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.
Dissolved organic carbon (DOC) and select aldehydes in cloud and fog water: the role of the aqueous phase in impacting trace gas budgets
Atmospheric Chemistry and Physics, 13, 5117-5135, 2013
Author(s): B. Ervens, Y. Wang, J. Eagar, W. R. Leaitch, A. M. Macdonald, K. T. Valsaraj, and P. Herckes
Cloud and fog droplets efficiently scavenge and process water-soluble
compounds and, thus, modify the chemical composition of the gas and particle
phases. The concentrations of dissolved organic carbon (DOC) in the aqueous
phase reach concentrations on the order of ~ 10 mgC L?1
which is typically on the same order of magnitude as the sum of inorganic
anions. Aldehydes and carboxylic acids typically comprise a large fraction
of DOC because of their high solubility. The dissolution of species in the
aqueous phase can lead to (i) the removal of species from the gas phase
preventing their processing by gas phase reactions (e.g., photolysis of
aldehydes) and (ii) the formation of unique products that do not have any
efficient gas phase sources (e.g., dicarboxylic acids).
We present measurements of DOC and select aldehydes in fog water at high
elevation and intercepted clouds at a biogenically-impacted location
(Whistler, Canada) and in fog water in a more polluted area (Davis, CA).
Concentrations of formaldehyde, glyoxal and methylglyoxal were in the
micromolar range and comprised ≤ 2% each individually of the DOC.
Comparison of the DOC and aldehyde concentrations to those at other
locations shows good agreement and reveals highest levels for both in
anthropogenically impacted regions. Based on this overview, we conclude that
the fraction of organic carbon (dissolved and insoluble inclusions) in the
aqueous phase of clouds or fogs, respectively, comprises 2–~ 40%
of total organic carbon. Higher values are observed to be associated
with aged air masses where organics are expected to be more highly oxidised
and, thus, more soluble. Accordingly, the aqueous/gas partitioning ratio
expressed here as an effective Henry's law constant for DOC
(KH*DOC) increases by an order of magnitude from
7 × 103 M atm?1 to 7 × 104 M atm?1 during the
ageing of air masses.
The measurements are accompanied by photochemical box model simulations.
These simulations are used to contrast two scenarios, i.e., an
anthropogenically vs. a more biogenically impacted one as being
representative for Davis and Whistler, respectively. Since the simplicity of
the box model prevents a fully quantitative prediction of the observed
aldehyde concentrations, we rather use the model results to compare trends
in aldehyde partitioning and ratios. They suggest that the scavenging of
aldehydes by the aqueous phase can reduce HO2 gas phase levels
significantly by two orders of magnitude due to a weaker net source of
HO2 production from aldehyde photolysis in the gas phase. Despite the
high solubility of dicarbonyl compounds (glyoxal, methylglyoxal), their
impact on the HO2 budget by scavenging is < 10% of that of
formaldehyde. The overview of DOC and aldehyde measurements presented here
reveals that clouds and fogs can be efficient sinks for organics, with
increasing importance in aged air masses. Even though aldehydes,
specifically formaldehyde, only comprise ~ 1% of DOC, their
scavenging and processing in the aqueous phase might translate into
significant effects in the oxidation capacity of the atmosphere.
Evaluation of seasonal atmosphere–biosphere exchange estimations with TCCON measurements
Atmospheric Chemistry and Physics, 13, 5103-5115, 2013
Author(s): J. Messerschmidt, N. Parazoo, D. Wunch, N. M. Deutscher, C. Roehl, T. Warneke, and P. O. Wennberg
We evaluate three estimates of the atmosphere-biosphere exchange against
total column CO2 observations from the Total Carbon Column Observing
Network (TCCON). Using the GEOS-Chem transport model, we produce forward
simulations of atmospheric CO2 concentrations for the 2006–2010 time
period using the Carnegie-Ames-Stanford Approach (CASA), the Simple Biosphere
(SiB) and the GBiome-BGC models. Large differences in the CO2
simulations result from the choice of the atmosphere-biosphere model. We
evaluate the seasonal cycle phase, amplitude and shape of the simulations.
The version of CASA currently used as the a priori model by the GEOS-Chem
carbon cycle community poorly represents the season cycle in total column
CO2. Consistent with earlier studies, enhancing the CO2 uptake in
the boreal forest and shifting the onset of the growing season earlier
significantly improve the simulated seasonal CO2 cycle using CASA
estimates. The SiB model gives a better representation of the seasonal cycle
dynamics. The difference in the seasonality of net ecosystem exchange (NEE)
between these models is not the absolute gross primary productivity (GPP),
but rather the differential phasing of ecosystem respiration (RE) with
respect to GPP between these models.
Effects of internal mixing and aggregate morphology on optical properties of black carbon using a discrete dipole approximation model
Atmospheric Chemistry and Physics, 13, 5089-5101, 2013
Author(s): B. V. Scarnato, S. Vahidinia, D. T. Richard, and T. W. Kirchstetter
According to recent studies, internal mixing of black carbon (BC) with other
aerosol materials in the atmosphere alters its aggregate shape, absorption of
solar radiation, and radiative forcing. These mixing state effects are not
yet fully understood. In this study, we characterize the morphology and
mixing state of bare BC and BC internally mixed with sodium chloride (NaCl)
using electron microscopy and examine the sensitivity of optical properties
to BC mixing state and aggregate morphology using a discrete dipole
approximation model (DDSCAT). DDSCAT is flexible in simulating the geometry
and refractive index of particle aggregates. DDSCAT predicts a higher mass
absorption coefficient (MAC), lower single scattering albedo (SSA), and
higher absorption Angstrom exponent (AAE) for bare BC aggregates that are
lacy rather than compact. Predicted values of SSA at 550 nm range between
0.16 and 0.27 for lacy and compact aggregates, respectively, in agreement
with reported experimental values of 0.25 ± 0.05. The variation in
absorption with wavelength does not adhere precisely to a power law
relationship over the 200 to 1000 nm range. Consequently, AAE values depend
on the wavelength region over which they are computed. The MAC of BC
(averaged over the 200–1000 nm range) is amplified when internally mixed
with NaCl (100–300 nm in radius) by factors ranging from 1.0 for lacy BC
aggregates partially immersed in NaCl to 2.2 for compact BC aggregates fully
immersed in NaCl. The SSA of BC internally mixed with NaCl is higher than for
bare BC and increases with the embedding in the NaCl. Internally mixed BC SSA
values decrease in the 200–400 nm wavelength range, a feature also common
to the optical properties of dust and organics. Linear polarization features
are also predicted in DDSCAT and are dependent on particle size and
morphology.
This study shows that DDSCAT predicts complex morphology and mixing state
dependent aerosol optical properties that have been reported previously and
are relevant to radiative transfer, climate modeling, and interpretation of
remote sensing measurements.
Singular vector decomposition for sensitivity analyses of tropospheric chemical scenarios
Atmospheric Chemistry and Physics, 13, 5063-5087, 2013
Author(s): N. Goris and H. Elbern
Observations of the chemical state of the atmosphere typically provide only
sparse snapshots of the state of the system due to their insufficient
temporal and spatial density. One possibility for optimisation of the state
estimate is to target the observation of those parameters that have the
largest potential of resulting in forecast improvements. In the present work,
the technique of singular vector analysis is applied to atmospheric chemical
modelling in order to identify the most sensitive chemical compounds during a
given time period and prioritise them for measurement. Novel to the current
work is the fact that, in the application of singular vector analysis, not
only the initial values but also the emissions are considered as target
variables for adaptive observation strategies. This specific application of
singular vector analysis is studied in the context of a chemistry box model
allowing for validation of its new features for two chemical regimes. The
time and regime dependence of the ozone (O3) and peroxyacetyl nitrate
(PAN) formation potential of individual volatile organic compounds (VOCs) is
investigated. Results show that the combined sensitivity of O3 and PAN to
individual VOCs is strongly dependent on the photochemical scenario and
simulation interval used. Particularly the alkanes show increasing
sensitivities with increasing simulation length. Classifying the VOCs as being of
high, medium, little or negligible importance for the formation of
O3 and PAN allows for the identification of those VOCs that may be omitted
from measurement. We find that it is possible to omit 6 out of 18 VOCs
considered for initial value measurement and 4 out of 12 VOCs considered for
emission measurement. The omission of these VOCs is independent of
photochemical regime and simulation length. The VOCs selected for measuring
account for more than 96% and 90% of the O3 and PAN sensitivity to
VOCs, respectively.
Aerosol mixing state, hygroscopic growth and cloud activation efficiency during MIRAGE 2006
Atmospheric Chemistry and Physics, 13, 5049-5062, 2013
Author(s): S. Lance, T. Raatikainen, T. B. Onasch, D. R. Worsnop, X.-Y. Yu, M. L. Alexander, M. R. Stolzenburg, P. H. McMurry, J. N. Smith, and A. Nenes
Observations of aerosol hygroscopic growth and CCN activation spectra for
submicron particles are reported for the T1 ground site outside of Mexico
City during the MIRAGE 2006 campaign. ?-Köhler theory is used to
evaluate the characteristic hygroscopicity parameter, κ*, for the
CCN active aerosol population using both size-resolved HTMDA and
size-resolved CCNc measurements. Organic mass fractions
(forg) are evaluated from size-resolved aerosol mass
spectrometer (AMS) measurements, from which predictions of the hygroscopicity
parameter are compared against κ*.
Strong diurnal changes in aerosol water uptake parameters and aerosol
composition are observed. We find that new particle formation (NPF) events
are correlated with an increased κ* and CCN-active fraction during
the daytime, with greater impact on smaller particles. During NPF events, the
number concentration of 40 nm particles acting as CCN at 0.51% ± 0.06%
supersaturation can surpass by more than a factor of two the corresponding concentrations
of 100 nm particles. We also find that at
06:00–08:00 LT throughout the campaign, fresh traffic emissions
result in substantial changes to the chemical distribution of the aerosol,
with on average 65% externally mixed fraction for 40 nm particles and
30% externally mixed fraction for 100 nm particles, whereas at midday
nearly all particles of both sizes can be described as "internally mixed".
Average activation spectra and growth factor distributions are analyzed for
different time periods characterizing the daytime (with and without NPF
events), the early morning "rush hour" and the entire campaign. We show
that κ* derived from CCNc measurements decreases as a function of
size during all time periods, while the CCN-active fraction increases as a
function of size. Size-resolved AMS measurements do not predict the observed
trend for κ* versus particle size, which can be attributed to
unresolved mixing state and the presence of refractory material not measured
by the AMS. Measured κ* typically ranges from 0.2 to 0.35, and
organics typically make up 60–85 % of the aerosol mass in the size range
studied. We show that κAMS is able to
describe CCN concentrations reasonably well, provided mixing-state
information is available, especially at the highest CCN concentrations. This
is consistent with other CCN studies carried out in urban environments, and
is partly due to the fact that the highest CCN concentrations occur during
the daytime when the aerosol is internally mixed. During the early
morning rush hour, however, failing to account for the aerosol mixing state results
in systematic overestimation of CCN concentrations by as much as 50–100%
on average.
Stratospheric ozone interannual variability (1995–2011) as observed by lidar and satellite at Mauna Loa Observatory, HI and Table Mountain Facility, CA
Atmospheric Chemistry and Physics, 13, 5033-5047, 2013
Author(s): G. Kirgis, T. Leblanc, I. S. McDermid, and T. D. Walsh
The Jet Propulsion Laboratory (JPL) lidars, at the Mauna Loa Observatory,
Hawaii (MLO, 19.5° N, 155.6° W) and the JPL Table Mountain
Facility (TMF, California, 34.5° N, 117.7° W), have been
measuring vertical profiles of stratospheric ozone routinely since the early
1990's and late-1980s respectively. Interannual variability of ozone above
these two sites was investigated using a multi-linear regression analysis on
the deseasonalised monthly mean lidar and satellite time-series at 1 km
intervals between 20 and 45 km from January 1995 to April 2011, a period of
low volcanic aerosol loading. Explanatory variables representing the 11 yr
solar cycle, the El Niño Southern Oscillation, the Quasi-Biennial
Oscillation, the Eliassen-Palm flux, and horizontal and vertical transport
were used. A new proxy, the mid-latitude Ozone Depleting Gas Index, which
shows a decrease with time as an outcome of the Montreal Protocol, was
introduced and compared to the more commonly used linear trend method. The
analysis also compares the lidar time-series and a merged time-series
obtained from the space-borne Stratospheric Aerosol and Gas Experiment II,
Halogen Occultation Experiment, and Aura-Microwave Limb Sounder instruments.
The results from both lidar and satellite measurements are consistent with
recent model simulations which propose changes in tropical upwelling.
Additionally, at TMF the Ozone Depleting Gas Index explains as much variance
as the Quasi-Biennial Oscillation in the upper stratosphere. Over the past 17 yr a diminishing downward trend in ozone was observed before 2000 and a net
increase, and sign of ozone recovery, is observed after 2005. Our results
which include dynamical proxies suggest possible coupling between horizontal
transport and the 11 yr solar cycle response, although a dataset spanning a
period longer than one solar cycle is needed to confirm this result.
Modeling organic aerosol from the oxidation of ?-pinene in a Potential Aerosol Mass (PAM) chamber
Atmospheric Chemistry and Physics, 13, 5017-5031, 2013
Author(s): S. Chen, W. H. Brune, A. T. Lambe, P. Davidovits, and T. B. Onasch
A model has been developed to simulate the formation and evolution of
secondary organic aerosol (SOA) and was tested against data produced in a
Potential Aerosol Mass (PAM) flow reactor and a large environmental chamber.
The model framework is based on the two-dimensional volatility basis set
approach (2D-VBS), in which SOA oxidation products in the model are
distributed on the 2-D space of effective saturation concentration
(Ci*) and oxygen-to-carbon ratio (O : C). The modeled organic
aerosol mass concentrations (COA) and O : C agree with laboratory
measurements within estimated uncertainties. However, while both measured
and modeled O : C increase with increasing OH exposure as expected, the
increase of modeled O : C is rapid at low OH exposure and then slows as OH
exposure increases while the increase of measured O : C is initially slow and
then accelerates as OH exposure increases. A global sensitivity analysis
indicates that modeled COA values are most sensitive to the assumed
values for the number of Ci* bins, the heterogeneous OH
reaction rate coefficient, and the yield of first-generation products.
Modeled SOA O : C values are most sensitive to the assumed O : C of
first-generation oxidation products, the number of
Ci* bins, the heterogeneous OH reaction rate coefficient, and
the number of O : C bins. All these sensitivities vary as a function of OH
exposure. The sensitivity analysis indicates that the 2D-VBS model framework
may require modifications to resolve discrepancies between modeled and
measured O : C as a function of OH exposure.
Characterization of urban aerosol in Cork city (Ireland) using aerosol mass spectrometry
Atmospheric Chemistry and Physics, 13, 4997-5015, 2013
Author(s): M. Dall'Osto, J. Ovadnevaite, D. Ceburnis, D. Martin, R. M. Healy, I. P. O'Connor, I. Kourtchev, J. R. Sodeau, J. C. Wenger, and C. O'Dowd
Ambient wintertime background urban aerosol in Cork city, Ireland, was
characterized using aerosol mass spectrometry. During the three-week
measurement study in 2009, 93% of the ca. 1 350 000 single particles
characterized by an Aerosol Time-of-Flight Mass Spectrometer (TSI ATOFMS)
were classified into five organic-rich particle types, internally mixed to
different proportions with elemental carbon (EC), sulphate and nitrate,
while the remaining 7% was predominantly inorganic in nature.
Non-refractory PM1 aerosol was characterized using a High Resolution
Time-of-Flight Aerosol Mass Spectrometer (Aerodyne HR-ToF-AMS) and was also
found to comprise organic aerosol as the most abundant species (62%),
followed by nitrate (15%), sulphate (9%) and ammonium (9%), and
chloride (5%).
Positive matrix factorization (PMF) was applied to the HR-ToF-AMS organic
matrix, and a five-factor solution was found to describe the variance in the
data well. Specifically, "hydrocarbon-like" organic aerosol (HOA) comprised
20% of the mass, "low-volatility" oxygenated organic aerosol (LV-OOA)
comprised 18%, "biomass burning" organic aerosol (BBOA) comprised
23%, non-wood solid-fuel combustion "peat and coal" organic aerosol
(PCOA) comprised 21%, and finally a species type characterized by primary
\textit{m/z}~peaks at 41 and 55, similar to previously reported "cooking"
organic aerosol (COA), but possessing different diurnal variations to what
would be expected for cooking activities, contributed 18%.
Correlations between the different particle types obtained by the two
aerosol mass spectrometers are also discussed. Despite wood, coal and peat
being minor fuel types used for domestic space heating in urban areas, their
relatively low combustion efficiencies result in a significant contribution
to PM1 aerosol mass (44% and 28% of the total organic aerosol
mass and non-refractory total PM1, respectively).
Evaluating and constraining ice cloud parameterizations in CAM5 using aircraft measurements from the SPARTICUS campaign
Atmospheric Chemistry and Physics, 13, 4963-4982, 2013
Author(s): K. Zhang, X. Liu, M. Wang, J. M. Comstock, D. L. Mitchell, S. Mishra, and G. G. Mace
This study uses aircraft measurements of relative humidity and ice crystal
size distribution collected during the SPARTICUS (Small PARTicles In CirrUS)
field campaign to evaluate and constrain ice cloud parameterizations in the
Community Atmosphere Model version 5. About 200 h of data were collected
during the campaign between January and June 2010, providing the longest
aircraft measurements available so far for cirrus clouds in the
midlatitudes. The probability density function (PDF) of ice crystal number
concentration (Ni)
derived from the high-frequency (1 Hz)
measurements features a strong dependence on ambient temperature. As
temperature decreases from ?35 °C to ?62 °C, the peak
in the PDF shifts from 10–20 L?1 to 200–1000 L?1,
while Ni shows a factor of 6–7 increase.
Model simulations are performed with two different ice nucleation schemes for
pure ice-phase clouds. One of the schemes can reproduce a clear increase of
Ni with decreasing temperature by using either an
observation-based ice nuclei spectrum or a classical-theory-based spectrum with
a relatively low (5–10%) maximum freezing ratio for dust aerosols. The
simulation with the other scheme, which assumes a high maximum freezing ratio
(100%), shows much weaker temperature dependence of Ni.
Simulations are also performed to test empirical parameters related to water
vapor deposition and the autoconversion of ice crystals to snow. Results
show that a value between 0.05 and 0.1 for the water vapor deposition
coefficient, and 250 ?m for the critical diameter that
distinguishes ice crystals from snow, can produce good agreement between
model simulation and the SPARTICUS measurements in terms of Ni
and effective radius. The climate impact of perturbing
these parameters is also discussed.
Continuous atmospheric boundary layer observations in the coastal urban area of Barcelona during SAPUSS
Atmospheric Chemistry and Physics, 13, 4983-4996, 2013
Author(s): M. Pandolfi, G. Martucci, X. Querol, A. Alastuey, F. Wilsenack, S. Frey, C. D. O'Dowd, and M. Dall'Osto
Continuous measurements of surface mixed layer (SML), decoupled
residual/convective layer (DRCL) and aerosol backscatter coefficient were
performed within the Barcelona (Spain) boundary layer from September to
October 2010 (30 days) in the framework of the SAPUSS (Solving Aerosol
Problems by Using Synergistic Strategies) field campaign. Two near-infrared
ceilometers (Jenoptik CHM15K), vertically and horizontally probing (only
vertical profiles are herein discussed), were deployed. Ceilometer-based
DRCLs (1761 ± 363 m a.g.l.) averaged over the campaign duration were twice
as high as the mean SML (904 ± 273 m a.g.l.). Both DRCL and SML showed
a marked SML diurnal cycle. Ceilometer data were compared with potential
temperature profiles measured by daily radiosounding (twice a day, midnight
and midday) to interpret the boundary layer structure in the coastal urban
area of Barcelona. The overall agreement (R2 = 0.80) between the
ceilometer-retrieved and radiosounding-based SML heights (h) revealed
overestimation of the SML by the ceilometer (Δh=145 ± 145 m).
After separating the data in accordance with different atmospheric scenarios,
the lowest SML (736 ± 183 m) and DRCL (1573 ± 428 m) were
recorded during warm North African (NAF) advected air mass. By contrast,
higher SML and DRCL were observed during stagnant Regional (REG)
(911 ± 234 m and 1769 ± 314 m, respectively) and cold Atlantic
(ATL) (965 ± 222 m and 1878 ± 290 m, respectively) air masses.
In addition to being the lowest, the SML during the NAF scenario frequently
showed a flat upper boundary throughout the day possibly because of the
strong winds from the Mediterranean Sea limiting the midday SML convective
growth. The mean backscatter coefficients were calculated at two selected
heights representative of middle and top SML portions, i.e.
β500 = 0.59 ± 0.45 Mm?1 sr?1 and
β800 = 0.87 ± 0.68 Mm?1 sr?1 at 500 m and
800 m a.g.l., respectively. The highest backscatter coefficients were observed during NAF
(β500 = 0.77 ± 0.57 Mm?1 sr?1) when compared
with ATL (β500 = 0.51 ± 0.44 Mm?1 sr?1) and REG
(β500 = 0.64 ± 0.39 Mm?1 sr?1). The relationship
between the vertical change in backscatter coefficient and atmospheric
stability (∂θ/∂z) was investigated in the first
3000 m a.g.l., aiming to study how the unstable, stable or neutral
atmospheric conditions of the atmosphere alter the distribution of aerosol
backscatter with height over Barcelona. A positive correlation between
unstable conditions and enhanced backscatter and vice versa was found.
The mass and number size distributions of black carbon aerosol over Europe
Atmospheric Chemistry and Physics, 13, 4917-4939, 2013
Author(s): C. L. Reddington, G. McMeeking, G. W. Mann, H. Coe, M. G. Frontoso, D. Liu, M. Flynn, D. V. Spracklen, and K. S. Carslaw
Black carbon-containing aerosol particles play an important role in the
direct and indirect radiative forcing of climate. However, the magnitude and
sign of the net radiative effect is strongly dependent on the physical
properties of the black carbon (BC) component of the particles, such as mass
concentration, number size distribution and mixing state. Here we use a
global aerosol model combined with aircraft measurements of BC particle
number and size from the Single Particle Soot Photometer (SP2) to assess the
realism with which these physical properties are predicted by global models.
The comparison reveals a substantial mismatch between the measured and
modelled BC size distribution over the size range of the SP2 instrument
(90–400 nm BC diameter). The model predicts BC particle number
concentrations a factor ~3.5–5.7 higher than measured and a mode
diameter that is ~40–65 nm smaller than observed. More than
~90% of the model particles with dry diameters ≳260 nm
contain BC, while the observations suggest only 14% on average. These
model–observation biases in the BC properties are considerably greater than
for the overall particle distribution, suggesting that the discrepancy is
associated with model assumptions about the size and mixing state of the
emitted carbonaceous particles. We expect the discrepancy in BC size
distribution to be common among most global aerosol models, with implications
for model estimates of absorption optical depth and direct radiative forcing.
Effect of atmospheric organic complexation on iron-bearing dust solubility
Atmospheric Chemistry and Physics, 13, 4895-4905, 2013
Author(s): R. Paris and K. V. Desboeufs
Recent studies reported that the effect of organic complexation may be a
potentially important process to be considered by models estimating
atmospheric iron flux to the ocean. In this study, we investigated this
process effect by a series of dissolution experiments on iron-bearing dust in the
presence or the absence of various organic compounds (acetate, formate, oxalate, malonate, succinate,
glutarate, glycolate, lactate, tartrate and humic acid as an analogue of
humic like substances, HULIS) typically found in
atmospheric waters. Only 4 of tested organic ligands (oxalate,
malonate, tartrate and humic acid) caused an enhancement of iron solubility
which was associated with an increase of dissolved Fe(II) concentrations.
For all of these organic ligands, a positive linear dependence of iron
solubility to organic concentrations was observed and showed that the extent
of organic complexation on iron solubility decreased in the following order: oxalate
>malonate = tartrate > humic acid. This was
attributed to the ability of electron donors of organic ligands and implies
a reductive ligand-promoted dissolution. This study confirms that among the
known atmospheric organic binding ligands of Fe, oxalate is the most
effective ligand promoting dust iron solubility and showed, for the first
time, the potential effect of HULIS on iron dissolution under atmospheric
conditions.
Linkages between ozone-depleting substances, tropospheric oxidation and aerosols
Atmospheric Chemistry and Physics, 13, 4907-4916, 2013
Author(s): A. Voulgarakis, D. T. Shindell, and G. Faluvegi
Coupling between the stratosphere and the troposphere allows changes in
stratospheric ozone abundances to affect tropospheric chemistry. Large-scale
effects from such changes on chemically produced tropospheric aerosols have
not been systematically examined in past studies. We use a
composition-climate model to investigate potential past and future impacts
of changes in stratospheric ozone depleting substances (ODS) on tropospheric
oxidants and sulfate aerosols. In most experiments, we find significant
responses in tropospheric photolysis and oxidants, with small but
significant effects on methane radiative forcing. The response of sulfate
aerosols is sizeable when examining the effect of increasing future nitrous
oxide (N2O) emissions. We also find that without the regulation of
chlorofluorocarbons (CFCs) through the Montreal Protocol, sulfate aerosols
could have increased by 2050 by a comparable amount to the decreases
predicted due to relatively stringent sulfur emissions controls. The
individual historical radiative forcings of CFCs and N2O through their
indirect effects on methane (?22.6 mW m?2 for CFCs and ?6.7 mW m?2
for N2O) and sulfate aerosols (?3.0 mW m?2
for CFCs and +6.5 mW m?2 for N2O when considering the direct aerosol effect)
discussed here are non-negligible when compared to known historical ODS
forcing. Our results stress the importance of accounting for
stratosphere-troposphere, gas-aerosol and composition-climate interactions
when investigating the effects of changing emissions on atmospheric
composition and climate.
CO2 dispersion modelling over Paris region within the CO2-MEGAPARIS project
Atmospheric Chemistry and Physics, 13, 4941-4961, 2013
Author(s): C. Lac, R. P. Donnelly, V. Masson, S. Pal, S. Riette, S. Donier, S. Queguiner, G. Tanguy, L. Ammoura, and I. Xueref-Remy
Accurate simulation of the spatial and temporal variability of tracer mixing
ratios over urban areas is a challenging and interesting task needed to be
performed in order to utilise CO2 measurements in an atmospheric inverse
framework and to better estimate regional CO2 fluxes. This study
investigates the ability of a high-resolution model to simulate
meteorological and CO2 fields around Paris agglomeration during the March
field campaign of the CO2-MEGAPARIS project. The mesoscale atmospheric
model Meso-NH, running at 2 km horizontal resolution, is coupled with the
Town Energy Balance (TEB) urban canopy scheme and with the Interactions
between Soil, Biosphere and Atmosphere CO2-reactive (ISBA-A-gs) surface
scheme, allowing a full interaction of CO2 modelling between the surface
and the atmosphere. Statistical scores show a good representation of the
urban heat island (UHI) with stronger urban–rural contrasts on temperature
at night than during the day by up to 7 °C. Boundary layer heights
(BLH) have been evaluated on urban, suburban and rural sites during the
campaign, and also on a suburban site over 1 yr. The diurnal cycles of the
BLH are well captured, especially the onset time of the BLH increase and its
growth rate in the morning, which are essential for tall tower CO2
observatories. The main discrepancy is a small negative bias over urban and
suburban sites during nighttime (respectively 45 m and 5 m), leading to a
few overestimations of nocturnal CO2 mixing ratios at suburban sites and a
bias of +5 ppm. The diurnal CO2 cycle is generally well captured for all
the sites. At the Eiffel tower, the observed spikes of CO2 maxima occur
every morning exactly at the time at which the atmospheric boundary layer
(ABL) growth reaches the measurement height. At suburban ground stations,
CO2 measurements exhibit maxima at the beginning and at the end of each
night, when the ABL is fully contracted, with a strong spatio-temporal
variability. A sensitivity test without urban parameterisation removes the
UHI and underpredicts nighttime BLH over urban and suburban sites, leading to
large overestimation of nocturnal CO2 mixing ratio at the suburban sites
(bias of +17 ppm). The agreement between observation and prediction for BLH
and CO2 concentrations and urban–rural increments, both day and night,
demonstrates the potential of using the urban mesoscale system in the context
of inverse modelling
Overview of aerosol properties associated with air masses sampled by the ATR-42 during the EUCAARI campaign (2008)
Atmospheric Chemistry and Physics, 13, 4877-4893, 2013
Author(s): S. Crumeyrolle, A. Schwarzenboeck, J. C. Roger, K. Sellegri, J. F. Burkhart, A. Stohl, L. Gomes, B. Quennehen, G. Roberts, R. Weigel, P. Villani, J. M. Pichon, T. Bourrianne, and P. Laj
Within the frame of the European Aerosol Cloud Climate and Air Quality
Interactions (EUCAARI) project, the Météo-France aircraft ATR-42
performed 22 research flights over central Europe and the North Sea during
the intensive observation period in May 2008. For the campaign, the ATR-42
was equipped to study the aerosol physical, chemical, hygroscopic and
optical properties, as well as cloud microphysics. For the 22 research
flights, retroplume analyses along the flight tracks were performed with
FLEXPART in order to classify air masses into five sectors of origin,
allowing for a qualitative evaluation of emission influence on the
respective air parcel.
This study shows that the extensive aerosol parameters (aerosol mass and
number concentrations) show vertical decreasing gradients and in some air
masses maximum mass concentrations (mainly organics) in an intermediate
layer (1–3 km). The observed mass concentrations (in the boundary layer (BL): between 10 and
30 ?g m?3; lower free troposphere (LFT): 0.8 and 14 ?g m?3) are high especially
in comparison with the 2015 European norms for PM2.5 (25 ?g m?3)
and with previous airborne studies performed over England (Morgan et al.,
2009; McMeeking et al., 2012).
Particle number size distributions show a larger fraction of particles in
the accumulation size range in the LFT compared to BL. The chemical
composition of submicron aerosol particles is dominated by organics in the
BL, while ammonium sulphate dominates the submicron aerosols in the LFT,
especially in the aerosol particles originated from north-eastern Europe
(~ 80%), also experiencing nucleation events along the
transport. As a consequence, first the particle CCN acting ability, shown by
the CCN/CN ratio, and second the average values of the scattering
cross sections of optically active particles (i.e. scattering coefficient
divided by the optical active particle concentration) are increased in the
LFT compared to BL.
Insights into dissolved organic matter complexity in rainwater from continental and coastal storms by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry
Atmospheric Chemistry and Physics, 13, 4829-4838, 2013
Author(s): R. N. Mead, K. M. Mullaugh, G. Brooks Avery, R. J. Kieber, J. D. Willey, and D. C. Podgorski
A series of seven rainwater samples were collected in Wilmington, North
Carolina USA originating from both continental and coastal storms and
analyzed by ultrahigh resolution Fourier transform ion cyclotron resonance
mass spectrometry (FT-ICR MS). This data set is unique in that it represents
a detailed comparison of the molecular level composition of DOM in rainwater
collected from distinctly different air mass back trajectories by FT-ICR MS.
Approximately 25% of the roughly 2000 assigned CHO molecular formulas are
unique to a single storm classification indicating the importance of air mass
back trajectory on the composition of rainwater dissolved organic matter
(DOM). Analysis of the unique molecular formula assignments highlighted
distinct groupings of various bio- and geo-molecule classes with coastal
storms containing unique formulas representative of lignin and cellulose-like
formulas while continental storms had lipid-like formulas. A series of 18
distinct methylene oligomers were identified in coastal storms and 13 unique
methylene oligomers in continental storms, suggesting oligomer formation is
ubiquitous in rainwater albeit different for each storm classification.
Oligomers of small acids and C3H4O2 were detected in both
storm types indicating their processing may be similar in both back
trajectories. Condensed aromatic hydrocarbons were detected in continental
storms with phenol moieties that are not as oxidized as similar compounds
detected in aquatic DOM.
Evaluation of discrepancy between measured and modelled oxidized mercury species
Atmospheric Chemistry and Physics, 13, 4839-4863, 2013
Author(s): G. Kos, A. Ryzhkov, A. Dastoor, J. Narayan, A. Steffen, P. A. Ariya, and L. Zhang
L. Zhang et al. (2012), in a recent report, compared model estimates with new
observations of oxidized and particulate mercury species (Hg2+ and
Hgp) in the Great Lakes region and found that the sum of Hg2+ and
Hgp varied between a factor of 2 to 10 between measurements and model.
They suggested too high emission inputs as Hg2+ and too fast oxidative
conversion of Hg0 to Hg2+ and Hgp as possible causes. This
study quantitatively explores measurement uncertainties in detail. These
include sampling efficiency, composition of sample, interfering species and
calibration errors. Model (Global/Regional Atmospheric Heavy Metals Model –
GRAHM) sensitivity experiments are used to examine the consistency between
various Hg measurements and speciation of Hg near emission sources to better
understand the discrepancies between modelled and measured concentrations of
Hg2+ and Hgp. We find that the ratio of Hg0, Hg2+ and
Hgp in the emission inventories, measurements of surface air
concentrations of oxidized Hg and measurements of wet deposition are
currently inconsistent with each other in the vicinity of emission sources.
Current speciation of Hg emissions suggests higher concentrations of
Hg2+ in air and in precipitation near emission sources; however,
measured air concentrations of Hg2+ and measured concentrations of Hg
in precipitation are not found to be significantly elevated near emission
sources compared to the remote regions. The averaged unbiased root mean
square error (RMSE) between simulated and observed concentrations of
Hg2+ is found to be reduced by 42% and for Hgp reduced by
40% for 21 North American sites investigated, when a ratio for
Hg0 : Hg2+ : Hgp in the emissions is changed from 50 : 40 : 10
(as specified in the original inventories) to 90 : 8 : 2. Unbiased RMSE reductions
near emissions sources in the eastern United States and Canada are found to
be reduced by up to 58% for Hg2+. Significant improvement in the
model simulated spatial distribution of wet deposition of mercury in North
America is noticed with the modified Hg emission speciation.
Measurement-related uncertainties leading to lower estimation of Hg2+
concentrations are 86%. Uncertainties yielding either to higher or lower
Hg2+ concentrations are found to be 36%. Finally, anthropogenic
emission uncertainties are 106% for Hg2+. Thus it appears that the
identified uncertainties for model estimates related to mercury speciation
near sources, uncertainties in measurement methodology and uncertainties in
emissions can close the gap between modelled and observed estimates of
oxidized mercury found in L. Zhang et al. (2012). Model sensitivity simulations
show that the measured concentrations of oxidized mercury, in general, are
too low to be consistent with measured wet deposition fluxes in North
America. Better emission inventories (with respect to speciation), better
techniques for measurements of oxidized species and knowledge of mercury
reduction reactions in different environments (including in-plume) in all
phases are needed for improving the mercury models.
Evidence and quantitation of aromatic organosulfates in ambient aerosols in Lahore, Pakistan
Atmospheric Chemistry and Physics, 13, 4865-4875, 2013
Author(s): S. Kundu, T. A. Quraishi, G. Yu, C. Suarez, F. N. Keutsch, and E. A. Stone
Organosulfates are important components of atmospheric organic aerosols, yet
their structures, abundances, sources and formation processes are not
adequately understood. This study presents the identification and
quantitation of benzyl sulfate in atmospheric aerosols, which is the first
confirmed atmospheric organosulfate with aromatic carbon backbone. Benzyl
sulfate was identified and quantified in fine particulate matter (PM2.5)
collected in Lahore, Pakistan, during 2007–2008. An authentic standard of
benzyl sulfate was synthesized, standardized, and identified in atmospheric
aerosols with quadrupole time-of-flight (Q-ToF) mass spectrometry (MS).
Benzyl sulfate was quantified in aerosol samples using ultra performance
liquid chromatography (UPLC) coupled to negative electrospray ionization
triple quadrupole (TQ) MS. The highest benzyl sulfate concentrations were
recorded in November and January 2007 (0.50 ± 0.11 ng m?3)
whereas the lowest concentration was observed in July
(0.05 ± 0.02 ng m?3). To evaluate matrix effects, benzyl sulfate
concentrations were determined using external calibration and the method of
standard addition; comparable concentrations were detected by the two
methods, which ruled out significant matrix effects in benzyl sulfate
quantitation. Three additional organosulfates with m/z 187, 201 and
215 were qualitatively identified as aromatic organosulfates with additional
methyl substituents by high-resolution mass measurements and tandem MS. The
observed aromatic organosulfates form a homologous series analogous to
toluene, xylene, and trimethylbenzene, which are abundant anthropogenic
volatile organic compounds (VOC), suggesting that aromatic organosulfates may
be formed by secondary reactions. However, stronger statistical correlations
of benzyl sulfate with combustion tracers (EC and levoglucosan) than with
secondary tracers (SO42− and α-pinene-derived nitrooxy
organosulfates) suggest that aromatic organosulfates may be emitted from the
combustion sources or their subsequent atmospheric processing. Further
studies are needed to elucidate the sources and formation pathways of
aromatic organosulfates in the atmosphere.
Continuous monitoring of summer surface water vapor isotopic composition above the Greenland Ice Sheet
Atmospheric Chemistry and Physics, 13, 4815-4828, 2013
Author(s): H. C. Steen-Larsen, S. J. Johnsen, V. Masson-Delmotte, B. Stenni, C. Risi, H. Sodemann, D. Balslev-Clausen, T. Blunier, D. Dahl-Jensen, M. D. Ellehøj, S. Falourd, A. Grindsted, V. Gkinis, J. Jouzel, T. Popp, S. Sheldon, S. B. Simonsen, J. Sjolte, J. P. Steffensen, P. Sperlich, A. E. Sveinbjörnsdóttir, B. M. Vinther, and J. W. C. White
We present here surface water vapor isotopic measurements conducted from
June to August 2010 at the NEEM (North Greenland Eemian Drilling
Project) camp, NW Greenland (77.45° N,
51.05° W, 2484 m a.s.l.). Measurements were conducted at 9
different heights from 0.1 m to 13.5 m above the snow surface using
two different types of cavity-enhanced near-infrared absorption spectroscopy
analyzers. For each instrument specific protocols were developed for
calibration and drift corrections. The inter-comparison of corrected results
from different instruments reveals excellent reproducibility, stability, and
precision with a standard deviations of ~ 0.23‰ for δ18O and ~ 1.4‰ for ?D. Diurnal and intraseasonal variations
show strong relationships between changes in local surface humidity and
water vapor isotopic composition, and with local and synoptic weather
conditions. This variability probably results from the interplay between
local moisture fluxes, linked with firn–air exchanges, boundary layer
dynamics, and large-scale moisture advection. Particularly remarkable are
several episodes characterized by high (> 40‰) surface water vapor deuterium excess. Air mass
back-trajectory calculations from atmospheric analyses and water tagging in
the LMDZiso (Laboratory of Meteorology Dynamics Zoom-isotopic) atmospheric model reveal that these events are associated with
predominant Arctic air mass origin. The analysis suggests that high
deuterium excess levels are a result of strong kinetic fractionation during
evaporation at the sea-ice margin.
Aerosol size-resolved trace metal composition in remote northern tropical Atlantic marine environment: case study Cape Verde islands
Atmospheric Chemistry and Physics, 13, 4801-4814, 2013
Author(s): K. W. Fomba, K. Müller, D. van Pinxteren, and H. Herrmann
Size-resolved trace metal concentrations of 15 elements in aerosol particles
at the Cape Verde Atmospheric Observatory (CVAO) under remote background
conditions were investigated through analysis of aerosol samples collected
during intensive field studies from January 2007 to November 2011 using
total reflection x-ray fluorescence (TXRF). The identification of the main
air mass origin that influence remote marine aerosol in the northern
tropical Atlantic has been investigated. In total, 317 samples were
collected. The dataset was analyzed according to the main air mass inflow at
the station. We found that remote conditions make up about 45% of the
meteorological conditions in a year at CVAO and thus the northern tropical
Atlantic. Surprisingly, air masses from North America are often responsible
for higher trace metal concentrations in this region.
Elements such as Zn, Pb, Cu, Cr, Ni, and V were mostly found in the
submicron size fractions, while elements with dominant crustal or oceanic
origin such as Fe, Ti, Mn, Sr, and Rb were found in the coarse fractions
(>1 ?m). The highest metal concentrations, especially for
Zn (3.23 ng m?3), Cu (0.81 ng m?3), Sr
(2.63 ng m?3), and Cr (0.53 ng m?3), were
observed in air masses originating from North America and the concentrations
were within the same concentration range to those reported previously in the
literature for remote marine aerosols. Fe (12.26 ng m?3),
Ti (0.91 ng m?3), and Mn (0.35 ng m?3)
showed higher concentrations when air mass came from Europe and the Canary
Islands. Pb concentration was low (<0.20 ng m?3)
and did not vary significantly with air mass direction. The low Pb
concentration is indicative of the complete phase-out of leaded gasoline
even in African countries. Crustal enrichment factor values decreased from
fine to coarse-mode particles with low values (<4) observed for Fe,
Mn, and Rb, and high values (>20) for Zn, Cu, Ni, Cr, Pb, and Se.
The observed enrichment of the elements was attributed to crustal, marine,
anthropogenic, and biogenic sources, as well as long-range transport and
resuspension. Zn, Cu and Pb were indicators of anthropogenic activities,
while Ti and Sr were indicators of crustal and marine origin,
respectively. Oceanic and biogenic emissions might have contributed to most
of the Se observed. This work provides the first long-term size-resolved
trace metals study for remote tropical northern Atlantic marine aerosols and
the dataset could serve as good initiation of yearly flux estimates.
Posted on 8 May 2013 | 12:00 am
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