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ABSTRACT: 1] As part of the Indian Ocean Experiment (INDOEX) 1999 Intensive Field Phase, measurements of aerosol properties were made on board the R/V Ronald H. Brown in the Indian Ocean north and south of the Intertropical Convergence Zone (ITCZ) in the Arabian Sea and in the Bay of Bengal. On the basis of air mass trajectories, eight air mass source regions were identified including the southern hemisphere Atlantic; southern hemisphere Indian Ocean; northern hemisphere Indian Ocean; east Indian subcontinent where trajectories came from near Calcutta, through the southern portion of India, and then to the ship; Indian subcontinent where trajectories came from across central India to the ship; Arabia; Arabia/Indian subcontinent, a mixed region where lower-level trajectories came from Arabia and upper-level trajectories came from India; and Arabian Sea/coastal India where trajectories came from along the coast of India to the ship. Properties of the aerosol measured in the marine boundary layer included chemical composition, number size distribution, and scattering and absorption coefficients. In addition, vertical profiles of aerosol backscatter and optical depth were measured. Presented here as a function of air mass source region are the concentrations and mass fractions of the dominant aerosol chemical components, the fraction of the extinction measured at the surface due to each component, mass extinction efficiencies of the individual components, aerosol scattering and absorption coefficients, single scattering albedo, Å ngström exponent, and optical depth. All results except aerosol optical depth are reported at the measurement relative humidity of 55 5%. For air masses that originated from the two southern hemisphere marine regions (southern hemisphere Atlantic and Indian Ocean), sea salt dominated the extinction by sub-1 m and sub-10 m aerosol particles. The ratios of sub-1m to sub-10 m extinction were the lowest measured of all air mass source regions (mean values of 28 and 40%) due to the dominance of the aerosol mass by supermicron sea salt. In addition, aerosol optical depths were the lowest measured averaging 0.06 0.03. Non-sea-salt (nss) sulfate aerosol concentrations in air masses from the northern hemisphere Indian Ocean were a factor of 6 higher than those in southern hemisphere air masses, while submicron sea-salt concentrations were comparable. Sulfate aerosol made up 40% of the sub-1m extinction, while sea salt dominated the sub-10 m extinction. Aerosol optical depths for this source region averaged 0.10 0.03. A mean single scattering albedo near 0.89 and detectable black carbon (BC) concentrations (0.14 0.05 g m 3) indicated the transport of continentally derived aerosol to the ITCZ. The two regions influenced by low-level (500 m) airflow from Arabia had higher concentrations of submicron nss sulfate, particulate organic matter (POM), and inorganic oxidized material (IOM) than were observed in the marine regions. Concentrations of supermicron IOM were comparable to supermicron sea-salt concentrations. Nss sulfate aerosol dominated the sub-1 m extinction and made significant contributions to the sub-10 m extinction. Sea salt dominated the supermicron extinction. Mean BC contributions to submicron extinction were 8 and 12%. Single scattering albedo values averaged 0.93 0.02 and 0.89 0.02 for these two source regions. Aerosol optical depths averaged 0.19 0.12 and 0.38 0.07 with the higher value due to upper-level (2500 m) flow from India. Regions influenced by low-level airflow from the Indian subcontinent had the highest submicron nss sulfate, POM, BC, and IOM concentrations measured during the experiment. Supermicron sea-salt concentrations were lower than or comparable to supermicron nitrate concentrations. Sub-1 m and sub-10 INX2 19 -1 m extinction were dominated by nss sulfate aerosol although a burning component consisting of BC, KNO 3 , and K 2 SO 4 made a nearly equivalent contribution. These regions had a mean single scattering albedo of 0.85 0.01, the lowest measured for any region. Mean aerosol optical depths were highest (0.3 to 0.4) for regions with low-level or upper-level airflow from the Indian subcontinent.
J. Geophys. Res. ; 107(8020).
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C.D. Cappa,
E. Williams,
G. Buffaloe,
B. Lerner,
T.B. Onasch,
D.A. Lack,
I. Naunaan,
S-M. Li,
K. Hayden,
P. Massoli, P. K. Quinn,
T. S. Bates
In Preparation. 01/2012;
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A. Smirnov,
A. M. Sayer,
B. N. Holben,
N. C. Hsu,
S. M. Sakerin,
A. Macke,
N. B. Nelson,
Y. Courcoux,
T. J. Smyth,
P. Croot, P. K. Quinn,
J. Sciare,
S. K. Gulev,
S. Piketh,
R. Losno,
S. Kinne,
V. F. Radionov
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ABSTRACT: The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. The MAN archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we investigate correlations between ship-borne aerosol optical depth (AOD) and near-surface wind speed, either measured (on-board or from satellite) or modeled (NCEP). According to our analysis, wind speed influences columnar aerosol optical depth, although the slope of the linear regression between AOD and wind speed is not steep (similar to 0.004-0.005), even for strong winds over 10m s(-1). The relationships show significant scatter (correlation coefficients typically in the range 0.3-0.5); the majority of this scatter can be explained by the uncertainty on the input data. The various wind speed sources considered yield similar patterns. Results are in good agreement with the majority of previously published relationships between surface wind speed and ship-based or satellite-based AOD measurements. The basic relationships are similar for all the wind speed sources considered; however, the gradient of the relationship varies by around a factor of two depending on the wind data used.
Atmospheric Measurement Techniques 01/2012; 5(2):377-388. · 3.34 Impact Factor
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T S Bates, P K Quinn,
A A Frossard,
L M Russell,
J Hakala,
T Petäjä,
M Kulmala,
D S Covert,
C D Cappa,
S -M Li,
K L Hayden,
I Nuaaman,
R McLaren,
P Massoli,
M R Canagaratna,
T B Onasch,
D Sueper,
D R Worsnop,
W C Keene
Journal of Geophysical Research: Atmospheres. 01/2012; 117(D21):n/a-n/a.
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ABSTRACT: More than twenty years ago, a biological regulation of climate was proposed whereby emissions of dimethyl sulphide from oceanic phytoplankton resulted in the formation of aerosol particles that acted as cloud condensation nuclei in the marine boundary layer. In this hypothesis--referred to as CLAW--the increase in cloud condensation nuclei led to an increase in cloud albedo with the resulting changes in temperature and radiation initiating a climate feedback altering dimethyl sulphide emissions from phytoplankton. Over the past two decades, observations in the marine boundary layer, laboratory studies and modelling efforts have been conducted seeking evidence for the CLAW hypothesis. The results indicate that a dimethyl sulphide biological control over cloud condensation nuclei probably does not exist and that sources of these nuclei to the marine boundary layer and the response of clouds to changes in aerosol are much more complex than was recognized twenty years ago. These results indicate that it is time to retire the CLAW hypothesis.
Nature 12/2011; 480(7375):51-6. · 36.28 Impact Factor
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Yang M,
B. J. Huebert,
B. W. Blomquist,
S. G. Howell,
L. M. Shank,
C. S. McNaughton,
A. D. Clarke,
L. N. Hawkins,
L. M. Russell,
D S Covert, [......],
T. S. Bates, P. K. Quinn,
Zagorac N,
A. R. Bandy,
S. P. de Szoeke,
P. D. Zuidema,
S. C. Tucker,
W. A. Brewer,
K. B. Benedict,
J. L. Collett
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ABSTRACT: Dimethylsulfide (DMS) emitted from the ocean is a biogenic precursor gas for sulfur dioxide (SO2) and non-sea-salt sulfate aerosols (SO42). During the VAMOS-Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in 2008, multiple instrumented platforms were deployed in the Southeastern Pacific (SEP) off the coast of Chile and Peru to study the linkage between aerosols and stratocumulus clouds. We present here observations from the NOAA Ship Ronald H. Brown and the NSF/NCAR C-130 aircraft along ~20° S from the coast (70° W) to a remote marine region (85° W). While SO42− and SO2 concentrations were distinctly elevated above background levels in the coastal marine boundary layer (MBL) due to anthropogenic influence (~800 and 80 pptv, respectively), their concentrations rapidly decreased offshore (~100and 25 pptv). Compared to the "mass" entrainment fluxes of SO42− and SO2 from the free troposphere (0.5 ± 0.3 and 0.3 ± 0.2 μmoles m−2 day−1), the sea-to-air DMS flux (3.8 ± 0.1 μmoles m−2 day−1) remained the predominant source of sulfur mass to the MBL. In-cloud oxidation was found to be the most important mechanism for SO2 removal and in situ SO42− production. Surface SO42− loading in the remote region displayed pronounced diel variability, increasing rapidly in the first few hours after sunset and then decaying for the rest of the time. We theorize that the increase in SO42− was due to nighttime recoupling of the MBL that mixed down cloud-processed air, while decoupling and sporadic precipitation scavenging were responsible for the daytime decline in SO42−.
Atmospheric Chemistry and Physics Discussions. 01/2011;
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Smirnov A,
B. N. Holben,
D. M. Giles,
Slutsker I,
N. T. O&apos,
Neill,
T. F. Eck,
Macke A,
Croot P,
Courcoux Y, [......],
J. S. Reid,
Schulz M,
C. L. Heald,
Zhang J,
Lapina K,
R. G. Kleidman,
Griesfeller J,
B. J. Gaitley,
Tan Q,
T. L. Diehl
[show abstract]
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ABSTRACT: The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. Over 80 cruises were completed through early 2010 with deployments continuing. Measurements areas included various parts of the Atlantic Ocean, the Northern and Southern Pacific Ocean, the South Indian Ocean, the Southern Ocean, the Arctic Ocean and inland seas. MAN deploys Microtops hand-held sunphotometers and utilizes a calibration procedure and data processing traceable to AERONET. Data collection included areas that previously had no aerosol optical depth (AOD) coverage at all, particularly vast areas of the Southern Ocean. The MAN data archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we present results of AOD measurements over the oceans, and make a comparison with satellite AOD retrievals and model simulations.
Atmospheric Measurement Techniques 01/2011; 4(3):583-597. · 3.34 Impact Factor
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C A Brock,
J Cozic,
R Bahreini,
K D Froyd,
A M Middlebrook,
A McComiskey,
J Brioude,
O R Cooper,
A Stohl,
K C Aikin, [......],
J P Schwarz,
H Sodemann,
J R Spackman,
H Stark,
D S Thomson,
T Thornberry,
P Veres,
L A Watts,
C Warneke,
A G Wollny
Atmospheric Chemistry and Physics. 01/2011; 11(6):2423-2453.
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C. A. Brock,
J. Cozic,
R. Bahreini,
K. D. Froyd,
A. M. Middlebrook,
A. McComiskey,
J. Brioude,
O. R. Cooper,
A. Stohl,
K. C. Aikin, [......],
J. P. Schwarz,
H. Sodemann,
J. R. Spackman,
H. Stark,
D. S. Thomson,
T. Thornberry,
P. Veres,
L. A. Watts,
C. Warneke,
A. G. Wollny
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ABSTRACT: We present an overview of the background, scientific goals, and
execution of the Aerosol, Radiation, and Cloud Processes affecting
Arctic Climate (ARCPAC) project of April 2008. We then summarize
airborne measurements, made in the troposphere of the Alaskan Arctic, of
aerosol particle size distributions, composition, and optical properties
and discuss the sources and transport of the aerosols. The aerosol data
were grouped into four categories based on gas-phase composition. First,
the background troposphere contained a relatively diffuse, sulfate-rich
aerosol extending from the top of the sea-ice inversion layer to 7.4 km
altitude. Second, a region of depleted (relative to the background)
aerosol was present within the surface inversion layer over sea-ice.
Third, layers of dense, organic-rich smoke from open biomass fires in
Southern Russia and Southeastern Siberia were frequently encountered at
all altitudes from the top of the inversion layer to 7.1 km. Finally,
some aerosol layers were dominated by components originating from fossil
fuel combustion. Of these four categories measured during ARCPAC,
the diffuse background aerosol was most similar to the average
springtime aerosol properties observed at a long-term monitoring site at
Barrow, Alaska. The biomass burning (BB) and fossil fuel layers were
present above the sea-ice inversion layer and did not reach the sea-ice
surface during the course of the ARCPAC measurements. The BB aerosol
layers were highly scattering and were moderately hygroscopic. On
average, the layers produced a noontime net heating of ~0.1 K
day-1 between 2 and 7 km and a~slight cooling at the
surface. The ratios of particle mass to carbon monoxide (CO) in the BB
plumes, which had been transported over distances >5000 km, were
comparable to the high end of literature values derived from previous
measurements in fresh wildfire smoke. These ratios suggest minimal
precipitation scavenging and removal of the BB particles between the
time they were emitted and the time they were observed in dense layers
above the sea-ice inversion layer.
Atmospheric Chemistry and Physics 10/2010; 10:27361-27434. · 4.88 Impact Factor
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Proceedings of the National Academy of Sciences 03/2010; 107:6652-6657. · 9.68 Impact Factor
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ABSTRACT: 1] Submicron particles were collected on board the NOAA R/V Ronald H. Brown during the VAMOS Ocean‐Cloud‐Atmosphere‐Land Study Regional Experiment (VOCALS‐REx) in the southeast Pacific marine boundary layer in October and November 2008. The aerosol in this region was characterized by low numbers of particles (150–700 cm −3) that were dominated by sulfate ions at concentrations of 0.9 ± 0.7 mg m −3 and organic mass at 0.6 ± 0.4 mg m −3 , with no measurable nitrate and low ammonium ion concentrations. Measurements of submicron organic aerosol functional groups and trace elements show that continental outflow of anthropogenic emissions is the dominant source of organic mass (OM) to the southeast Pacific with an additional, smaller contribution of organic mass from primary marine sources. This continental source is supported by a correlation between OM and radon. Saturated aliphatic C‐CH (alkane) composed 41 ± 27% of OM. Carboxylic acid COOH (32 ± 23% of OM) was observed in single particles internally mixed with ketonic carbonyl, carbonate, and potassium. Organosulfate COSO 3 (4 ± 8% of OM) was observed only during the periods of highest organic and sulfate concentrations and lowest ammonium concentrations, consistent with a sulfuric acid epoxide hydrolysis for proposed surrogate compounds (e.g., isoprene oxidation products) or reactive glyoxal uptake mechanisms from laboratory studies. This correlation suggests that in high‐sulfate, low‐ammonium conditions, the formation of organosulfate compounds in the atmosphere contributes a significant fraction of aerosol OM (up to 13% in continental air masses). Organic hydroxyl C‐OH composed 20 ± 12% of OM and up to 50% of remote marine OM and was inversely correlated with radon indicating a marine source. A two‐factor solution of positive matrix factorization (PMF) analysis resulted in one factor dominated by organic hydroxyl (>70% by mass) and one factor dominated by saturated aliphatic C‐CH (alkane) and carboxylic acid (together, 90% by mass), identified as the marine and combustion factors, respectively. Measurements of particle concentrations in the study region compared with concentrations estimated from MODIS aerosol optical depth indicate that continental outflow results in MBL particle concentrations elevated up to 2 times the background level (less than 300 cm −3) away from shore and up to 10 times the background level at the coast. The presence of both coastal fossil fuel combustion and marine sources of oxygenated organic aerosol results in little change in the oxygenated fraction and oxygen to carbon ratio (O/C) along the outflow of the region's dominant organic particle source.
J. Geophys. Res. 01/2010; 115.
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H. Simon,
Y. Kimura,
G. McGaughey,
D.T. Allen,
S.S. Brown,
D. Coffman,
J.E. Dibb,
H.D. Osthoff, P.K. Quinn,
J. M. Roberts,
G. Yarwood,
D. Kemball-Cook,
D. Byun,
D. Lee
Atmos. Environ. 01/2010; 44:5476-5488.
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ABSTRACT: During the 2006 Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS-GoMACCS 2006), the optical, chemical and microphysical properties of atmospheric aerosols were measured on multiple mobile platforms and at ground based stations. In situ measurements of the aerosol light extinction coefficient (σep) were performed by two multi-wavelength cavity ring-down (CRD) instruments, one located on board the NOAA R/V Ronald H. Brown (RHB) and the other located at the University of Houston, Moody Tower (UHMT). An AERONET sunphotometer was also located at the UHMT to measure the columnar aerosol optical depth (AOD). The σep data were used to extract the extinction Ångström exponent (åep), a measure of the wavelength dependence of σep. There was general agreement between the åep (and to a lesser degree σep) measurements by the two spatially separated CRD instruments during multi-day periods, suggesting a regional scale consistency of the sampled aerosols. Two spectral models are applied to the σep and AOD data to extract the fine mode fraction of extinction (η) and the fine mode effective radius (Reff,f). These two parameters are robust measures of the fine mode contribution to total extinction and the fine mode size distribution, respectively. The results of the analysis are compared to Reff,f values extracted using AERONET V2 retrievals and calculated from in situ particle size measurements on the RHB and at UHMT. During a time period when fine mode aerosols dominated the extinction over a large area extending from Houston/Galveston Bay and out into the Gulf of Mexico, the various methods for obtaining Reff,f agree qualitatively (showing the same temporal trend) and quantitatively (pooled standard deviation = 28 nm).
Atmospheric Chemistry and Physics. 01/2010;
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ABSTRACT: As a part of the IPY project POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate Chemistry, Aerosols and Transport), this paper studies the sources of equivalent black carbon (EBC), sulphate, light-scattering aerosols and ozone measured at the Arctic stations Zeppelin, Alert, Barrow and Summit during the years 2000–2007. These species are important pollutants and climate forcing agents, and sulphate and EBC are main components of Arctic haze. To determine where these substances originate, the measurement data were combined with calculations using FLEXPART, a Lagrangian particle dispersion model. The climatology of atmospheric transport from surrounding regions on a twenty-day time scale modelled by FLEXPART shows that the stations Zeppelin, Alert and Barrow are highly sensitive to surface emissions in the Arctic and to emissions in high-latitude Eurasia in winter. Emission sensitivities over southern Asia and southern North America are small throughout the year. The high-altitude station Summit is an order of magnitude less sensitive to surface emissions in the Arctic whereas emissions in the southern parts of the Northern Hemisphere continents are more influential relative to the other stations. Our results show that for EBC and sulphate measured at Zeppelin, Alert and Barrow, northern Eurasia is the dominant source region. For sulphate, Eastern Europe and the metal smelting industry in Norilsk are particularly important. For EBC, boreal forest fires also contribute in summer. No evidence for any substantial contribution to EBC from sources in southern Asia is found. European air masses are associated with low ozone concentrations in winter due to titration by nitric oxides, but are associated with high ozone concentrations in summer due to photochemical ozone formation. There is also a strong influence of ozone depletion events in the Arctic boundary layer on measured ozone concentrations in spring and summer. These results will be useful for developing emission reduction strategies for the Arctic.
Atmospheric Chemistry and Physics. 01/2010;
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ABSTRACT: As a part of the IPY project POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols and Transport) and building on previous work (Hirdman et al., 2010), this paper studies the long-term trends of both atmospheric transport as well as equivalent black carbon (EBC) and sulphate for the three Arctic stations Alert, Barrow and Zeppelin. We find a general downward trend in the measured EBC concentrations at all three stations, with a decrease of −2.1±0.4 ng m−3 yr−1 (for the years 1989–2008) and −1.4±0.8 ng m−3 yr−1 (2002–2009) at Alert and Zeppelin respectively. The decrease at Barrow is, however, not statistically significant. The measured sulphate concentrations show a decreasing trend at Alert and Zeppelin of −15±3 ng m−3 yr−1 (1985–2006) and −1.3±1.2 ng m−3 yr−1 (1990–2008) respectively, while the trend at Barrow is unclear. To reveal the influence of different source regions on these trends, we used a cluster analysis of the output of the Lagrangian particle dispersion model FLEXPART run backward in time from the measurement stations. We have investigated to what extent variations in the atmospheric circulation, expressed as variations in the frequencies of the transport from four source regions with different emission rates, can explain the long-term trends in EBC and sulphate measured at these stations. We find that the long-term trend in the atmospheric circulation can only explain a minor fraction of the overall downward trend seen in the measurements of EBC (0.3–7.2%) and sulphate (0.3–5.3%) at the Arctic stations. The changes in emissions are dominant in explaining the trends. We find that the highest EBC and sulphate concentrations are associated with transport from Northern Eurasia and decreasing emissions in this region drive the downward trends. Northern Eurasia (cluster: NE, WNE and ENE) is the dominant emission source at all Arctic stations for both EBC and sulphate during most seasons. In wintertime, there are indications that the EBC emissions from the eastern parts of Northern Eurasia (ENE cluster) have increased over the last decade.
Atmospheric Chemistry and Physics Discussions. 01/2010;
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ABSTRACT: Aerosol measurements at Barrow, Alaska during the past 30 years have identified the long range transport of pollution associated with Arctic Haze as well as ocean-derived aerosols of more local origin. Here, we focus on measurements of aerosol chemical composition to assess (1) trends in Arctic Haze aerosol and implications for source regions, (2) the interaction between pollution-derived and ocean-derived aerosols and the resulting impacts on the chemistry of the Arctic boundary layer, and (3) the response of aerosols to a changing climate. Aerosol chemical composition measured at Barrow, AK during the Arctic haze season is compared for the years 1976–1977 and 1997–2008. Based on these two data sets, concentrations of non-sea salt (nss) sulfate (SO4=) and non-crustal (nc) vanadium (V) have decreased by about 60% over this 30 year period. Consistency in the ratios of nss SO4=/ncV and nc manganese (Mn)/ncV between the two data sets indicates that, although emissions have decreased in the source regions, the source regions have remained the same over this time period. The measurements from 1997–2008 indicate that, during the haze season, the nss SO4= aerosol at Barrow is becoming less neutralized by ammonium (NH4+) yielding an increasing sea salt aerosol chloride (Cl−) deficit. The expected consequence is an increase in the release of Cl atoms to the atmosphere and a change in the lifetime of volatile organic compounds (VOCs) including methane. In addition, summertime concentrations of biogenically-derived methanesulfonate (MSA−) and nss SO4= are increasing at a rate of 12 and 8% per year, respectively. Further research is required to assess the environmental factors behind the increasing concentrations of biogenic aerosol.
Atmospheric Chemistry and Physics. 01/2009;
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Aerosol Science and Technology. 01/2009; 43:486-501.
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Geophysical Research Letters 01/2009; 36(L14813):doi:10.1029/2009GL038979. · 3.79 Impact Factor
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Journal of Geophysical Research 01/2009; 114(D00F07):doi:10.1029/2008JD011604. · 3.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Aerosol measurements at Barrow, AK during the past 30 years have identified the long range transport of pollution associated with Arctic Haze as well as ocean-derived aerosols of more local origin. Here, we focus on measurements of aerosol chemical composition to assess 1) trends in Arctic Haze aerosol and implications for source regions, 2) the interaction between pollution-derived and ocean-derived aerosols and the resulting impacts on the chemistry of the Arctic boundary layer, and 3) the response of aerosols to a changing climate. Aerosol chemical composition measured at Barrow, AK during the Arctic haze season is compared for the years 1976–1977 and 1997–2008. Based on these two data sets, concentrations of non-sea salt (nss) sulfate (SO4=) and non-crustal (nc) vanadium (V) have decreased by about 60% over this 30 year period. Consistency in the ratios of nss SO4=/ncV and nc manganese (Mn)/ncV between the two data sets indicates that, although emissions have decreased in the source regions, the source regions have remained the same over this time period. The measurements from 1997–2008 indicate that, during the haze season, the nss SO4= aerosol at Barrow is becoming less neutralized by ammonium (NH4+) yielding an increasing sea salt aerosol chloride (Cl−) deficit. The expected consequence is an increase in the release of Cl atoms to the atmosphere and a change in the lifetime of volatile organic compounds (VOCs) including methane. In addition, summertime concentrations of biogenically-derived methanesulfonate (MSA−) and nss SO4= are increasing at a rate of 12 and 8% per year, respectively. Further research is required to assess the environmental factors behind the increasing concentrations of biogenic aerosol.
Atmospheric Chemistry and Physics Discussions. 01/2009;
