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Atmospheric Chemistry and Physics - Current Research Articles



Current research articles: Atmospheric Chemistry

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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:



Impacts of changes in land use and land cover on atmospheric chemistry and air quality over the 21st century

Impacts of changes in land use and land cover on atmospheric chemistry and air quality over the 21st century

Atmospheric Chemistry and Physics, 12, 1597-1609, 2012

Author(s): S. Wu, L. J. Mickley, J. O. Kaplan, and D. J. Jacob

The effects of future land use and land cover change on the chemical composition of the atmosphere and air quality are largely unknown. To investigate the potential effects associated with future changes in vegetation driven by atmospheric CO2 concentrations, climate, and anthropogenic land use over the 21st century, we performed a series of model experiments combining a general circulation model with a dynamic global vegetation model and an atmospheric chemical-transport model. Our results indicate that climate- and CO2-induced changes in vegetation composition and density between 2100 and 2000 could lead to decreases in summer afternoon surface ozone of up to 10 ppb over large areas of the northern mid-latitudes. This is largely driven by the substantial increases in ozone dry deposition associated with increases in vegetation density in a warmer climate with higher atmospheric CO2 abundance. Climate-driven vegetation changes over the period 2000–2100 lead to general increases in isoprene emissions, globally by 15% in 2050 and 36% in 2100. These increases in isoprene emissions result in decreases in surface ozone concentrations where the NOx levels are low, such as in remote tropical rainforests. However, over polluted regions, such as the northeastern United States, ozone concentrations are calculated to increase with higher isoprene emissions in the future. Increases in biogenic emissions also lead to higher concentrations of secondary organic aerosols, which increase globally by 10% in 2050 and 20% in 2100. Summertime surface concentrations of secondary organic aerosols are calculated to increase by up to 1 ?g m?3 and double for large areas in Eurasia over the period of 2000–2100. When we use a scenario of future anthropogenic land use change, we find less increase in global isoprene emissions due to replacement of higher-emitting forests by lower-emitting cropland. The global atmospheric burden of secondary organic aerosols changes little by 2100 when we account for future land use change, but both secondary organic aerosols and ozone show large regional changes at the surface.

Posted on 14 February 2012 | 12:00 am


The isotopic composition of precipitation from a winter storm – a case study with the limited-area model COSMOiso

The isotopic composition of precipitation from a winter storm – a case study with the limited-area model COSMOiso

Atmospheric Chemistry and Physics, 12, 1629-1648, 2012

Author(s): S. Pfahl, H. Wernli, and K. Yoshimura

Stable water isotopes are valuable tracers of the atmospheric water cycle, and potentially provide useful information also on weather-related processes. In order to further explore this potential, the water isotopes H218O and HDO are incorporated into the limited-area model COSMO. In a first case study, the new COSMOiso model is used for simulating a winter storm event in January 1986 over the eastern United States associated with intense frontal precipitation. The modelled isotope ratios in precipitation and water vapour are compared to spatially distributed δ18O observations. COSMOiso very accurately reproduces the statistical distribution of δ18O in precipitation, and also the synoptic-scale spatial pattern and temporal evolution agree well with the measurements. Perpendicular to the front that triggers most of the rainfall during the event, the model simulates a gradient in the isotopic composition of the precipitation, with high δ18O values in the warm air and lower values in the cold sector behind the front. This spatial pattern is created through an interplay of large scale air mass advection, removal of heavy isotopes by precipitation at the front and microphysical interactions between rain drops and water vapour beneath the cloud base. This investigation illustrates the usefulness of high resolution, event-based model simulations for understanding the complex processes that cause synoptic-scale variability of the isotopic composition of atmospheric waters. In future research, this will be particularly beneficial in combination with laser spectrometric isotope observations with high temporal resolution.

Posted on 14 February 2012 | 12:00 am


The Mineral Dust Cycle in EMAC 2.40: sensitivity to the spectral resolution and the dust emission scheme

The Mineral Dust Cycle in EMAC 2.40: sensitivity to the spectral resolution and the dust emission scheme

Atmospheric Chemistry and Physics, 12, 1611-1627, 2012

Author(s): G. Gläser, A. Kerkweg, and H. Wernli

This first detailed analysis of the mineral dust cycle in the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model system investigates the performance of two dust emission schemes, following the approach of Balkanski et al. (2004) and Tegen et al. (2002), respectively, and the influence of the horizontal model resolution. Here the spectral resolutions T42, T63, T85, and T106 are investigated. A basic sulphur chemistry, enabling the coating of insoluble dust particles to make them soluble, is employed in order to realistically describe the ageing and wet deposition of mineral dust. Independent of the dust emission scheme the five-year simulations with the horizontal resolutions T42 and T63 produce unrealistically high emissions at some grid points in the Tarim Basin in Central Asia, leading to very high dust loads in polar regions. With these coarse resolutions, dust source grid points in the basin and elevated grid points of the Himalayas with high wind speeds cannot be distinguished, causing this overestimation. In T85 and T106 these regions are well separated and considerably less dust is emitted there. With the chosen model setup, the dust emission scheme by Balkanski et al. (2004) places the global maximum of emissions in the Thar Desert in India. This is unrealistic as the Sahara Desert is known to be the largest dust source in the world. This is the main deficiency of this scheme compared to the one by Tegen et al. (2002), which, based on a qualitative comparison to AEROCOM data, produces a very reasonable distribution of emissions and dust loads in simulations with resolutions T85 and T106. For future climate simulations with EMAC focusing on mineral dust, we recommend to use the dust emission scheme by Tegen et al. (2002) and a model resolution of at least T85. Simulations of two selected episodes and comparison to observational data sets show that in this model configuration EMAC is able to realistically simulate also intense, episodic events of dust emission and long-range transport.

Posted on 14 February 2012 | 12:00 am


Revised identification of tropical oceanic cumulus congestus as viewed by CloudSat

Revised identification of tropical oceanic cumulus congestus as viewed by CloudSat

Atmospheric Chemistry and Physics, 12, 1587-1595, 2012

Author(s): S. P. F. Casey, E. J. Fetzer, and B. H. Kahn

Congestus cloud convective features are examined in one year of tropical oceanic cloud observations from the CloudSat/CALIPSO instruments. Two types of convective clouds (cumulus and deep convective, based on classification profiles from radar), and associated differences in radar reflectivity and radar/lidar cloud-top height are considered. Congestus convective features are defined as contiguous convective clouds with heights between 3 and 9 km. Three criteria were used in previous studies to identify congestus: (1) CloudSat and CALIPSO cloud-top heights less than 1 km apart; (2) CloudSat 0 dBZ echo-top height less than 1 km from CloudSat cloud-top height, and (3) CloudSat 10 dBZ echo-top height less than 2 km from CloudSat cloud-top height. A majority of congestus convective features satisfy the second and third requirements. However, over 40% of convective features identified had no associated CALIPSO cloud-top height, predominantly due to the extinguishment of the lidar beam above the CloudSat-reported convective cloud. For the remaining cells, approximately 56% of these satisfy all three requirements; when considering the lidar beam-extinction issue, only 31% of congestus convective features are identified using these criteria. This implies that while previous methods used to identify congestus clouds may be accurate in finding vigorous convection (such as transient congestus rising toward the tropopause), these criteria may miss almost 70% of the total observed congestus convective features, suggesting a more general approach should be used to describe congestus and its surrounding environment.

Posted on 13 February 2012 | 12:00 am


Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W)

Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W)

Atmospheric Chemistry and Physics, 12, 1571-1585, 2012

Author(s): K. A. Day, M. J. Taylor, and N. J. Mitchell

Atmospheric temperatures and winds in the mesosphere and lower thermosphere have been measured simultaneously using the Aura satellite and a meteor radar at Bear Lake Observatory (42° N, 111° W), respectively. The data presented in this study is from the interval March 2008 to July 2011.

The mean winds observed in the summer-time over Bear Lake Observatory show the meridional winds to be equatorward at meteor heights during April?August and to reach monthly-mean velocities of ?12 m s?1. The mean winds are closely related to temperatures in this region of the atmosphere and in the summer the coldest mesospheric temperatures occur about the same time as the strongest equatorward meridional winds. The zonal winds are eastward through most of the year and in the summer strong eastward zonal wind shears of up to ~4.5 m s?1 km?1 are present. However, westward winds are observed at the upper heights in winter and sometimes during the equinoxes. Considerable inter-annual variability is observed in the mean winds and temperatures.

Comparisons of the observed winds with URAP and HWM-07 reveal some large differences. Our radar zonal wind observations are generally more eastward than predicted by the URAP model zonal winds. Considering the radar meridional winds, in comparison to HWM-07 our observations reveal equatorward flow at all meteor heights in the summer whereas HWM-07 suggests that only weakly equatorward, or even poleward flows occur at the lower heights. However, the zonal winds observed by the radar and modelled by HWM-07 are generally similar in structure and strength.

Signatures of the 16- and 5-day planetary waves are clearly evident in both the radar-wind data and Aura-temperature data. Short-lived wave events can reach large amplitudes of up to ~15 m s?1 and 8 K and 20 m s?1 and 10 K for the 16- and 5-day waves, respectively. A clear seasonal and short-term variability are observed in the 16- and 5-day planetary wave amplitudes. The 16-day wave reaches largest amplitude in winter and is also present in summer, but with smaller amplitudes. The 5-day wave reaches largest amplitude in winter and in late summer. An inter-annual variability in the amplitude of the planetary waves is evident in the four years of observations. Some 41 episodes of large-amplitude wave occurrence are identified. Temperature and wind amplitudes for these episodes, AT and AW, that passed the Student T-test were found to be related by, AT = 0.34 AW and AT = 0.62 AW for the 16- and 5-day wave, respectively.

Posted on 10 February 2012 | 12:00 am


Observation and modelling of OH and HO2 concentrations in the Pearl River Delta 2006: a missing OH source in a VOC rich atmosphere

Observation and modelling of OH and HO2 concentrations in the Pearl River Delta 2006: a missing OH source in a VOC rich atmosphere

Atmospheric Chemistry and Physics, 12, 1541-1569, 2012

Author(s): K. D. Lu, F. Rohrer, F. Holland, H. Fuchs, B. Bohn, T. Brauers, C. C. Chang, R. Häseler, M. Hu, K. Kita, Y. Kondo, X. Li, S. R. Lou, S. Nehr, M. Shao, L. M. Zeng, A. Wahner, Y. H. Zhang, and A. Hofzumahaus

Ambient OH and HO2 concentrations were measured by laser induced fluorescence (LIF) during the PRIDE-PRD2006 (Program of Regional Integrated Experiments of Air Quality over the Pearl River Delta, 2006) campaign at a rural site downwind of the megacity of Guangzhou in Southern China. The observed OH concentrations reached daily peak values of (15–26) × 106 cm?3 which are among the highest values so far reported for urban and suburban areas. The observed OH shows a consistent high correlation with j(O1D) over a broad range of NOx conditions. The correlation cannot be reproduced by model simulations, indicating that OH stabilizing processes are missing in current models. The observed OH exhibited a weak dependence on NOx in contrast to model predictions. While modelled and measured OH agree well at NO mixing ratios above 1 ppb, a continuously increasing underprediction of the observed OH is found towards lower NO concentrations, reaching a factor of 8 at 0.02 ppb NO. A dependence of the modelled-to-measured OH ratio on isoprene cannot be concluded from the PRD data. However, the magnitude of the ratio fits into the isoprene dependent trend that was reported from other campaigns in forested regions. Hofzumahaus et al. (2009) proposed an unknown OH recycling process without NO, in order to explain the high OH levels at PRD in the presence of high VOC reactivity and low NO. Taking a recently discovered interference in the LIF measurement of HO2 into account, the need for an additional HO2 ? OH recycling process persists, but the required source strength may be up to 20% larger than previously determined. Recently postulated isoprene mechanisms by Lelieveld et al. (2008) and Peeters and Müller (2010) lead to significant enhancements of OH expected for PRD, but an underprediction of the observed OH by a factor of two remains at low NO (0.1–0.2 ppb). If the photolysis of hydroperoxy aldehydes from isoprene is as efficient as proposed by Peeters and Müller (2010), the corresponding OH formation at PRD would be more important than the primary OH production from ozone and HONO. While the new isoprene mechanisms need to be confirmed by laboratory experiments, there is probably need for other, so far unidentified chemical processes to explain entirely the high OH levels observed in Southern China.

Posted on 9 February 2012 | 12:00 am


Atmospheric greenhouse gases retrieved from SCIAMACHY: comparison to ground-based FTS measurements and model results

Atmospheric greenhouse gases retrieved from SCIAMACHY: comparison to ground-based FTS measurements and model results

Atmospheric Chemistry and Physics, 12, 1527-1540, 2012

Author(s): O. Schneising, P. Bergamaschi, H. Bovensmann, M. Buchwitz, J. P. Burrows, N. M. Deutscher, D. W. T. Griffith, J. Heymann, R. Macatangay, J. Messerschmidt, J. Notholt, M. Rettinger, M. Reuter, R. Sussmann, V. A. Velazco, T. Warneke, P. O. Wennberg, and D. Wunch

SCIAMACHY onboard ENVISAT (launched in 2002) enables the retrieval of global long-term column-averaged dry air mole fractions of the two most important anthropogenic greenhouse gases carbon dioxide and methane (denoted XCO2 and XCH4). In order to assess the quality of the greenhouse gas data obtained with the recently introduced v2 of the scientific retrieval algorithm WFM-DOAS, we present validations with ground-based Fourier Transform Spectrometer (FTS) measurements and comparisons with model results at eight Total Carbon Column Observing Network (TCCON) sites providing realistic error estimates of the satellite data. Such validation is a prerequisite to assess the suitability of data sets for their use in inverse modelling.

It is shown that there are generally no significant differences between the carbon dioxide annual increases of SCIAMACHY and the assimilation system CarbonTracker (2.00 ± 0.16 ppm yr?1 compared to 1.94 ± 0.03 ppm yr?1 on global average). The XCO2 seasonal cycle amplitudes derived from SCIAMACHY are typically larger than those from TCCON which are in turn larger than those from CarbonTracker. The absolute values of the northern hemispheric TCCON seasonal cycle amplitudes are closer to SCIAMACHY than to CarbonTracker and the corresponding differences are not significant when compared with SCIAMACHY, whereas they can be significant for a subset of the analysed TCCON sites when compared with CarbonTracker. At Darwin we find discrepancies of the seasonal cycle derived from SCIAMACHY compared to the other data sets which can probably be ascribed to occurrences of undetected thin clouds. Based on the comparison with the reference data, we conclude that the carbon dioxide data set can be characterised by a regional relative precision (mean standard deviation of the differences) of about 2.2 ppm and a relative accuracy (standard deviation of the mean differences) of 1.1–1.2 ppm for monthly average composites within a radius of 500 km.

For methane, prior to November 2005, the regional relative precision amounts to 12 ppb and the relative accuracy is about 3 ppb for monthly composite averages within the same radius. The loss of some spectral detector pixels results in a degradation of performance thereafter in the spectral range currently used for the methane column retrieval. This leads to larger scatter and lower XCH4 values are retrieved in the tropics for the subsequent time period degrading the relative accuracy. As a result, the overall relative precision is estimated to be 17 ppb and the relative accuracy is in the range of about 10–20 ppb for monthly averages within a radius of 500 km.

The derived estimates show that the SCIAMACHY XCH4 data set before November 2005 is suitable for regional source/sink determination and regional-scale flux uncertainty reduction via inverse modelling worldwide. In addition, the XCO2 monthly data potentially provide valuable information in continental regions, where there is sparse sampling by surface flask measurements.

Posted on 9 February 2012 | 12:00 am


Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China

Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China

Atmospheric Chemistry and Physics, 12, 1497-1513, 2012

Author(s): X. Li, T. Brauers, R. Häseler, B. Bohn, H. Fuchs, A. Hofzumahaus, F. Holland, S. Lou, K. D. Lu, F. Rohrer, M. Hu, L. M. Zeng, Y. H. Zhang, R. M. Garland, H. Su, A. Nowak, A. Wiedensohler, N. Takegawa, M. Shao, and A. Wahner

We performed measurements of nitrous acid (HONO) during the PRIDE-PRD2006 campaign in the Pearl River Delta region 60 km north of Guangzhou, China, for 4 weeks in June 2006. HONO was measured by a LOPAP in-situ instrument which was setup in one of the campaign supersites along with a variety of instruments measuring hydroxyl radicals, trace gases, aerosols, and meteorological parameters. Maximum diurnal HONO mixing ratios of 1–5 ppb were observed during the nights. We found that the nighttime build-up of HONO can be attributed to the heterogeneous NO2 to HONO conversion on ground surfaces and the OH + NO reaction. In addition to elevated nighttime mixing ratios, measured noontime values of ?200 ppt indicate the existence of a daytime source higher than the OH + NO?HONO reaction. Using the simultaneously recorded OH, NO, and HONO photolysis frequency, a daytime additional source strength of HONO (PM) was calculated to be 0.77 ppb h?1 on average. This value compares well to previous measurements in other environments. Our analysis of PM provides evidence that the photolysis of HNO3 adsorbed on ground surfaces contributes to the HONO formation.

Posted on 8 February 2012 | 12:00 am


Corrigendum to "Simulated enhancement of ENSO-related rainfall variability due to Australian dust" published in Atmos. Chem. Phys., 11, 6575–6592, 2011

Corrigendum to "Simulated enhancement of ENSO-related rainfall variability due to Australian dust" published in Atmos. Chem. Phys., 11, 6575–6592, 2011

Atmospheric Chemistry and Physics, 12, 1481-1481, 2012

Author(s): L. D. Rotstayn, M. A. Collier, R. M. Mitchell, Y. Qin, S. K. Campbell, and S. M. Dravitzki

No abstract available.

Posted on 8 February 2012 | 12:00 am


Corrigendum to "Accumulation of aerosols over the Indo-Gangetic plains and southern slopes of the Himalayas: distribution, properties and radiative effects during the 2009 pre-monsoon season" published in Atmos. Chem. Phys., 11, 12841–12863, 2011

Corrigendum to "Accumulation of aerosols over the Indo-Gangetic plains and southern slopes of the Himalayas: distribution, properties and radiative effects during the 2009 pre-monsoon season" published in Atmos. Chem. Phys., 11, 12841–12863, 2011

Atmospheric Chemistry and Physics, 12, 1525-1525, 2012

Author(s): R. Gautam, N. C. Hsu, S. C. Tsay, K. M. Lau, B. Holben, S. Bell, A. Smirnov, C. Li, R. Hansell, Q. Ji, S. Payra, D. Aryal, R. Kayastha, and K. M. Kim

No abstract available.

Posted on 8 February 2012 | 12:00 am


Formation of 3-methyl-1,2,3-butanetricarboxylic acid via gas phase oxidation of pinonic acid – a mass spectrometric study of SOA aging

Formation of 3-methyl-1,2,3-butanetricarboxylic acid via gas phase oxidation of pinonic acid – a mass spectrometric study of SOA aging

Atmospheric Chemistry and Physics, 12, 1483-1496, 2012

Author(s): L. Müller, M.-C. Reinnig, K. H. Naumann, H. Saathoff, T. F. Mentel, N. M. Donahue, and T. Hoffmann

This paper presents the results of mass spectrometric investigations of the OH-initiated oxidative aging of ?-pinene SOA under simulated tropospheric conditions at the large aerosol chamber facility AIDA, Karlsruhe Institute of Technology. In particular, the OH-initiated oxidation of pure pinic and pinonic acid, two well-known oxidation products of ?-pinene, was investigated. Two complementary analytical techniques were used, on-line atmospheric pressure chemical ionization/mass spectrometry (APCI/MS) and filter sampling followed by liquid chromatography/mass spectrometry (LC/ESI-MS). The results show that 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), a very low volatile ?-pinene SOA product and a tracer compound for terpene SOA, is formed from the oxidation of pinonic acid and that this oxidation takes place in the gas phase. This finding is confirmed by temperature-dependent aging experiments on whole SOA formed from ?-pinene, in which the yield of MBTCA scales with the pinonic acid fraction in the gas phase. Based on the results, several feasible gas-phase radical mechanisms are discussed to explain the formation of MBTCA from OH-initiated pinonic acid oxidation.

Posted on 8 February 2012 | 12:00 am


Air pollution control and decreasing new particle formation lead to strong climate warming

Air pollution control and decreasing new particle formation lead to strong climate warming

Atmospheric Chemistry and Physics, 12, 1515-1524, 2012

Author(s): R. Makkonen, A. Asmi, V.-M. Kerminen, M. Boy, A. Arneth, P. Hari, and M. Kulmala

The number concentration of cloud droplets determines several climatically relevant cloud properties. A major cause for the high uncertainty in the indirect aerosol forcing is the availability of cloud condensation nuclei (CCN), which in turn is highly sensitive to atmospheric new particle formation. Here we present the effect of new particle formation on anthropogenic aerosol forcing in present-day (year 2000) and future (year 2100) conditions. The present-day total aerosol forcing is increased from ?1.0 W m?2 to ?1.6 W m?2 when nucleation is introduced into the model. Nucleation doubles the change in aerosol forcing between years 2000 and 2100, from +0.6 W m?2 to +1.4 W m?2. Two climate feedbacks are studied, resulting in additional negative forcings of ?0.1 W m?2 (+10% DMS emissions in year 2100) and ?0.5 W m?2 (+50% BVOC emissions in year 2100). With the total aerosol forcing diminishing in response to air pollution control measures taking effect, warming from increased greenhouse gas concentrations can potentially increase at a very rapid rate.

Posted on 8 February 2012 | 12:00 am


Modeling the climate impact of road transport, maritime shipping and aviation over the period 1860–2100 with an AOGCM

Modeling the climate impact of road transport, maritime shipping and aviation over the period 1860–2100 with an AOGCM

Atmospheric Chemistry and Physics, 12, 1449-1480, 2012

Author(s): D. J. L. Olivié, D. Cariolle, H. Teyssèdre, D. Salas, A. Voldoire, H. Clark, D. Saint-Martin, M. Michou, F. Karcher, Y. Balkanski, M. Gauss, O. Dessens, B. Koffi, and R. Sausen

For the period 1860–2100 (SRES scenario A1B for 2000–2100), the impact of road transport, maritime shipping and aviation on climate is studied using an Atmosphere Ocean General Circulation Model (AOGCM). In addition to carbon dioxide (CO2) emissions from these transport sectors, most of their non-CO2 emissions are also taken into account, i.e. the forcing from ozone, methane, black carbon, organic carbon, sulfate, CFC-12 and HFC-134a from air conditioning systems in cars, and contrails. For the year 2000, the CO2 emissions from all sectors together induce a global annual-mean surface air temperature increase of around 0.1 K. In 2100, the CO2 emissions from road transport induce a global mean warming of 0.3 K, while shipping and aviation each contribute 0.1 K. For road transport, the non-CO2 impact is largest between 2000 and 2050 (of the order of 0.1 K) becoming smaller at the end of the 21st century. The non-CO2 impact from shipping is negative, reaching ?0.1 K between 2050 and 2100, while for aviation it is positive and its estimate varies between 0 and 0.15 K in 2100. The largest changes in sea-level from thermal expansion in 2000 are 1.6 mm for the CO2 emissions from road transport, and around ?3 mm from the non-CO2 effects of shipping. In 2100, sea-level rises by 18 mm due to the CO2 emissions from road transport and by 4.6 mm due to shipping or aviation CO2 emissions. Non-CO2 changes are of the order of 1 mm for road transport, ?6.6 mm for shipping, and the estimate for aviation varies between ?1.2 and 4.3 mm. When focusing on the geographical distribution, the non-CO2 impact from road transport and shipping on the surface air temperature is only slightly stronger in northern than in southern mid-latitudes, while the impact from aviation can be a factor of 5 stronger in the northern than in the southern hemisphere. Further it is observed that most of the impacts are more pronounced at high latitudes, and that the non-CO2 emissions from aviation strongly impact the NAO index. The impacts on the oceanic meridional overturning circulation and the Niño3.4 index are also quantified.

Posted on 7 February 2012 | 12:00 am


Bromine and iodine chemistry in a global chemistry-climate model: description and evaluation of very short-lived oceanic sources

Bromine and iodine chemistry in a global chemistry-climate model: description and evaluation of very short-lived oceanic sources

Atmospheric Chemistry and Physics, 12, 1423-1447, 2012

Author(s): C. Ordóñez, J.-F. Lamarque, S. Tilmes, D. E. Kinnison, E. L. Atlas, D. R. Blake, G. Sousa Santos, G. Brasseur, and A. Saiz-Lopez

The global chemistry-climate model CAM-Chem has been extended to incorporate an expanded bromine and iodine chemistry scheme that includes natural oceanic sources of very short-lived (VSL) halocarbons, gas-phase photochemistry and heterogeneous reactions on aerosols. Ocean emissions of five VSL bromocarbons (CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl) and three VSL iodocarbons (CH2ICl, CH2IBr, CH2I2) have been parameterised by a biogenic chlorophyll-a (chl-a) dependent source in the tropical oceans (20° N–20° S). Constant oceanic fluxes with 2.5 coast-to-ocean emission ratios are separately imposed on four different latitudinal bands in the extratropics (20°–50° and above 50° in both hemispheres). Top-down emission estimates of bromocarbons have been derived using available measurements in the troposphere and lower stratosphere, while iodocarbons have been constrained with observations in the marine boundary layer (MBL). Emissions of CH3I are based on a previous inventory and the longer lived CH3Br is set to a surface mixing ratio boundary condition. The global oceanic emissions estimated for the most abundant VSL bromocarbons – 533 Gg yr?1 for CHBr3 and 67.3 Gg yr?1 for CH2Br2 – are within the range of previous estimates. Overall the latitudinal and vertical distributions of modelled bromocarbons are in good agreement with observations. Nevertheless, we identify some issues such as the reduced number of aircraft observations to validate models in the Southern Hemisphere, the overestimation of CH2Br2 in the upper troposphere – lower stratosphere and the underestimation of CH3I in the same region. Despite the difficulties involved in the global modelling of the shortest lived iodocarbons (CH2ICl, CH2IBr, CH2I2), modelled results are in good agreement with published observations in the MBL. Finally, sensitivity simulations show that knowledge of the diurnal emission cycle for these species, in particular for CH2I2, is key to assess their global source strength.

Posted on 7 February 2012 | 12:00 am


Evolution of trace gases and particles emitted by a chaparral fire in California

Evolution of trace gases and particles emitted by a chaparral fire in California

Atmospheric Chemistry and Physics, 12, 1397-1421, 2012

Author(s): S. K. Akagi, J. S. Craven, J. W. Taylor, G. R. McMeeking, R. J. Yokelson, I. R. Burling, S. P. Urbanski, C. E. Wold, J. H. Seinfeld, H. Coe, M. J. Alvarado, and D. R. Weise

Biomass burning (BB) is a major global source of trace gases and particles. Accurately representing the production and evolution of these emissions is an important goal for atmospheric chemical transport models. We measured a suite of gases and aerosols emitted from an 81 hectare prescribed fire in chaparral fuels on the central coast of California, US on 17 November 2009. We also measured physical and chemical changes that occurred in the isolated downwind plume in the first ~4 h after emission. The measurements were carried out onboard a Twin Otter aircraft outfitted with an airborne Fourier transform infrared spectrometer (AFTIR), aerosol mass spectrometer (AMS), single particle soot photometer (SP2), nephelometer, LiCor CO2 analyzer, a chemiluminescence ozone instrument, and a wing-mounted meteorological probe. Our measurements included: CO2; CO; NOx; NH3; non-methane organic compounds; organic aerosol (OA); inorganic aerosol (nitrate, ammonium, sulfate, and chloride); aerosol light scattering; refractory black carbon (rBC); and ambient temperature, relative humidity, barometric pressure, and three-dimensional wind velocity. The molar ratio of excess O3 to excess CO in the plume (?O3/?CO) increased from ?5.13 (±1.13) × 10?3 to 10.2 (±2.16) × 10?2 in ~4.5 h following smoke emission. Excess acetic and formic acid (normalized to excess CO) increased by factors of 1.73 ± 0.43 and 7.34 ± 3.03 (respectively) over the same time since emission. Based on the rapid decay of C2H4 we infer an in-plume average OH concentration of 5.27 (±0.97) × 106 molec cm?3, consistent with previous studies showing elevated OH concentrations in biomass burning plumes. Ammonium, nitrate, and sulfate all increased over the course of 4 h. The observed ammonium increase was a factor of 3.90 ± 2.93 in about 4 h, but accounted for just ~36% of the gaseous ammonia lost on a molar basis. Some of the gas phase NH3 loss may have been due to condensation on, or formation of, particles below the AMS detection range. NOx was converted to PAN and particle nitrate with PAN production being about two times greater than production of observable nitrate in the first ~4 h following emission. The excess aerosol light scattering in the plume (normalized to excess CO2) increased by a factor of 2.50 ± 0.74 over 4 h. The increase in light scattering was similar to that observed in an earlier study of a biomass burning plume in Mexico where significant secondary formation of OA closely tracked the increase in scattering. In the California plume, however, ?OA/?CO2 decreased sharply for the first hour and then increased slowly with a net decrease of ~20% over 4 h. The fraction of thickly coated rBC particles increased up to ~85% over the 4 h aging period. Decreasing OA accompanied by increased scattering/particle coating in initial aging may be due to a combination of particle coagulation and evaporation processes. Recondensation of species initially evaporated from the particles may have contributed to the subsequent slow rise in OA. We compare our results to observations from other plume aging studies and suggest that differences in environmental factors such as smoke concentration, oxidant concentration, actinic flux, and RH contribute significantly to the variation in plume evolution observations.

Posted on 7 February 2012 | 12:00 am


Spatial and seasonal variability of PM2.5 acidity at two Chinese megacities: insights into the formation of secondary inorganic aerosols

Spatial and seasonal variability of PM2.5 acidity at two Chinese megacities: insights into the formation of secondary inorganic aerosols

Atmospheric Chemistry and Physics, 12, 1377-1395, 2012

Author(s): K. He, Q. Zhao, Y. Ma, F. Duan, F. Yang, Z. Shi, and G. Chen

Aerosol acidity is one of the most important parameters influencing atmospheric chemistry and physics. Based on continuous field observations from January 2005 to May 2006 and thermodynamic modeling, we investigated the spatial and seasonal variations in PM2.5 acidity in two megacities in China, Beijing and Chongqing. Spatially, PM2.5 was generally more acidic in Chongqing than in Beijing, but a reverse spatial pattern was found within the two cities, with more acidic PM2.5 at the urban site in Beijing whereas the rural site in Chongqing. Ionic compositions of PM2.5 revealed that it was the higher concentrations of NO3 at the urban site in Beijing and the lower concentrations of Ca2+ within the rural site in Chongqing that made their PM2.5 more acidic. Temporally, PM2.5 was more acidic in summer and fall than in winter, while in the spring of 2006, the acidity of PM2.5 was higher in Beijing but lower in Chongqing than that in 2005. These were attributed to the more efficient formation of nitrate relative to sulfate as a result of the influence of Asian desert dust in 2006 in Beijing and the greater wet deposition of ammonium compared to sulfate and nitrate in 2005 in Chongqing. Furthermore, simultaneous increase of PM2.5 acidity was observed from spring to early summer of 2005 in both cities. This synoptic-scale evolution of PM2.5 acidity was accompanied by the changes in air masses origins, which were influenced by the movements of a subtropical high over the northwestern Pacific in early summer. Finally, the correlations between [NO3]/[SO42−] and [NH4+]/[SO42−] suggests that under conditions of high aerosol acidity, heterogeneous reactions became one of the major pathways for the formation of nitrate at both cities. These findings provided new insights in our understanding of the spatial and temporal variations in aerosol acidity in Beijing and Chongqing, as well as those reported in other cities in China.

Posted on 6 February 2012 | 12:00 am


Seasonal variations of stable carbon isotopic composition and biogenic tracer compounds of water-soluble organic aerosols in a deciduous forest

Seasonal variations of stable carbon isotopic composition and biogenic tracer compounds of water-soluble organic aerosols in a deciduous forest

Atmospheric Chemistry and Physics, 12, 1367-1376, 2012

Author(s): Y. Miyazaki, P. Q. Fu, K. Kawamura, Y. Mizoguchi, and K. Yamanoi

To investigate the seasonal changes in biogenic water-soluble organic carbon (WSOC) aerosols in a boreal forest, aerosol samples were collected continuously in the canopy of a deciduous forest in northern Japan during 2009–2010. Stable carbon isotopic composition of WSOC (δ13CWSOC) in total suspended particulate matter (TSP) exhibited a distinct seasonal cycle, with lower values from June through September (?25.5±0.5 ‰). This cycle follows the net CO2 exchange between the forest ecosystem and the atmosphere, indicating that δ13CWSOC likely reflects the biological activity at the forest site. WSOC concentrations showed the highest values in early summer and autumn. Positive matrix factorization (PMF) analysis indicated that the factor in which biogenic secondary organic aerosols (BSOAs) dominated accounted for ~40 % of the highest concentrations of WSOC, where BSOAs mostly consisted of ?-/?-pinene SOA. In addition, primary biological aerosol particles (PBAPs) made similar contributions (~57 %) to the WSOC near the forest floor in early summer. This finding indicates that the production of both primary and secondary WSOC aerosols is important during the growing season in a deciduous forest. The methanesulfonic acid (MSA) maximum was also found in early summer and had a distinct vertical gradient with larger concentrations near the forest floor. Together with the similar vertical gradients found for WSOC and δ13CWSOC as well as the ?-/?-pinene SOA tracers, our results indicate that the forest floor, including ground vegetation and soil, acts as a significant source of WSOC in TSP within a forest canopy at the study site.

Posted on 3 February 2012 | 12:00 am


ClOOCl photolysis at high solar zenith angles: analysis of the RECONCILE self-match flight

ClOOCl photolysis at high solar zenith angles: analysis of the RECONCILE self-match flight

Atmospheric Chemistry and Physics, 12, 1353-1365, 2012

Author(s): O. Sumi?ska-Ebersoldt, R. Lehmann, T. Wegner, J.-U. Grooß, E. Hösen, R. Weigel, W. Frey, S. Griessbach, V. Mitev, C. Emde, C. M. Volk, S. Borrmann, M. Rex, F. Stroh, and M. von Hobe

The photolysis rate constant of dichlorine peroxide (ClOOCl, ClO dimer) JClOOCl is a critical parameter in catalytic cycles destroying ozone (O3) in the polar stratosphere. In the atmospherically relevant wavelength region (? > 310 nm), significant discrepancies between laboratory measurements of ClOOCl absorption cross sections and spectra cause a large uncertainty in JClOOCl. Previous investigations of the consistency of published JClOOCl with atmospheric observations of chlorine monoxide (ClO) and ClOOCl have focused on the photochemical equilibrium between ClOOCl formation and photolysis, and thus could only constrain the ratio of JClOOCl over the ClOOCl formation rate constant krec. Here, we constrain the atmospherically effective JClOOCl independent of krec, using ClO measured in the same air masses before and directly after sunrise during an aircraft flight that was part of the RECONCILE field campaign in the winter 2010 from Kiruna, Sweden. Over sunrise, when the ClO/ClOOCl system comes out of thermal equilibrium and the influence of the ClO recombination reaction is negligible, the increase in ClO concentrations is significantly faster than expected from JClOOCl based on the absorption spectrum proposed by Pope et al. (2007), but does not warrant cross sections larger than recently published values by Papanastasiou et al. (2009). In particular, the existence of a significant ClOOCl absorption band longwards of 420 nm is not supported by our observations. The observed night-time ClO would not be consistent with a ClO/ClOOCl thermal equilibrium constant significantly higher than the one proposed by Plenge et al. (2005).

Posted on 2 February 2012 | 12:00 am


Does acetone react with HO2 in the upper-troposphere?

Does acetone react with HO2 in the upper-troposphere?

Atmospheric Chemistry and Physics, 12, 1339-1351, 2012

Author(s): T. J. Dillon, A. Pozzer, L. Vereecken, J. N. Crowley, and J. Lelieveld

Recent theoretical calculations showed that reaction with HO2 could be an important sink for acetone (CH3C(O)CH3) and source of acetic acid (CH3C(O)OH) in cold parts of the atmosphere (e.g. the tropopause region). This work details studies of HO2 + CH3C(O)CH3 (CH3)2C(OH)OO (R1) in laboratory-based and theoretical chemistry experiments; the atmospheric significance of Reaction (R1) was assessed in a global 3-D chemical model. Pulsed laser-kinetic experiments were conducted, for the first time, at the low-temperatures representative of the tropopause. Reaction with NO converted HO2 to OH for detection by laser induced fluorescence. Reduced yields of OH at T < 220 K provided indirect evidence for the sequestration of HO2 by CH3C(O)CH3 with a forward rate coefficient greater than 2 × 10−12 cm3 molecule?1 s?1. No evidence for Reaction (R1) was observed at T > 230 K, probably due to rapid thermal dissociation back to HO2 + CH3C(O)CH3. Numerical simulations of the data indicate that these experiments were sensitive to only (R1a) HO2-CH3C(O)CH3 complex formation, the first step in (R1). Rearrangement (R1b) of the complex to form peroxy radicals, and hence the atmospheric significance of (R1) has yet to be rigorously verified by experiment.

Results from new quantum chemical calculations indicate that K1 is characterised by large uncertainties of at least an order of magnitude at T < 220 K. The large predicted values from Hermans et al. lie at the top end of the range of values obtained from calculations at different (higher) levels of theory. Atmospheric modelling studies demonstrated that whilst (R1) chemistry may be a significant loss process for CH3C(O)CH3 near the tropopause, it cannot explain observations of CH3C(O)OH throughout the troposphere.

Posted on 2 February 2012 | 12:00 am


Characterization of soluble bromide measurements and a case study of BrO observations during ARCTAS

Characterization of soluble bromide measurements and a case study of BrO observations during ARCTAS

Atmospheric Chemistry and Physics, 12, 1327-1338, 2012

Author(s): J. Liao, L. G. Huey, E. Scheuer, J. E. Dibb, R. E. Stickel, D. J. Tanner, J. A. Neuman, J. B. Nowak, S. Choi, Y. Wang, R. J. Salawitch, T. Canty, K. Chance, T. Kurosu, R. Suleiman, A. J. Weinheimer, R. E. Shetter, A. Fried, W. Brune, B. Anderson, X. Zhang, G. Chen, J. Crawford, A. Hecobian, and E. D. Ingall

A focus of the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission was examination of bromine photochemistry in the spring time high latitude troposphere based on aircraft and satellite measurements of bromine oxide (BrO) and related species. The NASA DC-8 aircraft utilized a chemical ionization mass spectrometer (CIMS) to measure BrO and a mist chamber (MC) to measure soluble bromide. We have determined that the MC detection efficiency to molecular bromine (Br2), hypobromous acid (HOBr), bromine oxide (BrO), and hydrogen bromide (HBr) as soluble bromide (Br?) was 0.9±0.1, 1.06+0.30/?0.35, 0.4±0.1, and 0.95±0.1, respectively. These efficiency factors were used to estimate soluble bromide levels along the DC-8 flight track of 17 April 2008 from photochemical calculations constrained to in situ BrO measured by CIMS. During this flight, the highest levels of soluble bromide and BrO were observed and atmospheric conditions were ideal for the space-borne observation of BrO. The good agreement (R2 = 0.76; slope = 0.95; intercept = ?3.4 pmol mol?1) between modeled and observed soluble bromide, when BrO was above detection limit (>2 pmol mol?1) under unpolluted conditions (NO<10 pmol mol?1), indicates that the CIMS BrO measurements were consistent with the MC soluble bromide and that a well characterized MC can be used to derive mixing ratios of some reactive bromine compounds. Tropospheric BrO vertical column densities (BrOVCD) derived from CIMS BrO observations compare well with BrOTROPVCD from OMI on 17 April 2008.

Posted on 2 February 2012 | 12:00 am





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