Atmospheric Chemistry and Physics - Current Research Articles
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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
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.
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.
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.
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.
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.
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.
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.
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).
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.
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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