including the continental background. This is reflected in a more similar relative composition and absolute concentrations of continental and regional background aerosols. Nevertheless, during colder months the thermal inversions and the lower vertical development of the PBL leave MSC in the free troposphere most of the time, whereas MSY is more influenced by regional pollutants accumulated under winter anticyclonic conditions. This results in much lower concentrations of PMX components at the continental background site with respect to those at the regional background site.

The influence of certain atmospheric episodes caused different impacts at regional and continental scales. When long-range transport from central and eastern Europe and from north Africa occurs, the continental background site is frequently more influenced, thus indicating a preferential transport of pollutants at high altitude layers. Conversely, the regional background site was more influenced by regional processes.

Continental and regional aerosol chemical composition from the WMB revealed (a) high relevance of African dust transport and regional dust resuspension; (b) low biomass burning contribution; (c) high organic matter contribution; (d) low summer nitrate concentrations; and (e) high aerosol homogenization in summer.

Posted on 30 January 2015 | 12:00 am


Correlation slopes of GEM / CO, GEM / CO2, and GEM / CH4 and estimated mercury emissions in China, South Asia, the Indochinese Peninsula, and Central Asia derived from observations in northwestern and southwestern China

Correlation slopes of GEM / CO, GEM / CO2, and GEM / CH4 and estimated mercury emissions in China, South Asia, the Indochinese Peninsula, and Central Asia derived from observations in northwestern and southwestern China

Atmospheric Chemistry and Physics, 15, 1013-1028, 2015

Author(s): X. W. Fu, H. Zhang, C.-J. Lin, X. B. Feng, L. X. Zhou, and S. X. Fang

Correlation analyses between atmospheric mercury (Hg) and other trace gases are useful for identification of sources and constraining regional Hg emissions. Emissions of Hg in Asia contribute significantly to the global budget of atmospheric Hg. However, due to the lack of reliable data on the source strength, large uncertainties remain in the emission inventories of Hg in Asia. In the present study, we calculated the correlation slopes of GEM / CO, GEM / CO2, and GEM / CH4 for mainland China, South Asia, the Indochinese Peninsula, and Central Asia using the ground-based observations at three remote sites in northwestern and southwestern China, and applied these values to estimate GEM emissions in the four source regions. The geometric mean GEM / CO correlation slopes for mainland China, South Asia, the Indochinese Peninsula, and Central Asia were 7.3 ± 4.3, 7.8 ± 6.4, 7.8 ± 5.0, and 13.4 ± 9.5 pg m?3 ppb?1, respectively, and values in the same source regions were 33.3 ± 30.4, 27.4 ± 31.0, 23.5 ± 15.3, and 20.5 ± 10.0 pg m?3 ppb?1 for the GEM / CH4 correlation slopes, respectively. The geometric means of GEM / CO2 correlation slopes for mainland China, South Asia, and Central Asia were 240 ± 119, 278 ± 164, 315 ± 289 pg m?3 ppm?1, respectively. These values were the first reported correlation slopes of GEM / CO, GEM / CO2, and GEM / CH4 in four important source regions of Asia, not including the GEM / CO ratios in mainland China. The correlation slopes of GEM / CO, GEM / CO2, and GEM / CH4 in Asia were relatively higher than those observed in Europe, North America, and South Africa, which may highlight GEM emissions from non-ferrous smelting, large-scale and artisanal mercury and gold production, natural sources, and historically deposited mercury (re-emission) in Asia. Using the observed GEM / CO and GEM / CO2 slopes, and the recently reported emission inventories of CO and CO2, the annual GEM emissions in mainland China, South Asia, the Indochinese Peninsula, and Central Asia were estimated to be in the ranges of 1071–1187, 340–470, 125, and 54–90 t, respectively. The estimated quantity of GEM emissions from the GEM / CH4 correlation slopes is significantly larger, which may be due to the larger uncertainties in CH4 emissions in Asia as well as insufficient observations of GEM / CH4 correlation slopes, therefore leading to an overestimate of GEM emissions. Our estimates of GEM emissions in the four Asian regions were significantly higher (3–4 times) than the anthropogenic GEM emissions reported in recent studies. This discrepancy could come from a combination of reasons including underestimates of anthropogenic and natural GEM emissions; large uncertainties related to CO, CO2, and CH4 emission inventories; and inherent limitations of the correlation slope method.

Posted on 29 January 2015 | 12:00 am


Secondary organic aerosol formation from hydroxyl radical oxidation and ozonolysis of monoterpenes

Secondary organic aerosol formation from hydroxyl radical oxidation and ozonolysis of monoterpenes

Atmospheric Chemistry and Physics, 15, 991-1012, 2015

Author(s): D. F. Zhao, M. Kaminski, P. Schlag, H. Fuchs, I.-H. Acir, B. Bohn, R. Häseler, A. Kiendler-Scharr, F. Rohrer, R. Tillmann, M. J. Wang, R. Wegener, J. Wildt, A. Wahner, and Th. F. Mentel

Oxidation by hydroxyl radical (OH) and ozonolysis are the two major pathways of daytime biogenic volatile organic compound (BVOC) oxidation and secondary organic aerosol (SOA) formation. In this study, we investigated the particle formation of several common monoterpenes (?-pinene, ?-pinene and limonene) by OH-dominated oxidation, which has seldom been investigated. OH oxidation experiments were carried out in the SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction) chamber in Jülich, Germany, at low NOx (0.01 ~ 1 ppbV) and low ozone (O3) concentration (< 20 ppbV). OH concentration and total OH reactivity (kOH) were measured directly, and through this the overall reaction rate of total organics with OH in each reaction system was quantified. Multi-generation reaction process, particle growth, new particle formation (NPF), particle yield and chemical composition were analyzed and compared with that of monoterpene ozonolysis. Multi-generation products were found to be important in OH-dominated SOA formation. The relative role of functionalization and fragmentation in the reaction process of OH oxidation was analyzed by examining the particle mass and the particle size as a function of OH dose. We developed a novel method which quantitatively links particle growth to the reaction rate of OH with total organics in a reaction system. This method was also used to analyze the evolution of functionalization and fragmentation of organics in the particle formation by OH oxidation. It shows that functionalization of organics was dominant in the beginning of the reaction (within two lifetimes of the monoterpene) and fragmentation started to play an important role after that. We compared particle formation from OH oxidation with that from pure ozonolysis. In individual experiments, growth rates of the particle size did not necessarily correlate with the reaction rate of monoterpene with OH and O3. Comparing the size growth rates at the similar reaction rates of monoterpene with OH or O3 indicates that, generally, OH oxidation and ozonolysis had similar efficiency in particle growth. The SOA yield of α-pinene and limonene by ozonolysis was higher than that of OH oxidation. Aerosol mass spectrometry (AMS) shows SOA elemental composition from OH oxidation follows a slope shallower than ?1 in the O / C vs. H / C diagram, also known as Van Krevelen diagram, indicating that oxidation proceeds without significant loss of hydrogen. SOA from OH oxidation had higher H / C ratios than SOA from ozonolysis. In ozonolysis, a process with significant hydrogen loss seemed to play an important role in SOA formation.

Posted on 28 January 2015 | 12:00 am


Influence of aerosol chemical composition on N2O5 uptake: airborne regional measurements in northwestern Europe

Influence of aerosol chemical composition on N2O5 uptake: airborne regional measurements in northwestern Europe

Atmospheric Chemistry and Physics, 15, 973-990, 2015

Author(s): W. T. Morgan, B. Ouyang, J. D. Allan, E. Aruffo, P. Di Carlo, O. J. Kennedy, D. Lowe, M. J. Flynn, P. D. Rosenberg, P. I. Williams, R. Jones, G. B. McFiggans, and H. Coe

Aerosol chemical composition was found to influence nighttime atmospheric chemistry during a series of airborne measurements in northwestern Europe in summer conditions, which has implications for regional air quality and climate. The uptake of dinitrogen pentoxide, γ (N2O5), to particle surfaces was found to be modulated by the amount of water content and ammonium nitrate present in the aerosol. The conditions prevalent in this study suggest that the net uptake rate of N2O5 to atmospheric aerosols was relatively efficient compared to previous studies, with γ (N2O5) values in the range 0.01–0.03. This is likely a consequence of the elevated relative humidity in the region, which promotes greater aerosol water content. Increased nitrate concentrations relative to particulate water were found to suppress N2O5 uptake. The results presented here contrast with previous ambient studies of N2O5 uptake, which have generally taken place in low-nitrate environments in the USA. Comparison of the N2O5 uptake derived from the measurements with a parameterised scheme that is based on the ratio of particulate water to nitrate yielded reasonably good agreement in terms of the magnitude and variation in uptake, provided the effect of chloride was neglected. An additional suppression of the parameterised uptake is likely required to fully capture the variation in N2O5 uptake, which could be achieved via the known suppression by organic aerosol. However, existing parameterisations representing the suppression by organic aerosol were unable to fully represent the variation in N2O5 uptake. These results provide important ambient measurement constraint on our ability to predict N2O5 uptake in regional and global aerosol models. N2O5 uptake is a potentially important source of nitrate aerosol and a sink of the nitrate radical, which is the main nocturnal oxidant in the atmosphere. The results further highlight the importance of ammonium nitrate in northwestern Europe as a key component of atmospheric composition in the region.

Posted on 28 January 2015 | 12:00 am


Atmospheric wet and dry deposition of trace elements at 10 sites in Northern China

Atmospheric wet and dry deposition of trace elements at 10 sites in Northern China

Atmospheric Chemistry and Physics, 15, 951-972, 2015

Author(s): Y. P. Pan and Y. S. Wang

Atmospheric deposition is considered to be a major process that removes pollutants from the atmosphere and an important source of nutrients and contaminants for ecosystems. Trace elements (TEs), especially toxic metals deposited on plants and into soil or water, can cause substantial damage to the environment and human health due to their transfer and accumulation in food chains. Despite public concerns, quantitative knowledge of metal deposition from the atmosphere to ecosystems remains scarce. To advance our understanding of the spatiotemporal variations in the magnitudes, pathways, compositions and impacts of atmospherically deposited TEs, precipitation (rain and snow) and dry-deposited particles were collected simultaneously at 10 sites in Northern China from December 2007 to November 2010.

The measurements showed that the wet and dry depositions of TEs in the target areas were orders of magnitude higher than previous observations within and outside China, generating great concern over the potential risks. The spatial distribution of the total (wet plus dry) deposition flux was consistent with that of the dry deposition, with a significant decrease from industrial and urban areas to suburban, agricultural and rural sites, while the wet deposition exhibited less spatial variation. In addition, the seasonal variation of wet deposition was also different from that of dry deposition, although they were both governed by the precipitation and emission patterns.

For the majority of TEs that exist as coarse particles, dry deposition dominated the total flux at each site. This was not the case for potassium, nickel, arsenic, lead, zinc, cadmium, selenium, silver and thallium, for which the relative importance between wet and dry deposition fluxes varied by site. Whether wet deposition is the major atmospheric cleansing mechanism for the TEs depends on the size distribution of the particles.

We found that atmospheric inputs of copper, lead, zinc, cadmium, arsenic and selenium were of the same magnitude as their increases in the topsoil of agricultural systems. At a background forest site in Northern China, the total deposition flux of lead observed in this study (14.1 mg m?2 yr−1) was twice that of the critical load calculated for temperate forest ecosystems in Europe. These findings provide baseline data needed for future targeting policies to protect various ecosystems from long-term heavy metal input via atmospheric deposition.

Posted on 28 January 2015 | 12:00 am


Satellite observations of cirrus clouds in the Northern Hemisphere lowermost stratosphere

Satellite observations of cirrus clouds in the Northern Hemisphere lowermost stratosphere

Atmospheric Chemistry and Physics, 15, 927-950, 2015

Author(s): R. Spang, G. Günther, M. Riese, L. Hoffmann, R. Müller, and S. Griessbach

Here we present observations of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) of cirrus cloud and water vapour in August 1997 in the upper troposphere and lower stratosphere (UTLS). The observations indicate a considerable flux of moisture from the upper tropical troposphere into the extratropical lowermost stratosphere (LMS), resulting in the occurrence of high-altitude optically thin cirrus clouds in the LMS.

The locations of the LMS cloud events observed by CRISTA are consistent with the tropopause height determined from coinciding radiosonde data. For a hemispheric analysis in tropopause relative coordinates an improved tropopause determination has been applied to the European Centre for Medium-Range Weather Forecasts (ECMWF) temperature profiles. We found that a significant fraction of the cloud occurrences in the tropopause region are located in the LMS, even if a conservative overestimate of the cloud top height (CTH) determination by CRISTA of 500 m is assumed. The results show rather high occurrence frequencies (~ 5%) up to high northern latitudes (70° N) and altitudes well above the tropopause (> 500 m at ~350 K and above) in large areas at mid- and high latitudes.

Comparisons with model runs of the Chemical Lagrangian Model of the Stratosphere (CLaMS) over the CRISTA period show a reasonable consistency in the retrieved cloud pattern. For this purpose a limb ray tracing approach was applied through the 3-D model fields to obtain integrated measurement information through the atmosphere along the limb path of the instrument. The simplified cirrus scheme implemented in CLaMS seems to cause a systematic underestimation in the CTH occurrence frequencies in the LMS with respect to the observations. The observations together with the model results demonstrate the importance of isentropic, quasi-horizontal transport of water vapour from the subtropics and the potential for the occurrence of cirrus clouds in the lowermost stratosphere and tropopause region.

Posted on 27 January 2015 | 12:00 am


Macroscopic impacts of cloud and precipitation processes on maritime shallow convection as simulated by a large eddy simulation model with bin microphysics

Macroscopic impacts of cloud and precipitation processes on maritime shallow convection as simulated by a large eddy simulation model with bin microphysics

Atmospheric Chemistry and Physics, 15, 913-926, 2015

Author(s): W. W. Grabowski, L.-P. Wang, and T. V. Prabha

This paper discusses impacts of cloud and precipitation processes on macrophysical properties of shallow convective clouds as simulated by a large eddy model applying warm-rain bin microphysics. Simulations with and without collision–coalescence are considered with cloud condensation nuclei (CCN) concentrations of 30, 60, 120, and 240 mg?1. Simulations with collision–coalescence include either the standard gravitational collision kernel or a novel kernel that includes enhancements due to the small-scale cloud turbulence. Simulations with droplet collisions were discussed in Wyszogrodzki et al. (2013) focusing on the impact of the turbulent collision kernel. The current paper expands that analysis and puts model results in the context of previous studies. Despite a significant increase of the drizzle/rain with the decrease of CCN concentration, enhanced by the effects of the small-scale turbulence, impacts on the macroscopic cloud field characteristics are relatively minor. Model results show a systematic shift in the cloud-top height distributions, with an increasing contribution of deeper clouds for stronger precipitating cases. We show that this is consistent with the explanation suggested in Wyszogrodzki et al. (2013); namely, the increase of drizzle/rain leads to a more efficient condensate offloading in the upper parts of the cloud field. A second effect involves suppression of the cloud droplet evaporation near cloud edges in low-CCN simulations, as documented in previous studies (e.g., Xue and Feingold, 2006). We pose the question whether the effects of cloud turbulence on drizzle/rain formation in shallow cumuli can be corroborated by remote sensing observations, for instance, from space. Although a clear signal is extracted from model results, we argue that the answer is negative due to uncertainties caused by the temporal variability of the shallow convective cloud field, sampling and spatial resolution of the satellite data, and overall accuracy of remote sensing retrievals.

Posted on 27 January 2015 | 12:00 am


Influence of local air pollution on the deposition of peroxyacetyl nitrate to a nutrient-poor natural grassland ecosystem

Influence of local air pollution on the deposition of peroxyacetyl nitrate to a nutrient-poor natural grassland ecosystem

Atmospheric Chemistry and Physics, 15, 899-911, 2015

Author(s): A. Moravek, P. Stella, T. Foken, and I. Trebs

Dry deposition of peroxyacetyl nitrate (PAN) is known to have a phytotoxic impact on plants under photochemical smog conditions, but it may also lead to higher productivity and threaten species richness of vulnerable ecosystems in remote regions. However, underlying mechanisms or controlling factors for PAN deposition are not well understood and studies on dry deposition of PAN are limited. In this study, we investigate the impact of PAN deposition on a nutrient-poor natural grassland ecosystem situated at the edge of an urban and industrialized region in Germany. PAN mixing ratios were measured within a 3.5 months summer to early autumn period. In addition, PAN fluxes were determined with the modified Bowen ratio technique for a selected period. The evaluation of both stomatal and non-stomatal deposition pathways was used to model PAN deposition over the entire summer–autumn period. We found that air masses at the site were influenced by two contrasting pollution regimes, which led to median diurnal PAN mixing ratios ranging between 50 and 300 ppt during unpolluted and between 200 and 600 ppt during polluted episodes. The measured PAN fluxes showed a clear diurnal cycle with maximal deposition fluxes of ~?0.1 nmol m?2 s?1 (corresponding to a deposition velocity of 0.3 cm s−1) during daytime and a significant non-stomatal contribution was found. The ratio of PAN to ozone deposition velocities was found to be ~0.1, which is much larger than assumed by current deposition models. The modelled PAN flux over the entire period revealed that PAN deposition over an entire day was 333 ?g m?2 d?1 under unpolluted and 518 ?g m?2 d?1 under polluted episodes. Additionally, thermochemical decomposition PAN deposition accounted for 32% under unpolluted episodes and 22% under polluted episodes of the total atmospheric PAN loss. However, the impact of PAN deposition as a nitrogen source to the nutrient-poor grassland was estimated to be only minor, under both unpolluted and polluted episodes.

Posted on 26 January 2015 | 12:00 am


Aging of secondary organic aerosol generated from the ozonolysis of ?-pinene: effects of ozone, light and temperature

Aging of secondary organic aerosol generated from the ozonolysis of ?-pinene: effects of ozone, light and temperature

Atmospheric Chemistry and Physics, 15, 883-897, 2015

Author(s): C. Denjean, P. Formenti, B. Picquet-Varrault, M. Camredon, E. Pangui, P. Zapf, Y. Katrib, C. Giorio, A. Tapparo, B. Temime-Roussel, A. Monod, B. Aumont, and J. F. Doussin

A series of experiments was conducted in the CESAM (French acronym for Experimental Multiphasic Atmospheric Simulation Chamber) simulation chamber to investigate the evolution of the physical and chemical properties of secondary organic aerosols (SOAs) during different forcings. The present experiments represent a first attempt to comprehensively investigate the influence of oxidative processing, photochemistry, and diurnal temperature cycling upon SOA properties. SOAs generated from the ozonolysis of ?-pinene were exposed under dry conditions (< 1% relative humidity) to (1) elevated ozone concentrations, (2) light (under controlled temperature conditions) or (3) light and heat (6 °C light-induced temperature increase), and the resultant changes in SOA optical properties (i.e. absorption and scattering), hygroscopicity and chemical composition were measured using a suite of instrumentation interfaced to the CESAM chamber. The complex refractive index (CRI) was derived from integrated nephelometer measurements of 525 nm wavelength, using Mie scattering calculations and measured number size distributions. The particle size growth factor (GF) was measured with a hygroscopic tandem differential mobility analyzer (H-TDMA). An aerosol mass spectrometer (AMS) was used for the determination of the f44 / f43 and O : C ratio of the particles bulk.

No change in SOA size or chemical composition was observed during O3 and light exposure at constant temperature; in addition, GF and CRI of the SOA remained constant with forcing. On the contrary, illumination of SOAs in the absence of temperature control led to an increase in the real part of the CRI from 1.35 (±0.03) to 1.49 (±0.03), an increase of the GF from 1.04 (±0.02) to 1.14 (±0.02) and an increase of the f44 / f43 ratio from 1.73 (±0.03) to 2.23 (±0.03). The simulation of the experiments using the master chemical mechanism (MCM) and the Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) shows that these changes resulted from the evaporation of semi-volatile and less oxidized SOA species induced by the relatively minor increases in temperature (~ 6 °C). These surprising results suggest that ?-pinene–O3 SOA properties may be governed more by local temperature fluctuations than by oxidative processing and photochemistry.

Posted on 26 January 2015 | 12:00 am


Sunset–sunrise difference in solar occultation ozone measurements (SAGE II, HALOE, and ACE–FTS) and its relationship to tidal vertical winds

Sunset–sunrise difference in solar occultation ozone measurements (SAGE II, HALOE, and ACE–FTS) and its relationship to tidal vertical winds

Atmospheric Chemistry and Physics, 15, 829-843, 2015

Author(s): T. Sakazaki, M. Shiotani, M. Suzuki, D. Kinnison, J. M. Zawodny, M. McHugh, and K. A. Walker

This paper contains a comprehensive investigation of the sunset–sunrise difference (SSD, i.e., the sunset-minus-sunrise value) of the ozone mixing ratio in the latitude range of 10° S–10° N. SSD values were determined from solar occultation measurements based on data obtained from the Stratospheric Aerosol and Gas Experiment (SAGE) II, the Halogen Occultation Experiment (HALOE), and the Atmospheric Chemistry Experiment–Fourier transform spectrometer (ACE–FTS). The SSD was negative at altitudes of 20–30 km (?0.1 ppmv at 25 km) and positive at 30–50 km (+0.2 ppmv at 40–45 km) for HALOE and ACE–FTS data. SAGE II data also showed a qualitatively similar result, although the SSD in the upper stratosphere was 2 times larger than those derived from the other data sets. On the basis of an analysis of data from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) and a nudged chemical transport model (the specified dynamics version of the Whole Atmosphere Community Climate Model: SD–WACCM), we conclude that the SSD can be explained by diurnal variations in the ozone concentration, particularly those caused by vertical transport by the atmospheric tidal winds. All data sets showed significant seasonal variations in the SSD; the SSD in the upper stratosphere is greatest from December through February, while that in the lower stratosphere reaches a maximum twice: during the periods March–April and September–October. Based on an analysis of SD–WACCM results, we found that these seasonal variations follow those associated with the tidal vertical winds.

Posted on 23 January 2015 | 12:00 am


A comparison of HONO budgets for two measurement heights at a field station within the boreal forest in Finland

A comparison of HONO budgets for two measurement heights at a field station within the boreal forest in Finland

Atmospheric Chemistry and Physics, 15, 799-813, 2015

Author(s): R. Oswald, M. Ermel, K. Hens, A. Novelli, H. G. Ouwersloot, P. Paasonen, T. Petäjä, M. Sipilä, P. Keronen, J. Bäck, R. Königstedt, Z. Hosaynali Beygi, H. Fischer, B. Bohn, D. Kubistin, H. Harder, M. Martinez, J. Williams, T. Hoffmann, I. Trebs, and M. Sörgel

Atmospheric concentrations of nitrous acid (HONO), one of the major precursors of the hydroxyl radical (OH) in the troposphere, significantly exceed the values predicted by the assumption of a photostationary state (PSS) during daytime. Therefore, additional sources of HONO were intensively investigated in the last decades. This study presents budget calculations of HONO based on simultaneous measurements of all relevant species, including HONO and OH at two different measurement heights, i.e. 1 m above the ground and about 2 to 3 m above the canopy (24 m above the ground), conducted in a boreal forest environment. We observed mean HONO concentrations of about 6.5 × 108 molecules cm?3 (26 ppt) during daytime, more than 20 times higher than expected from the PSS of 0.2 × 108 molecules cm?3 (1 ppt). To close the budgets at both heights, a strong additional source term during daytime is required. This unidentified source is at its maximum at noon (up to 1.1 × 106 molecules cm?3 s?1, 160 ppt h−1) and in general up to 2.3 times stronger above the canopy than close to the ground. The insignificance of known gas phase reactions and other processes like dry deposition or advection compared to the photolytic decomposition of HONO at this measurement site was an ideal prerequisite to study possible correlations of this unknown term to proposed HONO sources. But neither the proposed emissions from soils nor the proposed photolysis of adsorbed HNO3 contributed substantially to the unknown source. However, the unknown source was found to be perfectly correlated to the unbalanced photolytic loss of HONO.

Posted on 23 January 2015 | 12:00 am


Tropospheric vertical column densities of NO2 over managed dryland ecosystems (Xinjiang, China): MAX-DOAS measurements vs. 3-D dispersion model simulations based on laboratory-derived NO emission from soil samples

Tropospheric vertical column densities of NO2 over managed dryland ecosystems (Xinjiang, China): MAX-DOAS measurements vs. 3-D dispersion model simulations based on laboratory-derived NO emission from soil samples

Atmospheric Chemistry and Physics, 15, 867-882, 2015

Author(s): B. Mamtimin, T. Behrendt, M. M. Badawy, T. Wagner, Y. Qi, Z. Wu, and F. X. Meixner

We report on MAX-DOAS observations of NO2 over an oasis–ecotone–desert ecosystem in NW China. There, local ambient NO2 concentrations originate from enhanced biogenic NO emission of intensively managed soils. Our target oasis "Milan" is located at the southern edge of the Taklimakan desert, very remote and well isolated from other potential anthropogenic and biogenic NOx sources. Four observation sites for MAX-DOAS measurements were selected, at the oasis centre, downwind and upwind of the oasis, and in the desert. Biogenic NO emissions in terms of (i) soil moisture and (ii) soil temperature of Milan oasis (iii) different land-cover type sub-units (cotton, Jujube trees, cotton/Jujube mixture, desert) were quantified by laboratory incubation of corresponding soil samples. Net potential NO fluxes were up-scaled to oasis scale by areal distribution and classification of land-cover types derived from satellite images using GIS techniques. A Lagrangian dispersion model (LASAT, Lagrangian Simulation of Aerosol Transport) was used to calculate the dispersion of soil emitted NO into the atmospheric boundary layer over Milan oasis. Three-dimensional (3-D) NO concentrations (30 m horizontal resolution) have been converted to 3-D NO2 concentrations, assuming photostationary state conditions. NO2 column densities were simulated by suitable vertical integration of modelled 3-D NO2 concentrations at those downwind and upwind locations, where the MAX-DOAS measurements were performed. Downwind–upwind differences (a direct measure of Milan oasis' contribution to the areal increase of ambient NO2 concentration) of measured and simulated slant (as well as vertical) NO2 column densities show excellent agreement. This agreement is considered as the first successful attempt to prove the validity of the chosen approach to up-scale laboratory-derived biogenic NO fluxes to ecosystem field conditions, i.e. from the spatial scale of a soil sample (cm2) to the size of an entire agricultural ecosystem (km2).

Posted on 23 January 2015 | 12:00 am


A comparison of four receptor models used to quantify the boreal wildfire smoke contribution to surface PM2.5 in Halifax, Nova Scotia during the BORTAS-B experiment

A comparison of four receptor models used to quantify the boreal wildfire smoke contribution to surface PM2.5 in Halifax, Nova Scotia during the BORTAS-B experiment

Atmospheric Chemistry and Physics, 15, 815-827, 2015

Author(s): M. D. Gibson, J. Haelssig, J. R. Pierce, M. Parrington, J. E. Franklin, J. T. Hopper, Z. Li, and T. J. Ward

This paper presents a quantitative comparison of the four most commonly used receptor models, namely absolute principal component scores (APCS), pragmatic mass closure (PMC), chemical mass balance (CMB) and positive matrix factorization (PMF). The models were used to predict the contributions of a wide variety of sources to PM2.5 mass in Halifax, Nova Scotia during the experiment to quantify the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS). However, particular emphasis was placed on the capacity of the models to predict the boreal wildfire smoke contributions during the BORTAS experiment. The performance of the four receptor models was assessed on their ability to predict the observed PM2.5 with an R2 close to 1, an intercept close to zero, a low bias and low RSME. Using PMF, a new woodsmoke enrichment factor of 52 was estimated for use in the PMC receptor model. The results indicate that the APCS and PMC receptor models were not able to accurately resolve total PM2.5 mass concentrations below 2 ?g m?3. CMB was better able to resolve these low PM2.5 concentrations, but it could not be run on 9 of the 45 days of PM2.5 samples. PMF was found to be the most robust of the four models since it was able to resolve PM2.5 mass below 2 ?g m?3, predict PM2.5 mass on all 45 days and utilise an unambiguous woodsmoke chemical tracer. The median woodsmoke relative contributions to PM2.5 estimated using PMC, APCS, CMB and PMF were found to be 0.08, 0.09, 3.59 and 0.14 ?g m?3 respectively. The contribution predicted by the CMB model seemed to be clearly too high based on other observations. The use of levoglucosan as a tracer for woodsmoke was found to be vital for identifying this source.

Posted on 23 January 2015 | 12:00 am


Characterization of biomass burning emissions from cooking fires, peat, crop residue, and other fuels with high-resolution proton-transfer-reaction time-of-flight mass spectrometry

Characterization of biomass burning emissions from cooking fires, peat, crop residue, and other fuels with high-resolution proton-transfer-reaction time-of-flight mass spectrometry

Atmospheric Chemistry and Physics, 15, 845-865, 2015

Author(s): C. E. Stockwell, P. R. Veres, J. Williams, and R. J. Yokelson

We deployed a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) to measure biomass-burning emissions from peat, crop residue, cooking fires, and many other fire types during the fourth Fire Lab at Missoula Experiment (FLAME-4) laboratory campaign. A combination of gas standard calibrations and composition sensitive, mass-dependent calibration curves was applied to quantify gas-phase non-methane organic compounds (NMOCs) observed in the complex mixture of fire emissions. We used several approaches to assign the best identities to most major "exact masses", including many high molecular mass species. Using these methods, approximately 80–96% of the total NMOC mass detected by the PTR-TOF-MS and Fourier transform infrared (FTIR) spectroscopy was positively or tentatively identified for major fuel types. We report data for many rarely measured or previously unmeasured emissions in several compound classes including aromatic hydrocarbons, phenolic compounds, and furans; many of these are suspected secondary organic aerosol precursors. A large set of new emission factors (EFs) for a range of globally significant biomass fuels is presented. Measurements show that oxygenated NMOCs accounted for the largest fraction of emissions of all compound classes. In a brief study of various traditional and advanced cooking methods, the EFs for these emissions groups were greatest for open three-stone cooking in comparison to their more advanced counterparts. Several little-studied nitrogen-containing organic compounds were detected from many fuel types, that together accounted for 0.1–8.7% of the fuel nitrogen, and some may play a role in new particle formation.

Posted on 23 January 2015 | 12:00 am


Model calculations of the effects of present and future emissions of air pollutants from shipping in the Baltic Sea and the North Sea

Model calculations of the effects of present and future emissions of air pollutants from shipping in the Baltic Sea and the North Sea

Atmospheric Chemistry and Physics, 15, 783-798, 2015

Author(s): J. E. Jonson, J. P. Jalkanen, L. Johansson, M. Gauss, and H. A. C. Denier van der Gon

Land-based emissions of air pollutants in Europe have steadily decreased over the past two decades, and this decrease is expected to continue. Within the same time span emissions from shipping have increased in EU ports and in the Baltic Sea and the North Sea, defined as SECAs (sulfur emission control areas), although recently sulfur emissions, and subsequently particle emissions, have decreased. The maximum allowed sulfur content in marine fuels in EU ports is now 0.1%, as required by the European Union sulfur directive. In the SECAs the maximum fuel content of sulfur is currently 1% (the global average is about 2.4%). This will be reduced to 0.1% from 2015, following the new International Maritime Organization (IMO) rules.

In order to assess the effects of ship emissions in and around the Baltic Sea and the North Sea, regional model calculations with the EMEP air pollution model have been made on a 1/4° longitude × 1/8° latitude resolution, using ship emissions in the Baltic Sea and the North Sea that are based on accurate ship positioning data. The effects on depositions and air pollution and the resulting number of years of life lost (YOLLs) have been calculated by comparing model calculations with and without ship emissions in the two sea areas. In 2010 stricter regulations for sulfur emissions were implemented in the two sea areas, reducing the maximum sulfur content allowed in marine fuels from 1.5 to 1%. In addition ships were required to use fuels with 0.1 % sulfur in EU harbours. The calculations have been made with emissions representative of 2009 and 2011, i.e. before and after the implementation of the stricter controls on sulfur emissions from 2010. The calculations with present emissions show that per person, an additional 0.1–0.2 years of life lost is estimated in areas close to the major ship tracks with current emission levels. Comparisons of model calculations with emissions before and after the implementation of stricter emission control on sulfur show a general decrease in calculated particle concentration. At the same time, however, an increase in ship activity has resulted in higher emissions of other components, and subsequently air concentrations, in particular of NOx, especially in and around several major ports.

Additional model calculations have been made with land-based and ship emissions representative of year 2030. Following a decrease in emissions from all sectors, air quality is expected to improve, and depositions to be reduced. Particles from shipping are expected to decrease as a result of emission controls in the SECAs. Further controls of NOx emissions from shipping are not decided, and calculations are presented with and without such controls.

Posted on 22 January 2015 | 12:00 am


Ozone production and transport over the Amazon Basin during the dry-to-wet and wet-to-dry transition seasons

Ozone production and transport over the Amazon Basin during the dry-to-wet and wet-to-dry transition seasons

Atmospheric Chemistry and Physics, 15, 757-782, 2015

Author(s): M. M. Bela, K. M. Longo, S. R. Freitas, D. S. Moreira, V. Beck, S. C. Wofsy, C. Gerbig, K. Wiedemann, M. O. Andreae, and P. Artaxo

The Regional Carbon Balance in Amazonia (BARCA) campaign provided the first Amazon Basin-wide aircraft measurements of ozone (O3) during both the dry-to-wet (November and December 2008) and wet-to-dry (May 2009) transition seasons. Extremely low background values (< 20 ppb) were observed to the west and north of Manaus in both seasons and in all regions during the wet-to-dry transition. On the other hand, elevated O3 levels (40–60 ppb) were seen during the dry-to-wet transition to the east and south of Manaus, where biomass burning emissions of O3 precursors were present. Chemistry simulations with the CCATT-BRAMS and WRF-Chem models are within the error bars of the observed O3 profiles in the boundary layer (0–3 km a.s.l.) in polluted conditions. However, the models overestimate O3 in the boundary layer in clean conditions, despite lacking the predominant NO source from soil. In addition, O3 simulated by the models was either within the error bars or lower than BARCA observations in mid-levels (3–5 km a.s.l.), and lower than total tropospheric O3 retrieved from the OMI/MLS instruments, which is primarily comprised of middle troposphere O3 and thus reflects long-range transport processes. Therefore, the models do a relatively poor job of representing the free troposphere-boundary layer gradient in O3 compared with aircraft and satellite observations, which could be due to missing long-range and convective transport of O3 at mid-levels. Additional simulations with WRF-Chem showed that the model O3 production is very sensitive to both the O3 deposition velocities and the NOx emissions, which were both about one-half of observed values. These results indicate the necessity of more realistic model representations of emissions, deposition, and convective processes for accurate monitoring and prediction of increases in O3 production in the Amazon Basin as the regional population grows.

Posted on 21 January 2015 | 12:00 am


Comment on "Reduced efficacy of marine cloud brightening geoengineering due to in-plume aerosol coagulation: parameterization and global implications" by Stuart et al. (2013)

Comment on "Reduced efficacy of marine cloud brightening geoengineering due to in-plume aerosol coagulation: parameterization and global implications" by Stuart et al. (2013)

Atmospheric Chemistry and Physics, 15, 753-756, 2015

Author(s): S. Anand and Y. S. Mayya

We examine the parameterized model of Stuart et al. (2013) vis-à-vis a diffusion-based model proposed by us earlier (Anand and Mayya, 2011) to estimate the fraction of aerosol particles surviving coagulation in a dispersing plume. While the Stuart et al. approach is based on the solutions to the coagulation problem in an expanding plume model, the diffusion-based approach solves the diffusion–coagulation equation for a steady-state standing plume to arrive at the survival fraction correlations. We discuss the differences in the functional forms of the survival fraction expressions obtained in the two approaches and compare the results for the case studies presented in Stuart et al. (2013) involving different particle emission rates and atmospheric stability categories. There appears to be a better agreement between the two models at higher survival fractions as compared to lower survival fractions; on the whole, the two models agree with each other within a difference of 10%. The diffusion-based expression involves a single exponent fit to a theoretically generated similarity variable combining the parameters of the problem with inbuilt exponents and hence avoids the multi-exponent parameterization exercise. It also possesses a wider range of applicability in respect of the source and atmospheric parameters as compared to that based on parameterization. However, in the diffusion model, the choice of a representative value for the coagulation coefficient is more prescriptive than rigorous, which has been addressed in a more satisfactory manner by the parameterization method. The present comparative exercise, although limited in scope, confirms the importance of aerosol microphysical processes envisaged by Stuart et al. for cloud brightening applications. In a larger context, it seems to suggest that either of the two forms of expressions might be suitable for incorporation into global-/regional-scale air pollution models for predicting the contribution of localized sources to the particle number loading in the atmosphere.

Posted on 21 January 2015 | 12:00 am


Investigating types and sources of organic aerosol in Rocky Mountain National Park using aerosol mass spectrometry

Investigating types and sources of organic aerosol in Rocky Mountain National Park using aerosol mass spectrometry

Atmospheric Chemistry and Physics, 15, 737-752, 2015

Author(s): M. I. Schurman, T. Lee, Y. Sun, B. A. Schichtel, S. M. Kreidenweis, and J. L. Collett Jr.

The environmental impacts of atmospheric particles are highlighted in remote areas where visibility and ecosystem health can be degraded by even relatively low particle concentrations. Submicron particle size, composition, and source apportionment were explored at Rocky Mountain National Park using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer. This summer campaign found low average, but variable, particulate mass (PM) concentrations (max = 93.1 ?g m?3, avg. = 5.13 ± 2.72 ?g m?3) of which 75.2 ± 11.1% is organic. Low-volatility oxidized organic aerosol (LV-OOA, 39.3% of PM1 on average) identified using Positive Matrix Factorization appears to be mixed with ammonium sulfate (3.9% and 16.6% of mass, respectively), while semi-volatile OOA (27.6%) is correlated with ammonium nitrate (nitrate: 4.3%); concentrations of these mixtures are enhanced with upslope (SE) surface winds from the densely populated Front Range area, indicating the importance of transport. A local biomass burning organic aerosol (BBOA, 8.4%) source is suggested by mass spectral cellulose combustion markers (m/z 60 and 73) limited to brief, high-concentration, polydisperse events (suggesting fresh combustion), a diurnal maximum at 22:00 local standard time when campfires were set at adjacent summer camps, and association with surface winds consistent with local campfire locations. The particle characteristics determined here represent typical summertime conditions at the Rocky Mountain site based on comparison to ~10 years of meteorological, particle composition, and fire data.

Posted on 20 January 2015 | 12:00 am


Mercury vapor air–surface exchange measured by collocated micrometeorological and enclosure methods – Part I: Data comparability and method characteristics

Mercury vapor air–surface exchange measured by collocated micrometeorological and enclosure methods – Part I: Data comparability and method characteristics

Atmospheric Chemistry and Physics, 15, 685-702, 2015

Author(s): W. Zhu, J. Sommar, C.-J. Lin, and X. Feng

Reliable quantification of air–biosphere exchange flux of elemental mercury vapor (Hg0) is crucial for understanding the global biogeochemical cycle of mercury. However, there has not been a standard analytical protocol for flux quantification, and little attention has been devoted to characterize the temporal variability and comparability of fluxes measured by different methods. In this study, we deployed a collocated set of micrometeorological (MM) and dynamic flux chamber (DFC) measurement systems to quantify Hg0 flux over bare soil and low standing crop in an agricultural field. The techniques include relaxed eddy accumulation (REA), modified Bowen ratio (MBR), aerodynamic gradient (AGM) as well as dynamic flux chambers of traditional (TDFC) and novel (NDFC) designs. The five systems and their measured fluxes were cross-examined with respect to magnitude, temporal trend and correlation with environmental variables.

Fluxes measured by the MM and DFC methods showed distinct temporal trends. The former exhibited a highly dynamic temporal variability while the latter had much more gradual temporal features. The diurnal characteristics reflected the difference in the fundamental processes driving the measurements. The correlations between NDFC and TDFC fluxes and between MBR and AGM fluxes were significant (R>0.8, p<0.05), but the correlation between DFC and MM fluxes were from weak to moderate (R=0.1–0.5). Statistical analysis indicated that the median of turbulent fluxes estimated by the three independent MM techniques were not significantly different. Cumulative flux measured by TDFC is considerably lower (42% of AGM and 31% of MBR fluxes) while those measured by NDFC, AGM and MBR were similar (<10% difference). This suggests that incorporating an atmospheric turbulence property such as friction velocity for correcting the DFC-measured flux effectively bridged the gap between the Hg0 fluxes measured by enclosure and MM techniques. Cumulated flux measured by REA was ~60% higher than the gradient-based fluxes. Environmental factors have different degrees of impacts on the fluxes observed by different techniques, possibly caused by the underlying assumptions specific to each individual method. Recommendations regarding the application of flux quantification methods were made based on the data obtained in this study.

Posted on 19 January 2015 | 12:00 am


Explicit representation of subgrid variability in cloud microphysics yields weaker aerosol indirect effect in the ECHAM5-HAM2 climate model

Explicit representation of subgrid variability in cloud microphysics yields weaker aerosol indirect effect in the ECHAM5-HAM2 climate model

Atmospheric Chemistry and Physics, 15, 703-714, 2015

Author(s): J. Tonttila, H. Järvinen, and P. Räisänen

The impacts of representing cloud microphysical processes in a stochastic subcolumn framework are investigated, with emphasis on estimating the aerosol indirect effect. It is shown that subgrid treatment of cloud activation and autoconversion of cloud water to rain reduce the impact of anthropogenic aerosols on cloud properties and thus reduce the global mean aerosol indirect effect by 19%, from ?1.59 to ?1.28 W m?2. This difference is partly related to differences in the model basic state; in particular, the liquid water path (LWP) is smaller and the shortwave cloud radiative forcing weaker when autoconversion is computed separately for each subcolumn. However, when the model is retuned so that the differences in the basic state LWP and radiation balance are largely eliminated, the global-mean aerosol indirect effect is still 14% smaller (i.e. ?1.37 W m?2) than for the model version without subgrid treatment of cloud activation and autoconversion. The results show the importance of considering subgrid variability in the treatment of autoconversion. Representation of several processes in a self-consistent subgrid framework is emphasized. This paper provides evidence that omitting subgrid variability in cloud microphysics contributes to the apparently chronic overestimation of the aerosol indirect effect by climate models, as compared to satellite-based estimates.

Posted on 19 January 2015 | 12:00 am


Top-down estimates of European CH4 and N2O emissions based on four different inverse models

Top-down estimates of European CH4 and N2O emissions based on four different inverse models

Atmospheric Chemistry and Physics, 15, 715-736, 2015

Author(s): P. Bergamaschi, M. Corazza, U. Karstens, M. Athanassiadou, R. L. Thompson, I. Pison, A. J. Manning, P. Bousquet, A. Segers, A. T. Vermeulen, G. Janssens-Maenhout, M. Schmidt, M. Ramonet, F. Meinhardt, T. Aalto, L. Haszpra, J. Moncrieff, M. E. Popa, D. Lowry, M. Steinbacher, A. Jordan, S. O'Doherty, S. Piacentino, and E. Dlugokencky

European CH4 and N2O emissions are estimated for 2006 and 2007 using four inverse modelling systems, based on different global and regional Eulerian and Lagrangian transport models. This ensemble approach is designed to provide more realistic estimates of the overall uncertainties in the derived emissions, which is particularly important for verifying bottom-up emission inventories.

We use continuous observations from 10 European stations (including 5 tall towers) for CH4 and 9 continuous stations for N2O, complemented by additional European and global discrete air sampling sites. The available observations mainly constrain CH4 and N2O emissions from north-western and eastern Europe. The inversions are strongly driven by the observations and the derived total emissions of larger countries show little dependence on the emission inventories used a priori.

Three inverse models yield 26–56% higher total CH4 emissions from north-western and eastern Europe compared to bottom-up emissions reported to the UNFCCC, while one model is close to the UNFCCC values. In contrast, the inverse modelling estimates of European N2O emissions are in general close to the UNFCCC values, with the overall range from all models being much smaller than the UNFCCC uncertainty range for most countries. Our analysis suggests that the reported uncertainties for CH4 emissions might be underestimated, while those for N2O emissions are likely overestimated.

Posted on 19 January 2015 | 12:00 am


The global impact of the transport sectors on atmospheric aerosol in 2030 – Part 1: Land transport and shipping

The global impact of the transport sectors on atmospheric aerosol in 2030 – Part 1: Land transport and shipping

Atmospheric Chemistry and Physics, 15, 633-651, 2015

Author(s): M. Righi, J. Hendricks, and R. Sausen

Using the EMAC (ECHAM/MESSy Atmospheric Chemistry) global climate-chemistry model coupled to the aerosol module MADE (Modal Aerosol Dynamics model for Europe, adapted for global applications), we simulate the impact of land transport and shipping emissions on global atmospheric aerosol and climate in 2030. Future emissions of short-lived gas and aerosol species follow the four Representative Concentration Pathways (RCPs) designed in support of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We compare the resulting 2030 land-transport- and shipping-induced aerosol concentrations to the ones obtained for the year 2000 in a previous study with the same model configuration. The simulations suggest that black carbon and aerosol nitrate are the most relevant pollutants from land transport in 2000 and 2030 and their impacts are characterized by very strong regional variations during this time period. Europe and North America experience a decrease in the land-transport-induced particle pollution, although in these regions this sector remains a major source of surface-level pollution in 2030 under all RCPs. In Southeast Asia, however, a significant increase is simulated, but in this region the surface-level pollution is still controlled by other sources than land transport. Shipping-induced air pollution is mostly due to aerosol sulfate and nitrate, which show opposite trends towards 2030. Sulfate is strongly reduced as a consequence of sulfur reduction policies in ship fuels in force since 2010, while nitrate tends to increase due to the excess of ammonia following the reduction in ammonium sulfate. The aerosol-induced climate impact of both sectors is dominated by aerosol-cloud effects and is projected to decrease between 2000 and 2030, nevertheless still contributing a significant radiative forcing to Earth's radiation budget.

Posted on 19 January 2015 | 12:00 am


Observation and analysis of speciated atmospheric mercury in Shangri-La, Tibetan Plateau, China

Observation and analysis of speciated atmospheric mercury in Shangri-La, Tibetan Plateau, China

Atmospheric Chemistry and Physics, 15, 653-665, 2015

Author(s): H. Zhang, X. W. Fu, C.-J. Lin, X. Wang, and X. B. Feng

This study reports the concentrations and potential sources of speciated atmospheric mercury at the Shangri-La Atmosphere Watch Regional Station (SAWRS), a pristine high-altitude site (3580 m a.s.l.) in Tibetan Plateau, China. Total gaseous mercury (TGM, defined as the sum of gaseous elemental mercury, GEM, and gaseous oxidized mercury, GOM), GOM and particulate-bound mercury (PBM) were monitored from November 2009 to November 2010 to investigate the characteristics and potential influence of the Indian summer monsoon (ISM) and the Westerlies on atmospheric transport of mercury. The mean concentrations (± standard deviation) of TGM, PBM and GOM were 2.55 ± 0.73 ng m?3, 38.82 ± 31.26 pg m?3 and 8.22 ± 7.90 pg m?3, respectively. A notable seasonal pattern of TGM concentrations was observed with higher concentrations at the beginning and the end of the ISM season. High TGM concentrations (> 2.5 ng m−3) were associated with the transport of dry air that carried regional anthropogenic emissions from both Chinese domestic and foreign (e.g., Myanmar, Bay of Bengal, and northern India) sources based on analysis of HYSPLIT4 back trajectories. Somewhat lower PBM and GOM levels during the ISM period were attributed to the enhanced wet scavenging. The high GOM and PBM were likely caused by local photo-chemical transformation under low RH and the domestic biofuel burning in cold seasons.

Posted on 19 January 2015 | 12:00 am


Validation of OMI total ozone retrievals from the SAO ozone profile algorithm and three operational algorithms with Brewer measurements

Validation of OMI total ozone retrievals from the SAO ozone profile algorithm and three operational algorithms with Brewer measurements

Atmospheric Chemistry and Physics, 15, 667-683, 2015

Author(s): J. Bak, X. Liu, J. H. Kim, K. Chance, and D. P. Haffner

The accuracy of total ozone computed from the Smithsonian Astrophysical Observatory (SAO) optimal estimation (OE) ozone profile algorithm (SOE) applied to the Ozone Monitoring Instrument (OMI) is assessed through comparisons with ground-based Brewer spectrometer measurements from 2005 to 2008. We also compare the three OMI operational ozone products, derived from the NASA Total Ozone Mapping Spectrometer (TOMS) algorithm, the KNMI (Royal Netherlands Meteorological Institute) differential optical absorption spectroscopy (DOAS) algorithm, and KNMI's Optimal Estimation (KOE) algorithm. The best agreement is observed between SAO and Brewer, with a mean difference of within 1% at most individual stations. The KNMI OE algorithm systematically overestimates Brewer total ozone by 2% at low and mid-latitudes and 5% at high latitudes while the TOMS and DOAS algorithms underestimate it by ~1.65% on average. Standard deviations of ~1.8% are calculated for both SOE and TOMS, but DOAS and KOE have higher values of 2.2% and 2.6%, respectively. The stability of the SOE algorithm is found to have insignificant dependence on viewing geometry, cloud parameters, or total ozone column. In comparison, the KOE–Brewer differences are significantly correlated with solar and viewing zenith angles and show significant deviations depending on cloud parameters and total ozone amount. The TOMS algorithm exhibits similar stability to SOE with respect to viewing geometry and total column ozone, but has stronger cloud parameter dependence. The dependence of DOAS on observational geometry and geophysical conditions is marginal compared to KOE, but is distinct compared to the SOE and TOMS algorithms. Comparisons of all four OMI products with Brewer show no apparent long-term drift, but seasonal features are evident, especially for KOE and TOMS. The substantial differences in the KOE vs. SOE algorithm performance cannot be sufficiently explained by the use of soft calibration (in SOE) and the use of different a priori error covariance matrices; however, other algorithm details cause fitting residuals larger by a factor of 2–3 for KOE.

Posted on 19 January 2015 | 12:00 am


Arctic low-level boundary layer clouds: in situ measurements and simulations of mono- and bimodal supercooled droplet size distributions at the top layer of liquid phase clouds

Arctic low-level boundary layer clouds: in situ measurements and simulations of mono- and bimodal supercooled droplet size distributions at the top layer of liquid phase clouds

Atmospheric Chemistry and Physics, 15, 617-631, 2015

Author(s): M. Klingebiel, A. de Lozar, S. Molleker, R. Weigel, A. Roth, L. Schmidt, J. Meyer, A. Ehrlich, R. Neuber, M. Wendisch, and S. Borrmann

Aircraft borne optical in situ size distribution measurements were performed within Arctic boundary layer clouds with a special emphasis on the cloud top layer during the VERtical Distribution of Ice in Arctic clouds (VERDI) campaign in April and May 2012. An instrumented Basler BT-67 research aircraft operated out of Inuvik over the Mackenzie River delta and the Beaufort Sea in the Northwest Territories of Canada. Besides the cloud particle and hydrometeor size spectrometers the aircraft was equipped with instrumentation for aerosol, radiation and other parameters. Inside the cloud, droplet size distributions with monomodal shapes were observed for predominantly liquid-phase Arctic stratocumulus. With increasing altitude inside the cloud the droplet mean diameters grew from 10 to 20 ?m. In the upper transition zone (i.e., adjacent to the cloud-free air aloft) changes from monomodal to bimodal droplet size distributions (Mode 1 with 20 ?m and Mode 2 with 10 ?m diameter) were observed. It is shown that droplets of both modes co-exist in the same (small) air volume and the bimodal shape of the measured size distributions cannot be explained as an observational artifact caused by accumulating data point populations from different air volumes. The formation of the second size mode can be explained by (a) entrainment and activation/condensation of fresh aerosol particles, or (b) by differential evaporation processes occurring with cloud droplets engulfed in different eddies. Activation of entrained particles seemed a viable possibility as a layer of dry Arctic enhanced background aerosol (which was detected directly above the stratus cloud) might form a second mode of small cloud droplets. However, theoretical considerations and model calculations (adopting direct numerical simulation, DNS) revealed that, instead, turbulent mixing and evaporation of larger droplets are the most likely reasons for the formation of the second droplet size mode in the uppermost region of the clouds.

Posted on 16 January 2015 | 12:00 am


Multiday production of condensing organic aerosol mass in urban and forest outflow

Multiday production of condensing organic aerosol mass in urban and forest outflow

Atmospheric Chemistry and Physics, 15, 595-615, 2015

Author(s): J. Lee-Taylor, A. Hodzic, S. Madronich, B. Aumont, M. Camredon, and R. Valorso

Secondary organic aerosol (SOA) production in air masses containing either anthropogenic or biogenic (terpene-dominated) emissions is investigated using the explicit gas-phase chemical mechanism generator GECKO-A. Simulations show several-fold increases in SOA mass continuing for multiple days in the urban outflow, even as the initial air parcel is diluted into the regional atmosphere. The SOA mass increase in the forest outflow is more modest (~50%) and of shorter duration (1–2 days). The multiday production in the urban outflow stems from continuing oxidation of gas-phase precursors which persist in equilibrium with the particle phase, and can be attributed to multigenerational reaction products of both aromatics and alkanes, especially those with relatively low carbon numbers (C4–15). In particular we find large contributions from substituted maleic anhydrides and multi-substituted peroxide-bicyclic alkenes. The results show that the predicted production is a robust feature of our model even under changing atmospheric conditions and different vapor pressure schemes, and contradict the notion that SOA undergoes little mass production beyond a short initial formation period. The results imply that anthropogenic aerosol precursors could influence the chemical and radiative characteristics of the atmosphere over an extremely wide region, and that SOA measurements near precursor sources may routinely underestimate this influence.

Posted on 16 January 2015 | 12:00 am


Iodine oxide in the global marine boundary layer

Iodine oxide in the global marine boundary layer

Atmospheric Chemistry and Physics, 15, 583-593, 2015

Author(s): C. Prados-Roman, C. A. Cuevas, T. Hay, R. P. Fernandez, A. S. Mahajan, S.-J. Royer, M. Galí, R. Simó, J. Dachs, K. Großmann, D. E. Kinnison, J.-F. Lamarque, and A. Saiz-Lopez

Emitted mainly by the oceans, iodine is a halogen compound important for atmospheric chemistry due to its high ozone depletion potential and effect on the oxidizing capacity of the atmosphere. Here we present a comprehensive data set of iodine oxide (IO) measurements in the open marine boundary layer (MBL) made during the Malaspina 2010 circumnavigation. Results show IO mixing ratios ranging from 0.4 to 1 pmol mol?1 (30% uncertainty) and, complemented with additional field campaigns, this data set confirms through observations the ubiquitous presence of reactive iodine chemistry in the global marine environment. We use a global model with organic (CH3I, CH2ICl, CH2I2 and CH2IBr) and inorganic (HOI and I2) iodine ocean emissions to investigate the contribution of the different iodine source gases to the budget of IO in the global MBL. In agreement with previous estimates, our results indicate that, globally averaged, the abiotic precursors contribute about 75 % to the IO budget. However, this work reveals a strong geographical pattern in the contribution of organic vs. inorganic precursors to reactive iodine in the global MBL.

Posted on 16 January 2015 | 12:00 am


Seasonal and interannual variations in HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS

Seasonal and interannual variations in HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS

Atmospheric Chemistry and Physics, 15, 563-582, 2015

Author(s): N. Glatthor, M. Höpfner, G. P. Stiller, T. von Clarmann, B. Funke, S. Lossow, E. Eckert, U. Grabowski, S. Kellmann, A. Linden, K. A. Walker, and A. Wiegele

We present a HCN climatology of the years 2002–2012, derived from FTIR limb emission spectra measured with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the ENVISAT satellite, with the main focus on biomass burning signatures in the upper troposphere and lower stratosphere. HCN is an almost unambiguous tracer of biomass burning with a tropospheric lifetime of 5–6 months and a stratospheric lifetime of about 2 years. The MIPAS climatology is in good agreement with the HCN distribution obtained by the spaceborne ACE-FTS experiment and with airborne in situ measurements performed during the INTEX-B campaign. The HCN amounts observed by MIPAS in the southern tropical and subtropical upper troposphere have an annual cycle peaking in October–November, i.e. 1–2 months after the maximum of southern hemispheric fire emissions. The probable reason for the time shift is the delayed onset of deep convection towards austral summer. Because of overlap of varying biomass burning emissions from South America and southern Africa with sporadically strong contributions from Indonesia, the size and strength of the southern hemispheric plume have considerable interannual variations, with monthly mean maxima at, for example, 14 km between 400 and more than 700 pptv. Within 1–2 months after appearance of the plume, a considerable portion of the enhanced HCN is transported southward to as far as Antarctic latitudes. The fundamental period of HCN variability in the northern upper troposphere is also an annual cycle with varying amplitude, which in the tropics peaks in May after and during the biomass burning seasons in northern tropical Africa and southern Asia, and in the subtropics peaks in July due to trapping of pollutants in the Asian monsoon anticyclone (AMA). However, caused by extensive biomass burning in Indonesia and by northward transport of part of the southern hemispheric plume, northern HCN maxima also occur around October/November in several years, which leads to semi-annual cycles. There is also a temporal shift between enhanced HCN in northern low and mid- to high latitudes, indicating northward transport of pollutants. Due to additional biomass burning at mid- and high latitudes, this meridional transport pattern is not as clear as in the Southern Hemisphere. Upper tropospheric HCN volume mixing ratios (VMRs) above the tropical oceans decrease to below 200 pptv, presumably caused by ocean uptake, especially during boreal winter and spring. The tropical stratospheric tape recorder signal with an apparently biennial period, which was detected in MLS and ACE-FTS data from mid-2004 to mid-2007, is corroborated by MIPAS HCN data. The tape recorder signal in the whole MIPAS data set exhibits periodicities of 2 and 4 years, which are generated by interannual variations in biomass burning. The positive anomalies of the years 2003, 2007 and 2011 are caused by succession of strongly enhanced HCN from southern hemispheric and Indonesian biomass burning in boreal autumn and of elevated HCN from northern tropical Africa and the AMA in subsequent spring and summer. The anomaly of 2005 seems to be due to springtime emissions from tropical Africa followed by release from the summertime AMA. The vertical transport time of the anomalies is 1 month or less between 14 and 17 km in the upper troposphere and 8–11 months between 17 and 25 km in the lower stratosphere.

Posted on 16 January 2015 | 12:00 am


On the use of a satellite remote-sensing-based approach for determining aerosol direct radiative effect over land: a case study over China

On the use of a satellite remote-sensing-based approach for determining aerosol direct radiative effect over land: a case study over China

Atmospheric Chemistry and Physics, 15, 505-518, 2015

Author(s): A.-M. Sundström, A. Arola, P. Kolmonen, Y. Xue, G. de Leeuw, and M. Kulmala

A satellite-based approach to derive the aerosol direct shortwave (SW) radiative effect (ADRE) was studied in an environment with highly variable aerosol conditions over eastern China from March to October 2009. The method is based on using coincident SW top-of-the-atmosphere (TOA) fluxes from the Clouds and the Earth's Radiant Energy System (CERES) and aerosol optical depths (AODs) from the MODerate Resolution Imaging Spectroradiometer (MODIS) to derive SW clear-sky ADRE. The estimate for the aerosol-free TOA flux (F0,TOA) is obtained by establishing linear regression between CERES SW TOA fluxes and MODIS AODs. A normalization procedure to a fixed solar zenith angle, Earth–Sun distance and atmospheric water vapor content was applied to the CERES fluxes prior to the linear fit against AOD to reduce the flux variation not related to aerosols. In the majority of the cases, the normalization increased positive correlation between observed SW TOA fluxes and AODs, and it decreased RMSE. The key question in the satellite-based approach is the accuracy of the estimated F0,TOA. Comparison with simulated F0,TOA showed that both the satellite method and the model produced qualitatively similar spatial patterns, but absolute values differed. In 58 % of the cases the satellite-based F0,TOA was within ±10 W m−2 of the modeled value (about 7–8 % difference in flux values). Over bright surfaces, the satellite-based method tend to produce lower F0,TOA than the model. The satellite-based clear-sky estimates for median instantaneous and diurnally averaged ADRE over the study area were ?8.8 W m−2 and ?5.1 W m−2, respectively. Over heavily industrialized areas, the cooling at TOA was 2 to more than 3 times the median value, and associated with high AODs (> 0.5). Especially during the summer months, positive ADREs were observed locally over dark surfaces. This was most probably a method artifact related to systematic change of aerosol type, sub-visual cloud contamination or both.

Posted on 15 January 2015 | 12:00 am


Modeling dust as component minerals in the Community Atmosphere Model: development of framework and impact on radiative forcing

Modeling dust as component minerals in the Community Atmosphere Model: development of framework and impact on radiative forcing

Atmospheric Chemistry and Physics, 15, 537-561, 2015

Author(s): R. A. Scanza, N. Mahowald, S. Ghan, C. S. Zender, J. F. Kok, X. Liu, Y. Zhang, and S. Albani

The mineralogy of desert dust is important due to its effect on radiation, clouds and biogeochemical cycling of trace nutrients. This study presents the simulation of dust radiative forcing as a function of both mineral composition and size at the global scale, using mineral soil maps for estimating emissions. Externally mixed mineral aerosols in the bulk aerosol module in the Community Atmosphere Model version 4 (CAM4) and internally mixed mineral aerosols in the modal aerosol module in the Community Atmosphere Model version 5.1 (CAM5) embedded in the Community Earth System Model version 1.0.5 (CESM) are speciated into common mineral components in place of total dust. The simulations with mineralogy are compared to available observations of mineral atmospheric distribution and deposition along with observations of clear-sky radiative forcing efficiency. Based on these simulations, we estimate the all-sky direct radiative forcing at the top of the atmosphere as + 0.05 Wm?2 for both CAM4 and CAM5 simulations with mineralogy. We compare this to the radiative forcing from simulations of dust in release versions of CAM4 and CAM5 (+0.08 and +0.17 Wm?2) and of dust with optimized optical properties, wet scavenging and particle size distribution in CAM4 and CAM5, ?0.05 and ?0.17 Wm?2, respectively. The ability to correctly include the mineralogy of dust in climate models is hindered by its spatial and temporal variability as well as insufficient global in situ observations, incomplete and uncertain source mineralogies and the uncertainties associated with data retrieved from remote sensing methods.

Posted on 15 January 2015 | 12:00 am


A global survey of cloud overlap based on CALIPSO and CloudSat measurements

A global survey of cloud overlap based on CALIPSO and CloudSat measurements

Atmospheric Chemistry and Physics, 15, 519-536, 2015

Author(s): J. Li, J. Huang, K. Stamnes, T. Wang, Q. Lv, and H. Jin

Using 2B-CLDCLASS-LIDAR (radar–lidar) cloud classification and 2B-FLXHR-LIDAR radiation products from CloudSat over 4 years, this study evaluates the co-occurrence frequencies of different cloud types, analyzes their along-track horizontal scales and cloud radiative effects (CREs), and utilizes the vertical distributions of cloud types to evaluate cloud-overlap assumptions.

The statistical results show that high clouds, altostratus (As), altocumulus (Ac) and cumulus (Cu) tend to coexist with other cloud types. However, stratus (St) (or stratocumulus, Sc), nimbostratus (Ns) and convective clouds are much more likely to exhibit individual features than other cloud types. On average, altostratus-over-stratus/stratocumulus cloud systems have a maximum horizontal scale of 17.4 km, with a standard deviation of 23.5 km. Altocumulus-over-cumulus cloud types have a minimum scale of 2.8 km, with a standard deviation of 3.1 km. By considering the weight of each multilayered cloud type, we find that the global mean instantaneous net CREs of multilayered cloud systems during the daytime are approximately ?41.3 and ?50.2 W m?2, which account for 40.1 and 42.3% of the global mean total net CREs at the top of the atmosphere (TOA) and at the surface, respectively. The radiative contributions of high-over-altocumulus and high-over-stratus/stratocumulus (or cumulus) in the all multilayered cloud systems are dominant due to their frequency.

Considering the overlap of cloud types, the cloud fraction based on the random overlap assumption is underestimated over vast oceans, except in the west-central Pacific Ocean warm pool. Obvious overestimations mainly occur over tropical and subtropical land masses. In view of a lower degree of overlap than that predicted by the random overlap assumption to occur over the vast ocean, particularly poleward of 40° S, the study therefore suggests that a linear combination of minimum and random overlap assumptions may further improve the predictions of actual cloud fractions for multilayered cloud types (e.g., As + St/Sc and Ac + St/Sc) over the Southern Ocean. The establishment of a statistical relationship between multilayered cloud types and the environmental conditions (e.g., atmospheric vertical motion, convective stability and wind shear) would be useful for parameterization design of cloud overlap in numerical models.

Posted on 15 January 2015 | 12:00 am


Variability of BVOC emissions from a Mediterranean mixed forest in southern France with a focus on Quercus pubescens

Variability of BVOC emissions from a Mediterranean mixed forest in southern France with a focus on Quercus pubescens

Atmospheric Chemistry and Physics, 15, 431-446, 2015

Author(s): A.-C. Genard-Zielinski, C. Boissard, C. Fernandez, C. Kalogridis, J. Lathière, V. Gros, N. Bonnaire, and E. Ormeño

We aimed at quantifying biogenic volatile organic compound (BVOC) emissions in June from three Mediterranean species located at the O3HP site (southern France): Quercus pubescens, Acer monspessulanum and C. coggygria (for isoprene only). As Q. pubescens was shown to be the main BVOC emitter with isoprene representing ≈ 99% of the carbon emitted as BVOC, we mainly focused on this species. C. coggygria was found to be a non-isoprene emitter (no other BVOCs were investigated).

To fully understand both the canopy effect on Q. pubescens isoprene emissions and the inter-individual variability (tree to tree and within canopy), diurnal variations of isoprene were investigated from nine branches (seven branches located to the top of canopy at ≈ 4 m above ground level (a.g.l.), and two inside the canopy at ≈ 2 m a.g.l.).

The Q. pubescens daily mean isoprene emission rate (ERd) fluctuated between 23 and 98 ?gC gDM−1 h?1. Q. pubescens daily mean net assimilation (Pn) ranged between 5.4 and 13.8, and 2.8 and 6.4 ?mol CO2 m?2 s?1 for sunlit and shaded branches respectively. Both ERd and isoprene emission factors (Is), assessed according to Guenther et al. (1993) algorithm, varied by a factor of 4.3 among the sunlit branches. While sunlit branches ERd was clearly higher than for shaded branches, there was a non-significant variability of Is (59 to 77 ?gC gDM−1 h?1). Diurnal variations of isoprene emission rates (ERs) for sunlit branches were also investigated. ERs were detected at dawn 2 h after Pn became positive and were mostly exponentially dependent on Pn. Diurnal variations of ERs were not equally well described throughout the day by temperature (CT) and light (CL) parameters according to G93 algorithm. Temperature had more impact than photosynthetically active radiation (PAR) on the morning emissions increase, and ER was no longer correlated to CL × CT between solar noon (maximum ER) and mid-afternoon, possibly due to thermal stress of the plant. A comparison between measured and calculated emissions using two isoprene algorithms (G93 and MEGAN – Model of Emissions of Gases and Aerosols from Nature) highlighted the importance of isoprene emission factor Is value used, and some weakness in assessing isoprene emissions under Mediterranean climate conditions (drought) with current isoprene models.

Posted on 14 January 2015 | 12:00 am


Improved AIOMFAC model parameterisation of the temperature dependence of activity coefficients for aqueous organic mixtures

Improved AIOMFAC model parameterisation of the temperature dependence of activity coefficients for aqueous organic mixtures

Atmospheric Chemistry and Physics, 15, 447-493, 2015

Author(s): G. Ganbavale, A. Zuend, C. Marcolli, and T. Peter

This study presents a new, improved parameterisation of the temperature dependence of activity coefficients in the AIOMFAC (Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients) model applicable for aqueous as well as water-free organic solutions. For electrolyte-free organic and organic–water mixtures the AIOMFAC model uses a group-contribution approach based on UNIFAC (UNIversal quasi-chemical Functional-group Activity Coefficients). This group-contribution approach explicitly accounts for interactions among organic functional groups and between organic functional groups and water. The previous AIOMFAC version uses a simple parameterisation of the temperature dependence of activity coefficients, aimed to be applicable in the temperature range from ~ 275 to ~ 400 K. With the goal to improve the description of a wide variety of organic compounds found in atmospheric aerosols, we extend the AIOMFAC parameterisation for the functional groups carboxyl, hydroxyl, ketone, aldehyde, ether, ester, alkyl, aromatic carbon-alcohol, and aromatic hydrocarbon to atmospherically relevant low temperatures. To this end we introduce a new parameterisation for the temperature dependence. The improved temperature dependence parameterisation is derived from classical thermodynamic theory by describing effects from changes in molar enthalpy and heat capacity of a multi-component system. Thermodynamic equilibrium data of aqueous organic and water-free organic mixtures from the literature are carefully assessed and complemented with new measurements to establish a comprehensive database, covering a wide temperature range (~ 190 to ~ 440 K) for many of the functional group combinations considered. Different experimental data types and their processing for the estimation of AIOMFAC model parameters are discussed. The new AIOMFAC parameterisation for the temperature dependence of activity coefficients from low to high temperatures shows an overall improvement of 28% in comparison to the previous model version, when both versions are compared to our database of experimentally determined activity coefficients and related thermodynamic data. When comparing the previous and new AIOMFAC model parameterisations to the subsets of experimental data with all temperatures below 274 K or all temperatures above 322 K (i.e. outside a 25 K margin of the reference temperature of 298 K), applying the new parameterisation leads to 37% improvement in each of the two temperature ranges considered. The new parameterisation of AIOMFAC agrees well with a large number of experimental data sets. Larger model–measurement discrepancies were found particularly for some of the systems containing multi-functional organic compounds. The affected systems were typically also poorly represented at room temperature and further improvements will be necessary to achieve better performance of AIOMFAC in these cases (assuming the experimental data are reliable). The performance of the AIOMFAC parameterisation is typically better for systems containing relatively small organic compounds and larger deviations may occur in mixtures where molecules of high structural complexity such as highly oxygenated compounds or molecules of high molecular mass (e.g. oligomers) prevail. Nevertheless, the new parameterisation enables the calculation of activity coefficients for a wide variety of different aqueous/water-free organic solutions down to the low temperatures present in the upper troposphere.

Posted on 14 January 2015 | 12:00 am


Understanding high wintertime ozone pollution events in an oil- and natural gas-producing region of the western US

Understanding high wintertime ozone pollution events in an oil- and natural gas-producing region of the western US

Atmospheric Chemistry and Physics, 15, 411-429, 2015

Author(s): R. Ahmadov, S. McKeen, M. Trainer, R. Banta, A. Brewer, S. Brown, P. M. Edwards, J. A. de Gouw, G. J. Frost, J. Gilman, D. Helmig, B. Johnson, A. Karion, A. Koss, A. Langford, B. Lerner, J. Olson, S. Oltmans, J. Peischl, G. Pétron, Y. Pichugina, J. M. Roberts, T. Ryerson, R. Schnell, C. Senff, C. Sweeney, C. Thompson, P. R. Veres, C. Warneke, R. Wild, E. J. Williams, B. Yuan, and R. Zamora

Recent increases in oil and natural gas (NG) production throughout the western US have come with scientific and public interest in emission rates, air quality and climate impacts related to this industry. This study uses a regional-scale air quality model (WRF-Chem) to simulate high ozone (O3) episodes during the winter of 2013 over the Uinta Basin (UB) in northeastern Utah, which is densely populated by thousands of oil and NG wells. The high-resolution meteorological simulations are able qualitatively to reproduce the wintertime cold pool conditions that occurred in 2013, allowing the model to reproduce the observed multi-day buildup of atmospheric pollutants and the accompanying rapid photochemical ozone formation in the UB.

Two different emission scenarios for the oil and NG sector were employed in this study. The first emission scenario (bottom-up) was based on the US Environmental Protection Agency (EPA) National Emission Inventory (NEI) (2011, version 1) for the oil and NG sector for the UB. The second emission scenario (top-down) was based on estimates of methane (CH4) emissions derived from in situ aircraft measurements and a regression analysis for multiple species relative to CH4 concentration measurements in the UB. Evaluation of the model results shows greater underestimates of CH4 and other volatile organic compounds (VOCs) in the simulation with the NEI-2011 inventory than in the case when the top-down emission scenario was used. Unlike VOCs, the NEI-2011 inventory significantly overestimates the emissions of nitrogen oxides (NOx), while the top-down emission scenario results in a moderate negative bias. The model simulation using the top-down emission case captures the buildup and afternoon peaks observed during high O3 episodes. In contrast, the simulation using the bottom-up inventory is not able to reproduce any of the observed high O3 concentrations in the UB. Simple emission reduction scenarios show that O3 production is VOC sensitive and NOx insensitive within the UB. The model results show a disproportionate contribution of aromatic VOCs to O3 formation relative to all other VOC emissions. The model analysis reveals that the major factors driving high wintertime O3 in the UB are shallow boundary layers with light winds, high emissions of VOCs from oil and NG operations compared to NOx emissions, enhancement of photolysis fluxes and reduction of O3 loss from deposition due to snow cover.

Posted on 14 January 2015 | 12:00 am


Exploring the chemical fate of the sulfate radical anion by reaction with sulfur dioxide in the gas phase

Exploring the chemical fate of the sulfate radical anion by reaction with sulfur dioxide in the gas phase

Atmospheric Chemistry and Physics, 15, 495-503, 2015

Author(s): N. T. Tsona, N. Bork, and H. Vehkamäki

The gas phase reaction between SO4(H2O)n and SO2, n = 0–2, is investigated using ab initio calculations and kinetic modelling. Structures of reactants, transition states and products are reported. Our calculations predict that the SO2SO4(H2O)n cluster ion, which is formed upon SO2 and SO4(H2O)n collision, can isomerize to SO3SO3(H2O)n. The overall reaction is SO2 oxidation by the SO4(H2O)n anionic cluster. The results show that SO4(H2O)n is a good SO2 oxidant, especially at low relative humidity, with a reaction rate constant up to 1.5 × 10−10 cm3 molecule−1s−1. At high relative humidity, instead, the re-evaporation of SO2 from the SO2SO4(H2O)n cluster ion is favoured.

Posted on 14 January 2015 | 12:00 am


Importance of transboundary transport of biomass burning emissions to regional air quality in Southeast Asia during a high fire event

Importance of transboundary transport of biomass burning emissions to regional air quality in Southeast Asia during a high fire event

Atmospheric Chemistry and Physics, 15, 363-373, 2015

Author(s): B. Aouizerats, G. R. van der Werf, R. Balasubramanian, and R. Betha

Smoke from biomass and peat burning has a notable impact on ambient air quality and climate in the Southeast Asia (SEA) region. We modeled a large fire-induced haze episode in 2006 stemming mostly from Indonesia using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem). We focused on the evolution of the fire plume composition and its interaction with the urbanized area of the city state of Singapore, and on comparisons of modeled and measured aerosol and carbon monoxide (CO) concentrations. Two simulations were run with WRF-Chem using the complex volatility basis set (VBS) scheme to reproduce primary and secondary aerosol evolution and concentration. The first simulation referred to as WRF-FIRE included anthropogenic, biogenic and biomass burning emissions from the Global Fire Emissions Database (GFED3) while the second simulation referred to as WRF-NOFIRE was run without emissions from biomass burning. To test model performance, we used three independent data sets for comparison including airborne measurements of particulate matter (PM) with a diameter of 10 ?m or less (PM10) in Singapore, CO measurements in Sumatra, and aerosol optical depth (AOD) column observations from four satellite-based sensors. We found reasonable agreement between the model runs and both ground-based measurements of CO and PM10. The comparison with AOD was less favorable and indicated the model underestimated AOD, although the degree of mismatch varied between different satellite data sets. During our study period, forest and peat fires in Sumatra were the main cause of enhanced aerosol concentrations from regional transport over Singapore. Analysis of the biomass burning plume showed high concentrations of primary organic aerosols (POA) with values up to 600 μg m−3 over the fire locations. The concentration of POA remained quite stable within the plume between the main burning region and Singapore while the secondary organic aerosol (SOA) concentration slightly increased. However, the absolute concentrations of SOA (up to 20 μg m−3) were much lower than those from POA, indicating a minor role of SOA in these biomass burning plumes. Our results show that about 21% of the total mass loading of ambient PM10 during the July–October study period in Singapore was due to biomass and peat burning in Sumatra, but this contribution increased during high burning periods. In total, our model results indicated that during 35 days aerosol concentrations in Singapore were above the threshold of 50 μg m−3 day−1 indicating poor air quality. During 17 days this was due to fires, based on the difference between the simulations with and without fires. Local pollution in combination with recirculation of air masses was probably the main cause of poor air quality during the other 18 days, although fires from Sumatra and probably also from Kalimantan (Indonesian part of the island of Borneo) added to the enhanced PM10 concentrations. The model versus measurement comparisons highlighted that for our study period and region the GFED3 biomass burning aerosol emissions were more in line with observations than found in other studies. This indicates that care should be taken when using AOD to constrain emissions or estimate ground-level air quality. This study also shows the need for relatively high resolution modeling to accurately reproduce the advection of air masses necessary to quantify the impacts and feedbacks on regional air quality.

Posted on 13 January 2015 | 12:00 am


Erythemal ultraviolet irradiation trends in the Iberian Peninsula from 1950 to 2011

Erythemal ultraviolet irradiation trends in the Iberian Peninsula from 1950 to 2011

Atmospheric Chemistry and Physics, 15, 375-391, 2015

Author(s): R. Román, J. Bilbao, and A. de Miguel

Erythemal ultraviolet (UVER) irradiation was reconstructed at nine Spanish locations, with series starting around 1950 in five of these places. Each series was checked by applying homogeneity tests in order to discard non-homogeneous series. Available series were used to create an averaged Iberian Peninsula UVER series. Results indicate that annual UVER irradiation in the Iberian Peninsula increased by 155 Jm?2 (6.5%) between 1950 and 2011 due to the decrease observed in atmospheric ozone rather than changes in aerosol and clouds. By contrast, annual UVER irradiation increased by 135 Jm?2 (5.6%) between 1985 and 2011, mainly due to changes in aerosol and clouds.

Posted on 13 January 2015 | 12:00 am


Development towards a global operational aerosol consensus: basic climatological characteristics of the International Cooperative for Aerosol Prediction Multi-Model Ensemble (ICAP-MME)

Development towards a global operational aerosol consensus: basic climatological characteristics of the International Cooperative for Aerosol Prediction Multi-Model Ensemble (ICAP-MME)

Atmospheric Chemistry and Physics, 15, 335-362, 2015

Author(s): W. R. Sessions, J. S. Reid, A. Benedetti, P. R. Colarco, A. da Silva, S. Lu, T. Sekiyama, T. Y. Tanaka, J. M. Baldasano, S. Basart, M. E. Brooks, T. F. Eck, M. Iredell, J. A. Hansen, O. C. Jorba, H.-M. H. Juang, P. Lynch, J.-J. Morcrette, S. Moorthi, J. Mulcahy, Y. Pradhan, M. Razinger, C. B. Sampson, J. Wang, and D. L. Westphal

Here we present the first steps in developing a global multi-model aerosol forecasting ensemble intended for eventual operational and basic research use. Drawing from members of the International Cooperative for Aerosol Prediction (ICAP) latest generation of quasi-operational aerosol models, 5-day aerosol optical thickness (AOT) forecasts are analyzed for December 2011 through November 2012 from four institutions: European Centre for Medium-Range Weather Forecasts (ECMWF), Japan Meteorological Agency (JMA), NASA Goddard Space Flight Center (GSFC), and Naval Research Lab/Fleet Numerical Meteorology and Oceanography Center (NRL/FNMOC). For dust, we also include the National Oceanic and Atmospheric Administration-National Geospatial Advisory Committee (NOAA NGAC) product in our analysis. The Barcelona Supercomputing Centre and UK Met Office dust products have also recently become members of ICAP, but have insufficient data to be included in this analysis period. A simple consensus ensemble of member and mean AOT fields for modal species (e.g., fine and coarse mode, and a separate dust ensemble) is used to create the ICAP Multi-Model Ensemble (ICAP-MME). The ICAP-MME is run daily at 00:00 UTC for 6-hourly forecasts out to 120 h. Basing metrics on comparisons to 21 regionally representative Aerosol Robotic Network (AERONET) sites, all models generally captured the basic aerosol features of the globe. However, there is an overall AOT low bias among models, particularly for high AOT events. Biomass burning regions have the most diversity in seasonal average AOT. The Southern Ocean, though low in AOT, nevertheless also has high diversity. With regard to root mean square error (RMSE), as expected the ICAP-MME placed first over all models worldwide, and was typically first or second in ranking against all models at individual sites. These results are encouraging; furthermore, as more global operational aerosol models come online, we expect their inclusion in a robust operational multi-model ensemble will provide valuable aerosol forecasting guidance.

Posted on 13 January 2015 | 12:00 am


Integrating laboratory and field data to quantify the immersion freezing ice nucleation activity of mineral dust particles

Integrating laboratory and field data to quantify the immersion freezing ice nucleation activity of mineral dust particles

Atmospheric Chemistry and Physics, 15, 393-409, 2015

Author(s): P. J. DeMott, A. J. Prenni, G. R. McMeeking, R. C. Sullivan, M. D. Petters, Y. Tobo, M. Niemand, O. Möhler, J. R. Snider, Z. Wang, and S. M. Kreidenweis

Data from both laboratory studies and atmospheric measurements are used to develop an empirical parameterization for the immersion freezing activity of natural mineral dust particles. Measurements made with the Colorado State University (CSU) continuous flow diffusion chamber (CFDC) when processing mineral dust aerosols at a nominal 105% relative humidity with respect to water (RHw) are taken as a measure of the immersion freezing nucleation activity of particles. Ice active frozen fractions vs. temperature for dusts representative of Saharan and Asian desert sources were consistent with similar measurements in atmospheric dust plumes for a limited set of comparisons available. The parameterization developed follows the form of one suggested previously for atmospheric particles of non-specific composition in quantifying ice nucleating particle concentrations as functions of temperature and the total number concentration of particles larger than 0.5 ?m diameter. Such an approach does not explicitly account for surface area and time dependencies for ice nucleation, but sufficiently encapsulates the activation properties for potential use in regional and global modeling simulations, and possible application in developing remote sensing retrievals for ice nucleating particles. A calibration factor is introduced to account for the apparent underestimate (by approximately 3, on average) of the immersion freezing fraction of mineral dust particles for CSU CFDC data processed at an RHw of 105% vs. maximum fractions active at higher RHw. Instrumental factors that affect activation behavior vs. RHw in CFDC instruments remain to be fully explored in future studies. Nevertheless, the use of this calibration factor is supported by comparison to ice activation data obtained for the same aerosols from Aerosol Interactions and Dynamics of the Atmosphere (AIDA) expansion chamber cloud parcel experiments. Further comparison of the new parameterization, including calibration correction, to predictions of the immersion freezing surface active site density parameterization for mineral dust particles, developed separately from AIDA experimental data alone, shows excellent agreement for data collected in a descent through a Saharan aerosol layer. These studies support the utility of laboratory measurements to obtain atmospherically relevant data on the ice nucleation properties of dust and other particle types, and suggest the suitability of considering all mineral dust as a single type of ice nucleating particle as a useful first-order approximation in numerical modeling investigations.

Posted on 13 January 2015 | 12:00 am


Estimation of PM10 concentrations over Seoul using multiple empirical models with AERONET and MODIS data collected during the DRAGON-Asia campaign

Estimation of PM10 concentrations over Seoul using multiple empirical models with AERONET and MODIS data collected during the DRAGON-Asia campaign

Atmospheric Chemistry and Physics, 15, 319-334, 2015

Author(s): S. Seo, J. Kim, H. Lee, U. Jeong, W. Kim, B. N. Holben, S.-W. Kim, C. H. Song, and J. H. Lim

The performance of various empirical linear models to estimate the concentrations of surface-level particulate matter with a diameter less than 10 ?m (PM10) was evaluated using Aerosol Robotic Network (AERONET) sun photometer and Moderate-Resolution Imaging Spectroradiometer (MODIS) data collected in Seoul during the Distributed Regional Aerosol Gridded Observation Network (DRAGON)-Asia campaign from March to May 2012. An observed relationship between the PM10 concentration and the aerosol optical depth (AOD) was accounted for by several parameters in the empirical models, including boundary layer height (BLH), relative humidity (RH), and effective radius of the aerosol size distribution (Reff), which was used here for the first time in empirical modeling. Among various empirical models, the model which incorporates both BLH and Reff showed the highest correlation, which indicates the strong influence of BLH and Reff on the PM10 estimations. Meanwhile, the effect of RH on the relationship between AOD and PM10 appeared to be negligible during the campaign period (spring), when RH is generally low in northeast Asia. A large spatial dependency of the empirical model performance was found by categorizing the locations of the collected data into three different site types, which varied in terms of the distances between instruments and source locations. When both AERONET and MODIS data sets were used in the PM10 estimation, the highest correlations between measured and estimated values (R = 0.76 and 0.76 using AERONET and MODIS data, respectively) were found for the residential area (RA) site type, while the poorest correlations (R = 0.61 and 0.68 using AERONET and MODIS data, respectively) were found for the near-source (NS) site type. Significant seasonal variations of empirical model performances for PM10 estimation were found using the data collected at Yonsei University (one of the DRAGON campaign sites) over a period of 17 months including the DRAGON campaign period. The best correlation between measured and estimated PM10 concentrations (R = 0.81) was found in winter, due to the presence of a stagnant air mass and low BLH conditions, which may have resulted in relatively homogeneous aerosol properties within the BLH. On the other hand, the poorest correlation between measured and estimated PM10 concentrations (R = 0.54) was found in spring, due to the influence of the long-range transport of dust to both within and above the BLH.

Posted on 13 January 2015 | 12:00 am


Simulations of atmospheric methane for Cape Grim, Tasmania, to constrain southeastern Australian methane emissions

Simulations of atmospheric methane for Cape Grim, Tasmania, to constrain southeastern Australian methane emissions

Atmospheric Chemistry and Physics, 15, 305-317, 2015

Author(s): Z. M. Loh, R. M. Law, K. D. Haynes, P. B. Krummel, L. P. Steele, P. J. Fraser, S. D. Chambers, and A. G. Williams

This study uses two climate models and six scenarios of prescribed methane emissions to compare modelled and observed atmospheric methane between 1994 and 2007, for Cape Grim, Australia (40.7° S, 144.7° E). The model simulations follow the TransCom-CH4 protocol and use the Australian Community Climate and Earth System Simulator (ACCESS) and the CSIRO Conformal-Cubic Atmospheric Model (CCAM). Radon is also simulated and used to reduce the impact of transport differences between the models and observations. Comparisons are made for air samples that have traversed the Australian continent. All six emission scenarios give modelled concentrations that are broadly consistent with those observed. There are three notable mismatches, however. Firstly, scenarios that incorporate interannually varying biomass burning emissions produce anomalously high methane concentrations at Cape Grim at times of large fire events in southeastern Australia, most likely due to the fire methane emissions being unrealistically input into the lowest model level. Secondly, scenarios with wetland methane emissions in the austral winter overestimate methane concentrations at Cape Grim during wintertime while scenarios without winter wetland emissions perform better. Finally, all scenarios fail to represent a~methane source in austral spring implied by the observations. It is possible that the timing of wetland emissions in the scenarios is incorrect with recent satellite measurements suggesting an austral spring (September–October–November), rather than winter, maximum for wetland emissions.

Posted on 13 January 2015 | 12:00 am


A global non-hydrostatic model study of a downward coupling through the tropical tropopause layer during a stratospheric sudden warming

A global non-hydrostatic model study of a downward coupling through the tropical tropopause layer during a stratospheric sudden warming

Atmospheric Chemistry and Physics, 15, 297-304, 2015

Author(s): N. Eguchi, K. Kodera, and T. Nasuno

The dynamical coupling process between the stratosphere and troposphere in the tropical tropopause layer (TTL) during a~stratospheric sudden warming (SSW) in boreal winter was investigated using simulation data from a global non-hydrostatic model (NICAM) that does not use cumulus parameterization. The model reproduced well the observed tropical tropospheric changes during the SSW, including the enhancement of convective activity following the amplification of planetary waves. Deep convective activity was enhanced in the latitude zone 20–10° S, in particular over the southwest Pacific and southwest Indian Ocean. Although the upwelling in the TTL was correlated with that in the stratosphere, the temperature tendency in the TTL changed little due to a compensation by diabatic heating originating from cloud formation. This result suggests that the stratospheric meridional circulation affects cloud formation in the TTL.

Posted on 13 January 2015 | 12:00 am


Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications

Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications

Atmospheric Chemistry and Physics, 15, 253-272, 2015

Author(s): M. R. Canagaratna, J. L. Jimenez, J. H. Kroll, Q. Chen, S. H. Kessler, P. Massoli, L. Hildebrandt Ruiz, E. Fortner, L. R. Williams, K. R. Wilson, J. D. Surratt, N. M. Donahue, J. T. Jayne, and D. R. Worsnop

Elemental compositions of organic aerosol (OA) particles provide useful constraints on OA sources, chemical evolution, and effects. The Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is widely used to measure OA elemental composition. This study evaluates AMS measurements of atomic oxygen-to-carbon (O : C), hydrogen-to-carbon (H : C), and organic mass-to-organic carbon (OM : OC) ratios, and of carbon oxidation state (OS C) for a vastly expanded laboratory data set of multifunctional oxidized OA standards. For the expanded standard data set, the method introduced by Aiken et al. (2008), which uses experimentally measured ion intensities at all ions to determine elemental ratios (referred to here as "Aiken-Explicit"), reproduces known O : C and H : C ratio values within 20% (average absolute value of relative errors) and 12%, respectively. The more commonly used method, which uses empirically estimated H2O+ and CO+ ion intensities to avoid gas phase air interferences at these ions (referred to here as "Aiken-Ambient"), reproduces O : C and H : C of multifunctional oxidized species within 28 and 14% of known values. The values from the latter method are systematically biased low, however, with larger biases observed for alcohols and simple diacids. A detailed examination of the H2O+, CO+, and CO2+ fragments in the high-resolution mass spectra of the standard compounds indicates that the Aiken-Ambient method underestimates the CO+ and especially H2O+ produced from many oxidized species. Combined AMS–vacuum ultraviolet (VUV) ionization measurements indicate that these ions are produced by dehydration and decarboxylation on the AMS vaporizer (usually operated at 600 °C). Thermal decomposition is observed to be efficient at vaporizer temperatures down to 200 °C. These results are used together to develop an "Improved-Ambient" elemental analysis method for AMS spectra measured in air. The Improved-Ambient method uses specific ion fragments as markers to correct for molecular functionality-dependent systematic biases and reproduces known O : C (H : C) ratios of individual oxidized standards within 28% (13%) of the known molecular values. The error in Improved-Ambient O : C (H : C) values is smaller for theoretical standard mixtures of the oxidized organic standards, which are more representative of the complex mix of species present in ambient OA. For ambient OA, the Improved-Ambient method produces O : C (H : C) values that are 27% (11%) larger than previously published Aiken-Ambient values; a corresponding increase of 9% is observed for OM : OC values. These results imply that ambient OA has a higher relative oxygen content than previously estimated. The OS C values calculated for ambient OA by the two methods agree well, however (average relative difference of 0.06 OS C units). This indicates that OS C is a more robust metric of oxidation than O : C, likely since OS C is not affected by hydration or dehydration, either in the atmosphere or during analysis.

Posted on 12 January 2015 | 12:00 am


Global investigation of the Mg atom and ion layers using SCIAMACHY/Envisat observations between 70 and 150 km altitude and WACCM-Mg model results

Global investigation of the Mg atom and ion layers using SCIAMACHY/Envisat observations between 70 and 150 km altitude and WACCM-Mg model results

Atmospheric Chemistry and Physics, 15, 273-295, 2015

Author(s): M. P. Langowski, C. von Savigny, J. P. Burrows, W. Feng, J. M. C. Plane, D. R. Marsh, D. Janches, M. Sinnhuber, A. C. Aikin, and P. Liebing

Mg and Mg+ concentration fields in the upper mesosphere/lower thermosphere (UMLT) region are retrieved from SCIAMACHY/Envisat limb measurements of Mg and Mg+ dayglow emissions using a 2-D tomographic retrieval approach. The time series of monthly mean Mg and Mg+ number density and vertical column density in different latitudinal regions are presented. Data from the limb mesosphere–thermosphere mode of SCIAMACHY/Envisat are used, which cover the 50 to 150 km altitude region with a vertical sampling of ?3.3 km and latitudes up to 82°. The high latitudes are not observed in the winter months, because there is no dayglow emission during polar night. The measurements were performed every 14 days from mid-2008 until April 2012. Mg profiles show a peak at around 90 km altitude with a density between 750 cm−3 and 1500 cm−3. Mg does not show strong seasonal variation at latitudes below 40°. For higher latitudes the density is lower and only in the Northern Hemisphere a seasonal cycle with a summer minimum is observed. The Mg+ peak occurs 5–15 km above the neutral Mg peak altitude. These ions have a significant seasonal cycle with a summer maximum in both hemispheres at mid and high latitudes. The strongest seasonal variations of Mg+ are observed at latitudes between 20 and 40° and the density at the peak altitude ranges from 500 cm−3 to 4000 cm−3. The peak altitude of the ions shows a latitudinal dependence with a maximum at mid latitudes that is up to 10 km higher than the peak altitude at the equator.

The SCIAMACHY measurements are compared to other measurements and WACCM model results. The WACCM results show a significant seasonal variability for Mg with a summer minimum, which is more clearly pronounced than for SCIAMACHY, and globally a higher peak density than the SCIAMACHY results. Although the peak density of both is not in agreement, the vertical column density agrees well, because SCIAMACHY and WACCM profiles have different widths. The agreement between SCIAMACHY and WACCM results is much better for Mg+ with both showing the same seasonality and similar peak density. However, there are also minor differences, e.g. WACCM showing a nearly constant altitude of the Mg+ layer's peak density for all latitudes and seasons.

Posted on 12 January 2015 | 12:00 am


The impact of dust storms on the Arabian Peninsula and the Red Sea

The impact of dust storms on the Arabian Peninsula and the Red Sea

Atmospheric Chemistry and Physics, 15, 199-222, 2015

Author(s): P. Jish Prakash, G. Stenchikov, S. Kalenderski, S. Osipov, and H. Bangalath

Located in the dust belt, the Arabian Peninsula is a major source of atmospheric dust. Frequent dust outbreaks and some 15 to 20 dust storms per year have profound effects on all aspects of human activity and natural processes in this region. To quantify the effect of severe dust events on radiation fluxes and regional climate characteristics, we simulated the storm that occurred from 18 to 20 March 2012 using a regional weather research forecast model fully coupled with the chemistry/aerosol module (WRF–Chem). This storm swept over a remarkably large area affecting the entire Middle East, northeastern Africa, Afghanistan, and Pakistan. It was caused by a southward propagating cold front, and the associated winds activated the dust production in river valleys of the lower Tigris and Euphrates in Iraq; the coastal areas in Kuwait, Iran, and the United Arab Emirates; the Rub al Khali, An Nafud, and Ad Dahna deserts; and along the Red Sea coast on the west side of the Arabian Peninsula. Our simulation results compare well with available ground-based and satellite observations. We estimate the total amount of dust generated by the storm to have reached 94 Mt. Approximately 78% of this dust was deposited within the calculation domain. The Arabian Sea and Persian Gulf received 5.3 Mt and the Red Sea 1.2 Mt of dust. Dust particles bring nutrients to marine ecosystems, which is especially important for the oligotrophic Northern Red Sea. However, their contribution to the nutrient balance in the Red Sea remains largely unknown. By scaling the effect of one storm to the number of dust storms observed annually over the Red Sea, we estimate the annual dust deposition to the Red Sea, associated with major dust storms, to be 6 Mt.

Posted on 12 January 2015 | 12:00 am


Seasonal in situ observations of glyoxal and methylglyoxal over the temperate oceans of the Southern Hemisphere

Seasonal in situ observations of glyoxal and methylglyoxal over the temperate oceans of the Southern Hemisphere

Atmospheric Chemistry and Physics, 15, 223-240, 2015

Author(s): S. J. Lawson, P. W. Selleck, I. E. Galbally, M. D. Keywood, M. J. Harvey, C. Lerot, D. Helmig, and Z. Ristovski

The dicarbonyls glyoxal and methylglyoxal have been measured with 2,4-dinitrophenylhydrazine (2,4-DNPH) cartridges and high-performance liquid chromatography (HPLC), optimised for dicarbonyl detection, in clean marine air over the temperate Southern Hemisphere (SH) oceans. Measurements of a range of dicarbonyl precursors (volatile organic compounds, VOCs) were made in parallel. These are the first in situ measurements of glyoxal and methylglyoxal over the remote temperate oceans. Six 24 h samples were collected in summer (February–March) over the Chatham Rise in the south-west Pacific Ocean during the Surface Ocean Aerosol Production (SOAP) voyage in 2012, while 34 24 h samples were collected at Cape Grim Baseline Air Pollution Station in the late winter (August–September) of 2011. Average glyoxal mixing ratios in clean marine air were 7 ppt at Cape Grim and 23 ppt over Chatham Rise. Average methylglyoxal mixing ratios in clean marine air were 28 ppt at Cape Grim and 10 ppt over Chatham Rise. The mixing ratios of glyoxal at Cape Grim are the lowest observed over the remote oceans, while mixing ratios over Chatham Rise are in good agreement with other temperate and tropical observations, including concurrent Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations. Methylglyoxal mixing ratios at both sites are comparable to the only other marine methylglyoxal observations available over the tropical Northern Hemisphere (NH) ocean. Ratios of glyoxal : methylglyoxal > 1 over Chatham Rise but < 1 at Cape Grim suggest that a different formation and/or loss processes or rates dominate at each site. Dicarbonyl precursor VOCs, including isoprene and monoterpenes, are used to calculate an upper-estimate yield of glyoxal and methylglyoxal in the remote marine boundary layer and explain at most 1–3 ppt of dicarbonyls observed, corresponding to 10% and 17% of the observed glyoxal and 29 and 10% of the methylglyoxal at Chatham Rise and Cape Grim, respectively, highlighting a significant but as yet unknown production mechanism. Surface-level glyoxal observations from both sites were converted to vertical columns and compared to average vertical column densities (VCDs) from GOME-2 satellite retrievals. Both satellite columns and in situ observations are higher in summer than winter; however, satellite vertical column densities exceeded the surface observations by more than 1.5 × 1014 molecules cm?2 at both sites. This discrepancy may be due to the incorrect assumption that all glyoxal observed by satellite is within the boundary layer, or it may be due to challenges retrieving low VCDs of glyoxal over the oceans due to interferences by liquid water absorption or the use of an inappropriate normalisation reference value in the retrieval algorithm. This study provides much-needed data to verify the presence of these short-lived gases over the remote ocean and provide further evidence of an as yet unidentified source of both glyoxal and also methylglyoxal over the remote oceans.

Posted on 12 January 2015 | 12:00 am


Mapping CH4 : CO2 ratios in Los Angeles with CLARS-FTS from Mount Wilson, California

Mapping CH4 : CO2 ratios in Los Angeles with CLARS-FTS from Mount Wilson, California

Atmospheric Chemistry and Physics, 15, 241-252, 2015

Author(s): K. W. Wong, D. Fu, T. J. Pongetti, S. Newman, E. A. Kort, R. Duren, Y.-K. Hsu, C. E. Miller, Y. L. Yung, and S. P. Sander

The Los Angeles megacity, which is home to more than 40% of the population in California, is the second largest megacity in the United States and an intense source of anthropogenic greenhouse gases (GHGs). Quantifying GHG emissions from the megacity and monitoring their spatiotemporal trends are essential to be able to understand the effectiveness of emission control policies. Here we measure carbon dioxide (CO2) and methane (CH4) across the Los Angeles megacity using a novel approach – ground-based remote sensing from a mountaintop site. A Fourier transform spectrometer (FTS) with agile pointing optics, located on Mount Wilson at 1.67 km above sea level, measures reflected near-infrared sunlight from 29 different surface targets on Mount Wilson and in the Los Angeles megacity to retrieve the slant column abundances of CO2, CH4 and other trace gases above and below Mount Wilson. This technique provides persistent space- and time-resolved observations of path-averaged dry-air GHG concentrations, XGHG, in the Los Angeles megacity and simulates observations from a geostationary satellite. In this study, we combined high-sensitivity measurements from the FTS and the panorama from Mount Wilson to characterize anthropogenic CH4 emissions in the megacity using tracer–tracer correlations. During the period between September 2011 and October 2013, the observed XCH4 : XCO2 excess ratio, assigned to anthropogenic activities, varied from 5.4 to 7.3 ppb CH4 (ppm CO2)−1, with an average of 6.4 ± 0.5 ppb CH4 (ppm CO2)−1 compared to the value of 4.6 ± 0.9 ppb CH4 (ppm CO2)−1 expected from the California Air Resources Board (CARB) bottom-up emission inventory. Persistent elevated XCH4 : XCO2 excess ratios were observed in Pasadena and in the eastern Los Angeles megacity. Using the FTS observations on Mount Wilson and the bottom-up CO2 emission inventory, we derived a top-down CH4 emission of 0.39 ± 0.06 Tg CH4 year?1 in the Los Angeles megacity. This is 18–61% larger than the state government's bottom-up CH4 emission inventory and consistent with previous studies.

Posted on 12 January 2015 | 12:00 am


Simulations of a cold-air pool associated with elevated wintertime ozone in the Uintah Basin, Utah

Simulations of a cold-air pool associated with elevated wintertime ozone in the Uintah Basin, Utah

Atmospheric Chemistry and Physics, 15, 135-151, 2015

Author(s): E. M. Neemann, E. T. Crosman, J. D. Horel, and L. Avey

Numerical simulations are used to investigate the meteorological characteristics of the 31 January–6 February 2013 cold-air pool in the Uintah Basin, Utah, and the resulting high ozone concentrations. Flow features affecting cold-air pools and air quality in the Uintah Basin are studied, including the following: penetration of clean air into the basin from across the surrounding mountains, elevated easterlies within the inversion layer, and thermally driven slope and valley flows. The sensitivity of the boundary layer structure to snow cover variations and cloud microphysics are also examined. Snow cover increases boundary layer stability by enhancing the surface albedo, reducing the absorbed solar insolation at the surface, and lowering near-surface air temperatures. Snow cover also increases ozone levels by enhancing solar radiation available for photochemical reactions. Ice-dominant clouds enhance cold-air pool strength compared to liquid-dominant clouds by increasing nocturnal cooling and decreasing longwave cloud forcing.

Posted on 9 January 2015 | 12:00 am


Global and regional modeling of clouds and aerosols in the marine boundary layer during VOCALS: the VOCA intercomparison

Global and regional modeling of clouds and aerosols in the marine boundary layer during VOCALS: the VOCA intercomparison

Atmospheric Chemistry and Physics, 15, 153-172, 2015

Author(s): M. C. Wyant, C. S. Bretherton, R. Wood, G. R. Carmichael, A. Clarke, J. Fast, R. George, W. I. Gustafson Jr., C. Hannay, A. Lauer, Y. Lin, J.-J. Morcrette, J. Mulcahy, P. E. Saide, S. N. Spak, and Q. Yang

A diverse collection of models are used to simulate the marine boundary layer in the southeast Pacific region during the period of the October–November 2008 VOCALS REx (VAMOS Ocean Cloud Atmosphere Land Study Regional Experiment) field campaign. Regional models simulate the period continuously in boundary-forced free-running mode, while global forecast models and GCMs (general circulation models) are run in forecast mode. The models are compared to extensive observations along a line at 20° S extending westward from the South American coast. Most of the models simulate cloud and aerosol characteristics and gradients across the region that are recognizably similar to observations, despite the complex interaction of processes involved in the problem, many of which are parameterized or poorly resolved. Some models simulate the regional low cloud cover well, though many models underestimate MBL (marine boundary layer) depth near the coast. Most models qualitatively simulate the observed offshore gradients of SO2, sulfate aerosol, CCN (cloud condensation nuclei) concentration in the MBL as well as differences in concentration between the MBL and the free troposphere. Most models also qualitatively capture the decrease in cloud droplet number away from the coast. However, there are large quantitative intermodel differences in both means and gradients of these quantities. Many models are able to represent episodic offshore increases in cloud droplet number and aerosol concentrations associated with periods of offshore flow. Most models underestimate CCN (at 0.1% supersaturation) in the MBL and free troposphere. The GCMs also have difficulty simulating coastal gradients in CCN and cloud droplet number concentration near the coast. The overall performance of the models demonstrates their potential utility in simulating aerosol–cloud interactions in the MBL, though quantitative estimation of aerosol–cloud interactions and aerosol indirect effects of MBL clouds with these models remains uncertain.

Posted on 9 January 2015 | 12:00 am


Inverse modelling of CH4 emissions for 2010–2011 using different satellite retrieval products from GOSAT and SCIAMACHY

Inverse modelling of CH4 emissions for 2010–2011 using different satellite retrieval products from GOSAT and SCIAMACHY

Atmospheric Chemistry and Physics, 15, 113-133, 2015

Author(s): M. Alexe, P. Bergamaschi, A. Segers, R. Detmers, A. Butz, O. Hasekamp, S. Guerlet, R. Parker, H. Boesch, C. Frankenberg, R. A. Scheepmaker, E. Dlugokencky, C. Sweeney, S. C. Wofsy, and E. A. Kort

At the beginning of 2009 new space-borne observations of dry-air column-averaged mole fractions of atmospheric methane (XCH4) became available from the Thermal And Near infrared Sensor for carbon Observations–Fourier Transform Spectrometer (TANSO-FTS) instrument on board the Greenhouse Gases Observing SATellite (GOSAT). Until April 2012 concurrent {methane (CH4) retrievals} were provided by the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) instrument on board the ENVironmental SATellite (ENVISAT). The GOSAT and SCIAMACHY XCH4 retrievals can be compared during the period of overlap. We estimate monthly average CH4 emissions between January 2010 and December 2011, using the TM5-4DVAR inverse modelling system. In addition to satellite data, high-accuracy measurements from the Cooperative Air Sampling Network of the National Oceanic and Atmospheric Administration Earth System Research Laboratory (NOAA ESRL) are used, providing strong constraints on the remote surface atmosphere. We discuss five inversion scenarios that make use of different GOSAT and SCIAMACHY XCH4 retrieval products, including two sets of GOSAT proxy retrievals processed independently by the Netherlands Institute for Space Research (SRON)/Karlsruhe Institute of Technology (KIT), and the University of Leicester (UL), and the RemoTeC "Full-Physics" (FP) XCH4 retrievals available from SRON/KIT. The GOSAT-based inversions show significant reductions in the root mean square (rms) difference between retrieved and modelled XCH4, and require much smaller bias corrections compared to the inversion using SCIAMACHY retrievals, reflecting the higher precision and relative accuracy of the GOSAT XCH4. Despite the large differences between the GOSAT and SCIAMACHY retrievals, 2-year average emission maps show overall good agreement among all satellite-based inversions, with consistent flux adjustment patterns, particularly across equatorial Africa and North America. Over North America, the satellite inversions result in a significant redistribution of CH4 emissions from North-East to South-Central United States. This result is consistent with recent independent studies suggesting a systematic underestimation of CH4 emissions from North American fossil fuel sources in bottom-up inventories, likely related to natural gas production facilities. Furthermore, all four satellite inversions yield lower CH4 fluxes across the Congo basin compared to the NOAA-only scenario, but higher emissions across tropical East Africa. The GOSAT and SCIAMACHY inversions show similar performance when validated against independent shipboard and aircraft observations, and XCH4 retrievals available from the Total Carbon Column Observing Network (TCCON).

Posted on 9 January 2015 | 12:00 am


Air quality and atmospheric deposition in the eastern US: 20 years of change

Air quality and atmospheric deposition in the eastern US: 20 years of change

Atmospheric Chemistry and Physics, 15, 173-197, 2015

Author(s): J. E. Sickles II and D. S. Shadwick

Data collected in the eastern US between 1990 and 2009 at 34 paired dry and wet monitoring sites are examined. A goal is to evaluate the air quality impacts occurring between 1990 and 2009 that are associated with concurrent legislatively mandated changes in emissions. Four 5-year periods, 1990–1994 (P1), 1995–1999 (P2), 2000–2004 (P3), and 2005–2009 (P4) are considered, with a primary focus on P1-to-P4 changes. Results suggest that legislatively mandated air pollution mitigation strategies have been successful in improving air quality and reducing atmospheric deposition in the eastern US.

Respective P1-to-P4 reductions of estimated sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions in the eastern US are 50 and 42%. Corresponding behavior of the following metrics associated with these emissions reductions is examined: monitored atmospheric concentrations of SO2, aerosol sulfate (SO4), and oxidized sulfur (S); dry, wet, and total deposition of S; monitored atmospheric concentrations of nitric acid (HNO3), aerosol nitrate (NO3), and their sum, oxidized nitrogen (OxN); dry, wet, and total deposition of OxN; monitored atmospheric concentration of aerosol ammonium (NH4); dry, wet, and total deposition of NH4; summed monitored atmospheric concentration of oxidized and reduced nitrogen (N); dry, wet, and total deposition of N; wet deposition of hydrogen ion (H+); monitored atmospheric concentration of ozone (O3); dry deposition of O3; and the summed monitored atmospheric concentration of aerosol NO3, SO4, and NH4 (Clean Air Status and Trends Network particulate matter – CASTNET PM). Other metrics (e.g., ratios of dry to total deposition) are also considered.

Selected period-to-period changes of air quality and deposition metrics at site, regional, and seasonal scales are discussed. As an example, despite P1-to-P3 reductions in estimated emissions of both SO2 and NOx, aerosol NO3 concentration increased in the east, with widespread wintertime numerical increases in both aerosol NO3 concentration and CASTNET PM. However, a reversal of this behavior is associated with continuing P3-to-P4 reductions of SO2 and NOx emissions. Thus, additional P3-to-P4 reductions of these emissions, especially NOx, appear to have made progress in altering the chemical regime of the wintertime eastern US atmosphere so that future emissions reductions and their resulting reductions in aerosol concentrations may no longer be accompanied by sub-linear changes (or actual increases) in CASTNET PM.

Posted on 9 January 2015 | 12:00 am


Constraints on Asian ozone using Aura TES, OMI and Terra MOPITT

Constraints on Asian ozone using Aura TES, OMI and Terra MOPITT

Atmospheric Chemistry and Physics, 15, 99-112, 2015

Author(s): Z. Jiang, J. R. Worden, D. B. A. Jones, J.-T. Lin, W. W. Verstraeten, and D. K. Henze

Rapid industrialization in Asia in the last two decades has resulted in a significant increase in Asian ozone (O3) precursor emissions with likely a corresponding increase in the export of O3 and its precursors. However, the relationship between this increasing O3, the chemical environment, O3 production efficiency, and the partitioning between anthropogenic and natural precursors is unclear. In this work, we use satellite measurements of O3, CO and NO2 from TES (Tropospheric Emission Spectrometer), MOPITT (Measurement of Pollution In The Troposphere) and OMI (Ozone Monitoring Instrument) to quantify O3 precursor emissions for 2006 and their impact on free tropospheric O3 over northeastern Asia, where pollution is typically exported globally due to strong westerlies. Using the GEOS-Chem (Goddard Earth Observing System Chemistry) global chemical transport model, we test the modeled seasonal and interannual variation of O3 based on prior and updated O3 precursor emissions where the updated emissions of CO and NOx are based on satellite measurements of CO and NO2. We show that the observed TES O3 variability and amount are consistent with the model for these updated emissions. However, there is little difference in the modeled ozone between the updated and prior emissions. For example, for the 2006 June time period, the prior and posterior NOx emissions were 14% different over China but the modeled ozone in the free troposphere was only 2.5% different. Using the adjoint of GEOS-Chem we partition the relative contributions of natural and anthropogenic sources to free troposphere O3 in this region. We find that the influence of lightning NOx in the summer is comparable to the contribution from surface emissions but smaller for other seasons. China is the primary contributor of anthropogenic CO, emissions and their export during the summer. While the posterior CO emissions improved the comparison between model and TES by 32%, on average, this change also had only a small effect on the free tropospheric ozone. Our results show that the influence of India and southeastern Asia emissions on O3 pollution export to the northwestern Pacific is sizeable, comparable with Chinese emissions in winter, about 50% of Chinese emissions in spring and fall, and approximately 20% of the emissions in the summer.

Posted on 8 January 2015 | 12:00 am


Tracing the second stage of ozone recovery in the Antarctic ozone-hole with a "big data" approach to multivariate regressions

Tracing the second stage of ozone recovery in the Antarctic ozone-hole with a "big data" approach to multivariate regressions

Atmospheric Chemistry and Physics, 15, 79-97, 2015

Author(s): A. T. J. de Laat, R. J. van der A, and M. van Weele

This study presents a sensitivity analysis of multivariate regressions of recent springtime Antarctic vortex ozone trends using a "big data" ensemble approach.

Our results indicate that the poleward heat flux (Eliassen–Palm flux) and the effective chlorine loading respectively explain most of the short-term and long-term variability in different Antarctic springtime total ozone records. The inclusion in the regression of stratospheric volcanic aerosols, solar variability and the quasi-biennial oscillation is shown to increase rather than decrease the overall uncertainty in the attribution of Antarctic springtime ozone because of large uncertainties in their respective records.

Calculating the trend significance for the ozone record from the late 1990s onwards solely based on the fit of the effective chlorine loading is not recommended, as this does not take fit residuals into account, resulting in too narrow uncertainty intervals, while the fixed temporal change of the effective chlorine loading does not allow for any flexibility in the trends.

When taking fit residuals into account in a piecewise linear trend fit, we find that approximately 30–60% of the regressions in the full ensemble result in a statistically significant positive springtime ozone trend over Antarctica from the late 1990s onwards. Analysis of choices and uncertainties in time series show that, depending on choices in time series and parameters, the fraction of statistically significant trends in parts of the ensemble can range from negligible to a complete 100% significance. We also find that, consistent with expectations, the number of statistically significant trends increases with increasing record length.

Although our results indicate that the use multivariate regressions is a valid approach for assessing the state of Antarctic ozone hole recovery, and it can be expected that results will move towards more confidence in recovery with increasing record length, uncertainties in choices currently do not yet support formal identification of recovery of the Antarctic ozone hole.

Posted on 8 January 2015 | 12:00 am


Aqueous-phase oligomerization of methyl vinyl ketone through photooxidation – Part 1: Aging processes of oligomers

Aqueous-phase oligomerization of methyl vinyl ketone through photooxidation – Part 1: Aging processes of oligomers

Atmospheric Chemistry and Physics, 15, 21-35, 2015

Author(s): P. Renard, F. Siekmann, G. Salque, C. Demelas, B. Coulomb, L. Vassalo, S. Ravier, B. Temime-Roussel, D. Voisin, and A. Monod

It has recently been established that unsaturated water-soluble organic compounds (UWSOCs) might efficiently form oligomers in polluted fogs and wet aerosol particles, even for weakly soluble ones like methyl vinyl ketone (MVK). The atmospheric relevance of these processes is explored by means of multiphase process model studies in a companion paper. In the present study, we investigate the aging of these aqueous-phase MVK oligomers formed via OH oxidation, as well as their ability to form secondary organic aerosol (SOA) upon water evaporation. The comparison between aqueous-phase composition and aerosol composition after nebulization of the corresponding solutions shows similar trends for oligomer formation and aging. The measurements reveal that oligomer aging leads to the formation of organic diacids. Quantification of the SOA mass formed after nebulization is performed, and the obtained SOA mass yields seem to depend on the spectral irradiance of the light used to initiate the photochemistry. Investigating a large range of initial MVK concentrations (0.2–20 mM), the results show that their OH oxidation undergoes competition between functionalization and oligomerization that is dependent on the precursor concentration. At high initial MVK concentrations (≥ 2 mM), oligomerization prevails over functionalization, while at lower initial concentrations, oligomerization is not the major process, and functionalization dominates, resulting in small carbonyls, dicarbonyls and monoacids. The atmospheric implications of these processes are discussed.

Posted on 7 January 2015 | 12:00 am


Seasonal characteristics of fine particulate matter (PM) based on high-resolution time-of-flight aerosol mass spectrometric (HR-ToF-AMS) measurements at the HKUST Supersite in Hong Kong

Seasonal characteristics of fine particulate matter (PM) based on high-resolution time-of-flight aerosol mass spectrometric (HR-ToF-AMS) measurements at the HKUST Supersite in Hong Kong

Atmospheric Chemistry and Physics, 15, 37-53, 2015

Author(s): Y. J. Li, B. P. Lee, L. Su, J. C. H. Fung, and C.K. Chan

Atmospheric particulate matter (PM) remains poorly understood due to the lack of comprehensive measurements at high time resolution for tracking its dynamic features and the lack of long-term observation for tracking its seasonal variability. Here, we present highly time-resolved and seasonal compositions and characteristics of non-refractory components in PM with a diameter less than 1 ?m (NR-PM1) at a suburban site in Hong Kong. The measurements were made with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) at the Hong Kong University of Science and Technology (HKUST) Air Quality Research Supersite for 4 months, with one in each season of the year. The average NR-PM1 concentration of ~ 15 ?g m?3 is higher than those AMS measurements made in South Korea and Japan, but lower than those in North China, the Yangtze River Delta and the nearby Pearl River Delta. The seasonal dependence of the total NR-PM1 monthly averaged concentrations was small, but that of the fractions of the species in NR-PM1 was significant. Site characteristic plays an important role in the relative fractions of species in NR-PM1 and our results are generally consistent with measurements at other non-urban sites in this regard. Detailed analyses were conducted on the AMS data in the aspects of (1) species concentrations, (2) size distributions, (3) degree of oxygenation of organics, and (4) positive matrix factorization (PMF)-resolved organic factors in a seasonal context, as well as with air mass origin from back-trajectory analysis. Sulfate had the highest fraction in NR-PM1 (> 40%), and the surrogates of secondary organic species – semi-volatile oxygenated organic aerosol (SVOOA) and low-volatility oxygenated organic aerosol (LVOOA) – prevailed (~ 80%) in the organic portion of NR-PM1. Local contributions to the organic portion of NR-PM1 at this suburban site was strongly dependent on season. The hydrocarbon-like organic aerosol (HOA) factor related to local traffic emissions contributed > 10% to organic aerosols in spring and summer but only 6–7% in autumn and winter. The cooking organic aerosol (COA) factor contributed > 10% to organic aerosols in winter. With the aid of highly time-resolved data, diurnal patterns of the degree of oxygenation of organic aerosols were used to determine the sources and formation processes of the least understood organic portion of PM. The oxygen-to-carbon atomic ratio (O : C) and average carbon oxidation state OS C) showed little variation in autumn and winter, when the long-range transport of oxidized organics dominated, whereas they peaked in the afternoon in spring and summer, when locally produced secondary organic aerosol prevailed. Air mass origin, in contrast, had a strong influence on both NR-PM1 concentrations and the fractions of species in NR-PM1. The findings of the current study provide a better understanding of the role of air mass origin in the seasonal characteristics of the PM composition and the relative importance of local vs. transported organic aerosols in this region.

Posted on 7 January 2015 | 12:00 am


Corrigendum to "Secondary organic aerosol formation exceeds primary particulate matter emissions for light-duty gasoline vehicles" published in Atmos. Chem. Phys., 14, 4661–4678, 2014

Corrigendum to "Secondary organic aerosol formation exceeds primary particulate matter emissions for light-duty gasoline vehicles" published in Atmos. Chem. Phys., 14, 4661–4678, 2014

Atmospheric Chemistry and Physics, 15, 19-20, 2015

Author(s): T. D. Gordon, A. A. Presto, A. A. May, N. T. Nguyen, E. M. Lipsky, N. M. Donahue, A. Gutierrez, M. Zhang, C. Maddox, P. Rieger, S. Chattopadhyay, H. Maldonado, M. M. Maricq, and A. L. Robinson

No abstract available.

Posted on 7 January 2015 | 12:00 am


On the composition of ammonia–sulfuric-acid ion clusters during aerosol particle formation

On the composition of ammonia–sulfuric-acid ion clusters during aerosol particle formation

Atmospheric Chemistry and Physics, 15, 55-78, 2015

Author(s): S. Schobesberger, A. Franchin, F. Bianchi, L. Rondo, J. Duplissy, A. Kürten, I. K. Ortega, A. Metzger, R. Schnitzhofer, J. Almeida, A. Amorim, J. Dommen, E. M. Dunne, M. Ehn, S. Gagné, L. Ickes, H. Junninen, A. Hansel, V.-M. Kerminen, J. Kirkby, A. Kupc, A. Laaksonen, K. Lehtipalo, S. Mathot, A. Onnela, T. Petäjä, F. Riccobono, F. D. Santos, M. Sipilä, A. Tomé, G. Tsagkogeorgas, Y. Viisanen, P. E. Wagner, D. Wimmer, J. Curtius, N. M. Donahue, U. Baltensperger, M. Kulmala, and D. R. Worsnop

The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new-particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH3) and sulfuric acid (H2SO4). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH3–H2SO4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH3] in the range from < 2 to 1400 pptv, [H2SO4] from 3.3 × 106 to 1.4 × 109 cm?3 (0.1 to 56 pptv), and a temperature range from ?25 to +20 °C. Negatively and positively charged clusters were directly measured by an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer, as they initially formed from gas-phase NH3 and H2SO4, and then grew to larger clusters containing more than 50 molecules of NH3 and H2SO4, corresponding to mobility-equivalent diameters greater than 2 nm. Water molecules evaporate from these clusters during sampling and are not observed. We found that the composition of the NH3–H2SO4 clusters is primarily determined by the ratio of gas-phase concentrations [NH3] / [H2SO4], as well as by temperature. Pure binary H2O–H2SO4 clusters (observed as clusters of only H2SO4) only form at [NH3] / [H2SO4] < 0.1 to 1. For larger values of [NH3] / [H2SO4], the composition of NH3–H2SO4 clusters was characterized by the number of NH3 molecules m added for each added H2SO4 molecule n (Δm/Δ n), where n is in the range 4–18 (negatively charged clusters) or 1–17 (positively charged clusters). For negatively charged clusters, Δ m/Δn saturated between 1 and 1.4 for [NH3] / [H2SO4] > 10. Positively charged clusters grew on average by Δm/Δn = 1.05 and were only observed at sufficiently high [NH3] / [H2SO4]. The H2SO4 molecules of these clusters are partially neutralized by NH3, in close resemblance to the acid–base bindings of ammonium bisulfate. Supported by model simulations, we substantiate previous evidence for acid–base reactions being the essential mechanism behind the formation of these clusters under atmospheric conditions and up to sizes of at least 2 nm. Our results also suggest that electrically neutral NH3–H2SO4 clusters, unobservable in this study, have generally the same composition as ionic clusters for [NH3] / [H2SO4] > 10. We expect that NH3–H2SO4 clusters form and grow also mostly by Δm/Δn > 1 in the atmosphere's boundary layer, as [NH3] / [H2SO4] is mostly larger than 10. We compared our results from CLOUD with APi-TOF measurements of NH3–H2SO4 anion clusters during new-particle formation in the Finnish boreal forest. However, the exact role of NH3–H2SO4 clusters in boundary layer particle formation remains to be resolved.

Posted on 7 January 2015 | 12:00 am


The effect of dry and wet deposition of condensable vapors on secondary organic aerosols concentrations over the continental US

The effect of dry and wet deposition of condensable vapors on secondary organic aerosols concentrations over the continental US

Atmospheric Chemistry and Physics, 15, 1-18, 2015

Author(s): C. Knote, A. Hodzic, and J. L. Jimenez

The effect of dry and wet deposition of semi-volatile organic compounds (SVOCs) in the gas phase on the concentrations of secondary organic aerosol (SOA) is reassessed using recently derived water solubility information. The water solubility of SVOCs was implemented as a function of their volatility distribution within the WRF-Chem regional chemistry transport model, and simulations were carried out over the continental United States for the year 2010. Results show that including dry and wet removal of gas-phase SVOCs reduces annual average surface concentrations of anthropogenic and biogenic SOA by 48 and 63% respectively over the continental US. Dry deposition of gas-phase SVOCs is found to be more effective than wet deposition in reducing SOA concentrations (?40 vs. ?8% for anthropogenics, and ?52 vs. ?11% for biogenics). Reductions for biogenic SOA are found to be higher due to the higher water solubility of biogenic SVOCs. The majority of the total mass of SVOC + SOA is actually deposited via the gas phase (61% for anthropogenics and 76% for biogenics). Results are sensitive to assumptions made in the dry deposition scheme, but gas-phase deposition of SVOCs remains crucial even under conservative estimates. Considering reactivity of gas-phase SVOCs in the dry deposition scheme was found to be negligible. Further sensitivity studies where we reduce the volatility of organic matter show that consideration of gas-phase SVOC removal still reduces average SOA concentrations by 31% on average. We consider this a lower bound for the effect of gas-phase SVOC removal on SOA concentrations. A saturation effect is observed for Henry's law constants above 108 M atm?1, suggesting an upper bound of reductions in surface level SOA concentrations by 60% through removal of gas-phase SVOCs. Other models that do not consider dry and wet removal of gas-phase SVOCs would hence overestimate SOA concentrations by roughly 50%. Assumptions about the water solubility of SVOCs made in some current modeling systems (H* = H* (CH3COOH); H* = 105 M atm?1; H* = H* (HNO3)) still lead to an overestimation of 35%/25%/10% compared to our best estimate.

Posted on 6 January 2015 | 12:00 am





Other notes:



 Information about this site:


 
The author- or copyrights of the listed Internet pages are held by the respective authors or site operators, who are also responsible for the content of the presentations.
 
To see your page listed here: Send us an eMail! Condition: Subject-related content on chemistry, biochemistry and comparable academic disciplines!
Citation:
http://www.internetchemistry.com/rss/atmospheric-chemistry.php
Keywords:
Chronological list of recent articles on Chemistry, Atmospheric Chemistry, Atmospheric Chemistry and Physics.
Update:
28.09.2013


Internetchemistry ChemLin © 1996 - 2013 A. J.