Nss SO42 Research Articles

Hydrochemistry of atmospheric precipitation over an urban station in the peninsular India: Assessment of the long-term data

Long-term data on precipitation chemistry is crucial for the formulation of climatology of major acidifying as well as neutralizing components and their trends over the years. Rain water samples were collected during the monsoon season (June to September) for three decades (1981–2016) at Pune, an urban global atmospheric watch (GAW) station in the peninsular India. The long-term volume weighted mean (VWM) pH was 5.91 ± 0.57. The pH showed a significantly decreasing trend with about 9% acidic occurrences. Temporal variation of annual mean nss SO42- and NO3-showed an increasing trend whereas, a decreasing trend of NH4+and an increasing trend of Ca 2+was observed. The lowest mean wet deposition flux during the monsoon season over the entire period was observed for NH4+and highest was for NO3-. Source apportionment for ionic components through Positive Matrix Factorization (PMF) indicated the factor comprising of crustal source contributed 35% to the total ionic concentration followed by the sea salt ions that comprised of 33%. The anthropogenic sources mainly comprising of industrial, vehicular, agricultural and residential activities also contributed significantly (25%) indicating the importance of man-made emissions in driving the rain water composition and the associated pH around the region.

Influence of south Asian outflow on secondary organic aerosol formation over the Indian Ocean: Inferences from water-soluble low molecular weight dicarboxylic acids and related organic compounds during ICARB 2018 experiment

Low molecular weight dicarboxylic acids constituting a pivotal fraction of organic aerosols impact radiative forcing of Earth's atmosphere. However, a significant knowledge gap exists associated with their sources and formation pathways in the atmosphere. In this study, we report on water-soluble components such as dicarboxylic acids, oxoacids, and α-dicarbonyls as well as carbonaceous and ionic components in the continental outflow from the South Asian region to the Arabian Sea and the equatorial Indian Ocean during ICARB (Integrated Campaign for Aerosols, gases and Radiation Budget) 2018 experiment. Non-sea-salt sulfate (nss SO42−) was found to be the predominant component, followed by ammonium (NH4+) and organic carbon (OC) in fine-sized (<1.1 μm) aerosols. Total diacids carbon content accounted for 17% (on average) of total carbon (TC). Oxalic acid (C2) was the most abundant organic acid, contributing ~41% to total diacids, followed by terephthalic acid (tPh) and succinic acid (C4). Of these results, together with selected organic and inorganic mass ratios and linear relationships among the organic acids, we highlight the sources of organic acids over Indian Ocean. Over continental outflow regions in Indian Ocean, dicarboxylic acids are majorly derived from the emissions of biomass burning and combustion related sources, that underwent transformation in the atmosphere through photochemical reactions during the long range transport. However, over the deep oceanic environment of Indian Ocean, photo-oxidation of biogenic unsaturated fatty acids were found to be the important sources. The findings from this study will be helpful to improve further our understanding of the sources and formation processes of organic aerosols and their climate effects over the South Asian outflow regions.

Measurement report: Firework impacts on air quality in Metro Manila, Philippines, during the 2019 New Year revelry

Abstract. Fireworks degrade air quality, reduce visibility, alter atmospheric chemistry, and cause short-term adverse health effects. However, there have not been any comprehensive physicochemical and optical measurements of fireworks and their associated impacts in a Southeast Asia megacity, where fireworks are a regular part of the culture. Size-resolved particulate matter (PM) measurements were made before, during, and after New Year 2019 at the Manila Observatory in Quezon City, Philippines, as part of the Cloud, Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex). A high-spectral-resolution lidar (HSRL) recorded a substantial increase in backscattered signal associated with high aerosol loading ∼440 m above the surface during the peak of firework activities around 00:00 (local time). This was accompanied by PM2.5 concentrations peaking at 383.9 µg m−3. During the firework event, water-soluble ions and elements, which affect particle formation, growth, and fate, were mostly in the submicrometer diameter range. Total (&gt;0.056 µm) water-soluble bulk particle mass concentrations were enriched by 5.7 times during the fireworks relative to the background (i.e., average of before and after the firework). The water-soluble mass fraction of PM2.5 increased by 18.5 % above that of background values. This corresponded to increased volume fractions of inorganics which increased bulk particle hygroscopicity, kappa (κ), from 0.11 (background) to 0.18 (fireworks). Potassium and non-sea-salt (nss) SO42- contributed the most (70.9 %) to the water-soluble mass, with their mass size distributions shifting from a smaller to a larger submicrometer mode during the firework event. On the other hand, mass size distributions for NO3-, Cl−, and Mg2+ (21.1 % mass contribution) shifted from a supermicrometer mode to a submicrometer mode. Being both uninfluenced by secondary aerosol formation and constituents of firework materials, a subset of species were identified as the best firework tracer species (Cu, Ba, Sr, K+, Al, and Pb). Although these species (excluding K+) only contributed 2.1 % of the total mass concentration of water-soluble ions and elements, they exhibited the highest enrichments (6.1 to 65.2) during the fireworks. Surface microscopy analysis confirmed the presence of potassium/chloride-rich cubic particles along with capsule-shaped particles in firework samples. The results of this study highlight how firework emissions change the physicochemical and optical properties of water-soluble particles (e.g., mass size distribution, composition, hygroscopicity, and aerosol backscatter), which subsequently alters the background aerosol's respirability, influence on surroundings, ability to uptake gases, and viability as cloud condensation nuclei (CCN).

Distributions of water-soluble ions in size-aggregated aerosols over the Southern Ocean and coastal Antarctica.

To investigate mass size distributions of water-soluble ions in aerosols in the marine boundary layer (MBL) over the Southern Ocean, size-segregated (0.056-18 μm in aerodynamic diameter) aerosols were collected on the 28th Chinese National Antarctic Research Expedition (CHINARE) cruise from November 2011 to March 2012. Major water-soluble inorganic and organic species in aerosols were analyzed by ion chromatography (IC). Results showed that high loadings of aerosol mass were observed over the western sector of the Southern Ocean, attributed to the high mass loadings of Na+ and Cl- in the particles >1.0 μm in diameter and high mass loadings of non-sea-salt (nss) SO42- and methanesulfonate (MSA) in the particles <1.0 μm in diameter. Nss-SO42- and MSA accounted for ∼40% of the total mass in aerosols with particle size <0.56 μm over the eastern sector of the Southern Ocean, while it was elevated to more than 60% over the western sector of the Southern Ocean that could be linked with high marine productivity reflected by high chlorophyll-a occurrence in surface waters in that region. MSA/nss-SO42- ratios showed an increasing trend as latitude increased in the southern hemisphere with a dramatic increase south of 60 °S and the variation of MSA may shape the spatial distribution of the ratios. High MSA concentration and MSA/nss-SO42- ratios were observed in west Antarctica, especially in the supermicron particles. A bimodal mass size distribution of total Ca2+ with a small peak in the 0.18-0.32 μm size range was observed, suggesting different sea spray aerosol (SSA) production mechanisms. Nss-SO42-, MSA was mainly enriched in the particle size range of 0.18 μm to 0.56 μm. The concentrations of formate and oxalate were low and detected only in certain size particles, mainly in the range <0.56-1.8 μm. Further studies should be conducted over the remote Southern Ocean to reveal marine ecosystem-aerosol-climate interactions.

Characteristics of methanesulfonic acid, non-sea-salt sulfate and organic carbon aerosols over the Amundsen Sea, Antarctica

Abstract. To investigate the characteristics of particulate methanesulfonic acid (MSA(p)), non-sea-salt sulfate (nss SO42-) and organic carbon (OC) aerosols, aerosol and seawater samples were collected over the Southern Ocean (43–70∘ S) and the Amundsen Sea (70–75∘ S) during the ANA06B cruise conducted in the austral summer of 2016 aboard the Korean icebreaker IBR/V Araon. Over the Southern Ocean, the atmospheric MSA(p) concentration was low (0.10±0.002 µg m−3), whereas its concentration increased sharply up to 0.57 µg m−3 in the Amundsen Sea where Phaeocystis antarctica (P. antarctica), a producer of dimethylsulfide (DMS), was the dominant phytoplankton species. Unlike MSA(p), the mean nss SO42- concentration in the Amundsen Sea was comparable to that in the Southern Ocean. Water-soluble organic carbon (WSOC) concentrations over the Southern Ocean and the Amundsen Sea varied from 0.048 to 0.16 and 0.070 to 0.18 µgC m−3, with averages of 0.087±0.038 and 0.097±0.038 µgC m−3, respectively. For water-insoluble organic carbon (WIOC), its mean concentrations over the Southern Ocean and the Amundsen Sea were 0.25±0.13 and 0.26±0.10 µgC m−3, varying from 0.083 to 0.49 and 0.12 to 0.38 µgC m−3, respectively. WIOC was the dominant organic carbon species in both the Southern Ocean and the Amundsen Sea, accounting for 73 %–75 % of the total aerosol organic carbon. WSOC/Na+ and WIOC/Na+ ratios in the fine-mode aerosol particles were higher, especially in the Amundsen Sea where biological productivity was much higher than the Southern Ocean. The fluorescence properties of water-soluble organic aerosols investigated using a fluorescence excitation–emission matrix coupled with parallel factor analysis (EEM–PARAFAC) revealed that protein-like components were dominant in our marine aerosol samples, representing 69 %–91 % of the total intensity. Protein-like components also showed a significant positive relationship with the relative biomass of diatoms; however, they were negatively correlated with the relative biomass of P. antarctica. These results suggest that the protein-like component is most likely produced as a result of biological processes of diatoms in the Amundsen Sea.

Seasonal Variations in Western North Atlantic Remote Marine Aerosol Properties

AbstractThe impact of ocean ecosystems on marine boundary layer aerosols and clouds has been the subject of much research but remains uncertain. Five experiments were recently conducted in the western North Atlantic to assess if the seasonally recurring phytoplankton bloom affects aerosol properties. These experiments include the second Western Atlantic Climate Study and four North Atlantic Aerosols and Marine Ecosystem Study cruises. Measurements of unheated and heated number size distributions, cloud condensation nucleus (CCN) concentrations, and aerosol composition were used to identify primary and secondary aerosol components that could be related to the state of the bloom. Only periods of clean marine air, as defined by radon, particle number concentrations, aerosol light absorption coefficient, and back trajectories, were included in the analysis. Nonvolatile material was found to be prevalent in the Aitken mode size range after heating to 230°, likely due to downward mixing from the free troposphere. CCN concentrations at 0.1% supersaturation were best correlated (r2 = 0.73) with accumulation mode nss SO4=. Sea spray aerosol was only correlated with CCN during November when bloom accumulation had not yet occurred and dimethylsulfide concentrations were at a minimum. The fraction of CCN attributable to sea spray aerosol was less than 20% during March, May/June, and September, indicating the limited contribution of sea spray aerosol to the CCN population of the western North Atlantic atmosphere. The strongest link between the plankton bloom and aerosol and cloud properties appears to be due to biogenic non‐sea salt SO4=.

Water-Soluble Ionic Characteristics of Aerosols in the Marine Boundary Layer over the Yellow Sea during the KORUS-AQ Campaign

Major compositions of water-soluble ionic species in particulate matter less than 10 and 2.5 μm in diameter (PM10 and PM2.5, respectively) over the Yellow Sea were collected during the Korea–United States Air Quality (KORUS-AQ) campaign in 2016 onboard the research vessel Gisang 1. The secondary ionic species (NH4+, nss-SO42−, and NO3−) in PM10 and PM2.5 accounted for 84% and 89% of the total analyzed species. NH4+ was strongly correlated with non-sea salt (nss) SO42− (nss-SO42−) in PM10 and PM2.5; NO3− was closely correlated with Na+, Mg2+, and nss-Ca2+ in PM10 and NH4+ in PM2.5. High mass concentrations of methane sulfonic acid (MSA, CH3SO3−), the main source of natural sulfates over the Yellow Sea, were observed. The concentrations of MSA were found to show an increasing trend over the Yellow Sea in recent years. Biogenic sulfur contributions to the total nss-SO42− (MSA/nss-SO42− ratio) over the Yellow Sea ranged from 1.4% to 9.2% in PM10 and from 0.68% to 9.5% in PM2.5 during the cruise. Thus, biogenic nss-SO42− must be included, especially in the spring and early summer seasons, when biological activities are elevated in Northeast Asia. We classified the high aerosol mass concentration cases such as Asian dust and haze cases. In Asian dust cases, the ratio of NO3− to nss-SO42− in the aerosols showed that mobile (stationary) sources mainly affected PM10 (PM2.5). The major chemical species for Asian dust cases over the Yellow sea were CaCO3, Ca(NO3)2, Mg(NO3)2, Na(NO3)2, and sea salt. In haze cases over the Yellow sea, the contributions from stationary sources are high and the major species were (NH4)2SO4 and NH4NO3 in PM10 and PM2.5, respectively.

Morphological features and mixing states of soot-containing particles in the marine boundary layer over the Indian and Southern oceans

Abstract. Mixing states of soot-containing aerosol particles constitute important information for the simulation of climatic effects of black carbon in the atmosphere. To elucidate the mixing states and morphological features of soot-containing particles over remote oceans, we conducted on-board observations over the southern Indian Ocean and the Southern Ocean during the TR/V Umitaka-maru UM-08-09 cruise, which started from Benoa, Indonesia, on 1 December 2008 via Cape Town, South Africa, and which terminated in Fremantle, Australia, on 6 February 2009. The light absorption coefficients of size-segregated particles (&lt; 0.5 and &lt; 1.0 µm diameter) and aerosol number concentrations (0.1–0.5 µm diameter) were measured to assist direct aerosol sampling. Size-segregated aerosol particles were collected for chemical analysis using ion chromatography. For transmission electron microscopy (TEM) analyses using water-dialysis methods, dried submicrometer aerosol particles were collected using a cascade impactor. We analyzed 13 TEM samples. Results of water-dialysis analysis demonstrate that most particles were water-soluble. However, for all TEM samples, particles were rarely found (2.1 % of particles on a TEM sample at a maximum) containing insoluble residuals with the characteristic soot shape. For samples collected over the Indian and Southern oceans at latitudes less than 62∘ S, some (20–35 %) soot-containing particles were found as bare soot. For samples collected near the Antarctic coast (65–68∘ S, 38–68∘ E), all soot-containing particles were mixed with water-soluble materials. Furthermore, 56 % of soot-containing particles had a satellite structure formed by the impact of droplets such as sulfuric acid. Chemical analysis of submicrometer particles near the Antarctic coast revealed high concentrations of non-sea-salt (nss) SO42- and CH3SO3-, suggesting that aged soot-containing particles were transformed by soluble materials derived from dimethyl sulfide (DMS) oxidation. The obtained information of soot at various remote ocean areas is expected to be useful to understand long-range transport processes and to improve simulations of global soot concentration.

Size distribution and ionic composition of marine summer aerosol at the continental Antarctic site Kohnen

Abstract. We measured aerosol size distributions and conducted bulk and size-segregated aerosol sampling during two summer campaigns in January 2015 and January 2016 at the continental Antarctic station Kohnen (Dronning Maud Land). Physical and chemical aerosol properties differ conspicuously during the episodic impact of a distinctive low-pressure system in 2015 (LPS15) compared to the prevailing clear sky conditions. The approximately 3-day LPS15 located in the eastern Weddell Sea was associated with the following: marine boundary layer air mass intrusion; enhanced condensation particle concentrations (1400 ± 700 cm−3 compared to 250 ± 120 cm−3 under clear sky conditions; mean ± SD); the occurrence of a new particle formation event exhibiting a continuous growth of particle diameters (Dp) from 12 to 43 nm over 44 h (growth rate 0.6 nm h−1); peaking methane sulfonate (MS−), non-sea-salt sulfate (nss–SO42-), and Na+ concentrations (190 ng m−3 MS−, 137 ng m−3 nss–SO42-, and 53 ng m−3 Na+ compared to 24 ± 15, 107 ± 20, and 4.1 ± 2.2 ng m−3, respectively, during clear sky conditions); and finally an increased MS− ∕ nss–SO42- mass ratio βMS of 0.4 up to 2.3 (0.21 ± 0.1 under clear sky conditions) comparable to typical values found at coastal Antarctic sites. Throughout the observation period a larger part of MS− could be found in super-micron aerosol compared to nss–SO42-, i.e., (10 ± 2) % by mass compared to (3.2 ± 2) %, respectively. On the whole, under clear sky conditions aged aerosol characterized by usually mono-modal size distributions around Dp= 60 nm was observed. Although our observations indicate that the sporadic impacts of coastal cyclones were associated with enhanced marine aerosol entry, aerosol deposition on-site during austral summer should be largely dominated by typical steady clear sky conditions.

A 60 Year Record of Atmospheric Aerosol Depositions Preserved in a High‐Accumulation Dome Ice Core, Southeast Greenland

AbstractThe Southeastern Greenland Dome (SE‐Dome) has both a high elevation and a high accumulation rate (1.01 m we yr−1), which are suitable properties for reconstructing past environmental changes with a high time resolution. For this study, we measured the major ion fluxes in a 90 m ice core drilled from the SE‐Dome region in 2015 and present the records of annual ion fluxes from 1957 to 2014. From 1970 to 2010, the trend of nonsea‐salt (nss) SO42− flux decreases, whereas that for NH4+ increases, tracking well with the anthropogenic SOx and NH3 emissions mainly from North America. The result suggests that these fluxes reflect histories of the anthropogenic SOx and NH3 emissions. In contrast, the decadal trend of NO3− flux differs from the decreasing trend of anthropogenic NOx emissions. Although the cause of this discrepancy remains unclear, it may be related to changes in particle formation processes and chemical scavenging rates caused by an increase in sea salt and dust and/or a decrease in nssSO42−. We also find a high average NO3− flux (1.13 mmol m−2 yr−1) in the ice core, which suggests a negligible effect from postdepositional NO3− loss. Thus, the SE‐Dome region is an excellent location for reconstructing nitrate fluxes. Over a decadal time scale, our NO3− flux record is similar to those from other ice cores in Greenland high‐elevation sites, suggesting that NO3− concentration records from these ice cores are reliable.

Atmospheric Wet Deposition in Remote Regions: Benchmarks for Environmental Change

Abstract Precipitation composition was characterized at 14 remote sites between 65°N and 51°S. Anthropogenic sources contributed to non-sea-salt (nss) SO42−, NO3−, and NH4+ in North Atlantic precipitation. Biogenic sources accounted for 0.4–3.3 μeq L−1 of volume-weighted-average (VWA) nss SO42− in marine precipitation. SO42− at the continental sites (2.9–7.7 μeq L−1) was generally higher. VWA NO3− (0.5–1.3 μeq L−1) and NH4+ (0.5–2.6 μeq L−1) at marine-influenced, Southern Hemispheric sites were generally less than those at continental sites (1.4–4.8 μeq L−1 and 2.3–4.2 μeq L−1, respectively). VWA pH ranged from 4.69 to 5.25. Excluding the North Atlantic, nss SO42−, NO3−, and NH4+ wet depositions were factors of 4–47, 5–61, and 3–39, respectively, less than those in the eastern United States during 2002–04. HCOOHt (HCOOHaq + HCOO−) and CH3COOHt (CH3COOHaq + CH3COO−) concentrations and depositions at marine sites overlapped, implying spatially similar source strengths from marine-derived precursors. Greater variability at continental sites suggests heterogeneity in terrestrial source strengths. Seasonality in deposition was driven by variability in precipitation amount, wind velocity, transport, and emissions. Between 1980 and 2009, nss SO42− at Bermuda decreased by 85% in response to decreasing U.S. SO2 emissions; trends in NO3− and NH4+ were inconsequential. Corresponding decreases in acidity, as reflected in the significant 30% decline in VWA H+, impacted pH-dependent chemical processes. Comparisons between measurements and models indicate that current predictive capabilities are uncertain by factors of 2 or more.

Analysis of a decade of Asian outflow of PM10 and TSP to Gosan, Korea; also incorporating Radon–222

Ten years of aerosol and Radon–222 (radon) data from Gosan, Korea, were analyzed. Seasonal cycles were strongly linked to changes in fetch and time of year. We estimated that 7.21t/m y of PMio aerosol pass Gosan in the atmospheric boundary layer, increasing annually by 0.3t/m y. Contributions to aerosol loading were characterized by fetch: South China, North China, Korea and Japan. While the highest, and most variable, contributions typically originated from South China, these air masses contributed to only 6% of the overall dataset. PM10 distributions were broader from South and North China than for Korea or Japan, reflecting differences in natural/anthropogenic soil sources, and number/distribution of large point sources. Employing radon to select air masses more representative of targeted fetch regions typically resulted in greater reported pollutant concentrations and rates of change over the decade. Estimated rates of PM10 increase from North China and Korea over the decade were 1.4 and 0.9μg/m3 y, respectively. Total suspended particulate (TSP) elemental analysis indicated that the (non–sea–salt) nss–SO42− content of aerosols has been gradually increasing over the past decade and more recently an increase in NO3− was seen. However, on average, rates of increase in nss–SO42− have reduced since 2007, which were higher in South than North China.

Characterization of marine aerosols and precipitation through shipboard observations on the transect between 31° N–32° S in the West Pacific

To characterize the chemical composition, size distributions, and fractional Fe solubility of atmospheric particles over Asian marginal seas, South Indian Ocean and Australian coast, selected water–soluble inorganic and organic species in aerosols and precipitation, trace metals and soluble Fe in aerosols were analyzed by multi–instruments. Results showed that sea salt and non–sea–salt sulfate (nss–SO42–) were the main components in aerosols. Over Asian marginal seas, Cl– and Na+ were the dominant ions in precipitation, accounting for ˜;72% of the total ions. Both SO42– and NO3– accounted for −26% of the total anions, controlling the acidity of the precipitation. Non–sea–salt Ca2+ (nss–Ca2+) accounted for 6.9% of the total cations, dominating the neutralizing component in rainwater. Observed methane sulfonate (MSA) concentrations and MSA/nss–SO42– increased southward. The concentrations of sea salt were affected by wind speeds, which was mainly accumulated in particle size >10μm. Particle size distributions of nss–SO42– and NH4+ mainly peaked in the fine mode, while NO3– was mainly accumulated in the coarse mode. Oxalate presented a bimodal size distribution pattern in both fine and coarse modes. Based on the air mass back trajectories, enrichment factors and Fe/Al, V/Al ratios, aerosol samples collected over Asian marginal seas could be affected by both long–range transported dust and anthropogenic emissions. Good relationship was found between total dissolved iron and nss–SO42–, indicating that acid processing during long–range transport could play an important role in fractional iron solubility in aerosols. The inverse relationship between atmospheric total Fe and fractional Fe solubility fitted in the global–scale trend. This study implicates that dust and acidic air pollutants from continental sources can interact and affect iron solubility in aerosols in the marine atmosphere. However, due to the small size of samples in this study, more investigations need to be conducted in future.

Long-term trends in aerosol and precipitation composition over the western North Atlantic Ocean at Bermuda

Abstract. Since the 1980s, emissions of SO2 and NOx (NO + NO2) from anthropogenic sources in the United States (US), Canada, and Europe have decreased significantly suggesting that the export of oxidized S and N compounds from surrounding continents to the atmosphere overlying the North Atlantic Ocean (NAO) has also decreased. The chemical compositions of aerosols and precipitation sampled daily on Bermuda (32.27° N, 64.87° W) from 1989 to 1997 and from 2006 to 2009 were evaluated to quantify the magnitudes, significance, and implications of associated tends in atmospheric composition. The chemical data were stratified based on FLEXPART (FLEXible PARTicle dispersion model) retroplumes into four discrete transport regimes: westerly flow from eastern North America (NEUS/SEUS); easterly trade-wind flow from northern Africa and the subtropical NAO (Africa); long, open-ocean, anticyclonic flow around the Bermuda High (Oceanic); and transitional flow from the relatively clean open ocean to the polluted eastern North America (North). Based on all data, annual average concentrations of non-sea-salt (nss) SO42– associated with aerosols and annual volume-weighted-average (VWA) concentrations in precipitation decreased significantly (by 22% and 49%, respectively) whereas annual VWA concentrations of NH4+ in precipitation increased significantly (by 70%). Corresponding trends in aerosol and precipitation NO3– and of aerosol NH4+ were insignificant. Nss SO42– in precipitation under NEUS/SEUS and Oceanic flow decreased significantly (61% each) whereas corresponding trends in particulate nss SO42– under both flow regimes were insignificant. Trends in precipitation composition were driven in part by decreasing emissions of SO2 over upwind continents and associated decreases in anthropogenic contributions to nss SO42– concentrations. Under NEUS/SEUS and Oceanic flow, the ratio of anthropogenic to biogenic contributions to nss SO42– in the column scavenged by precipitation were relatively greater than those in near surface aerosol, which implies that, for these flow regimes, precipitation is a better indicator of overall anthropogenic impacts on the lower troposphere. Particulate nss SO42– under African flow also decreased significantly (34%) whereas the corresponding decrease in nss SO42– associated with precipitation was insignificant. We infer that these trends were driven in part by reductions in the emissions and transport of oxidized S compounds from Europe. The lack of significant trends in NO3– associated with aerosols and precipitation under NEUS/SEUS flow is notable in light of the large decrease (37%) in NOx emissions in the US and Canada over the period of record. Rapid chemical processing of oxidized N in marine air contributed to this lack of correspondence. Decreasing ratios of nss SO42– to NH4+ and the significant decreasing trend in precipitation acidity (37%) indicate that the total amount of acidity in the multiphase gas–aerosol system in the western NAO troposphere decreased over the period of record. Decreasing aerosol acidities would have shifted the phase partitioning of total NH3 (NH3 + particulate NH4+ towards the gas phase thereby decreasing the atmospheric lifetime of total NH3 against wet plus dry deposition. The trend of increasing NH4+ in precipitation at Bermuda over the period of record suggests that NH3 emissions from surrounding continents also increased. Decreasing particulate nss SO42– in near-surface air under NEUS/SEUS flow over the period of record implies that the corresponding shortwave scattering and absorption by nss S and associated aerosols constituents also decreased. These changes in radiative transfer suggest a corresponding lower limit for net warming over the period in the range of 0.1–0.3 W m–2.

Effects of ship emissions on summertime aerosols at Ny–Alesund in the Arctic

Selected trace elements, ionic species and organic/elemental carbon in aerosols were measured in summer at Ny–Alesund in the Arctic, and an interpreted approach combining elemental ratios, back–trajectories and enrichment factors was used to assess the sources of aerosols observed at this location. Aerosol samples influenced by ship emissions were featured by elevated concentrations of non–crustal (nc) vanadium (V), nc–nickel (nc–Ni), non–sea salt (nss) sulfate (SO42−) and ratios of nc–Ni/nc–V (1.7) and nss–SO42−/nc–V (200). When two cruise ships with more than 1 500 passengers visited Ny–Alesund in July 2012, the total suspended particulate (TSP) mass reached 2 290ng m−3, almost three times the median TSP concentration (609ng m−3) measured during the study period. The nc–V concentration reached 0.976ng m−3, about 38–fold higher compared to the mean value of the sampling period, and this value was even higher than the annual mean value observed at Zeppelin station and the values measured during Haze events at North American Arctic and Norwegian Arctic. The concentrations of nc–Ni and nss–SO42− were 0.572ng m−3 and 203ng m−3, which were 8–fold and 2–fold higher than the median values of the sampling period. While in the few–ship period, defined as the period with none or only one cruise ship with less than 1 000 passengers being present, aerosols at this location could be affected by a mixed impact of local emissions and long–range transport, reflected by the nc–Mn/nc–V ratios and element enrichment factors often found in the air masses from North America Arctic, Iceland and North Eurasia. Results from this study suggest that cruise ship emissions contributed significantly to atmospheric particulate matter at Ny–Alesund in the summer, effecting air quality in this area.

Sensitivity of tropospheric chemical composition to halogen-radical chemistry using a fully coupled size-resolved multiphase chemistry–global climate system: halogen distributions, aerosol composition, and sensitivity of climate-relevant gases

Abstract. Observations and model calculations indicate that highly non-linear multiphase atmospheric processes involving inorganic Cl and Br significantly impact tropospheric chemistry and composition, aerosol evolution, and radiative transfer. The sensitivity of global atmospheric chemistry to the production of marine aerosol and the associated activation and cycling of inorganic Cl and Br was investigated using a size-resolved multiphase coupled chemistry–global climate model (National Center for Atmospheric Research's Community Atmosphere Model (CAM) v3.6.33). Simulated results revealed strong meridional and vertical gradients in Cl and Br species. They also point to possible physicochemical mechanisms that may account for several previously unexplained phenomena, including the enrichment of Br- in submicron aerosol and the presence of a BrO maximum in the polar free troposphere. However, simulated total volatile inorganic Br mixing ratios in the troposphere were generally higher than observed, due in part to the overly efficient net production of BrCl. In addition, the emission scheme for marine aerosol and associated Br−, which is the only source for Br in the model, overestimates emission fluxes from the high-latitude Southern Ocean. Br in the stratosphere was lower than observed due to the lack of long-lived precursor organobromine species in the simulation. Comparing simulations using chemical mechanisms with and without reactive Cl and Br species demonstrates a significant temporal and spatial sensitivity of primary atmospheric oxidants (O3, HOx, NOx), CH4, non-methane hydrocarbons (NMHCs), and dimethyl sulfide (DMS) to halogen cycling. Globally, halogen chemistry had relatively less impact on SO2 and non-sea-salt (nss) SO42− although significant regional differences were evident. Although variable geographically, much of this sensitivity is attributable to either over-vigorous activation of Br (primarily BrCl) via the chemical mechanism or overproduction of sea-salt aerosol simulated under higher-wind regimes. In regions where simulated mixing ratios of reactive Br and Cl fell within observed ranges, though, halogen chemistry drove large changes in oxidant fields and associated chemical processes relative to simulations with no halogens. However, the overall simulated impacts of Br chemistry globally are overestimated and thus caution is warranted in their interpretation.

Flow climatology for physicochemical properties of dichotomous aerosol over the western North Atlantic Ocean at Bermuda

Abstract. Dichotomous aerosols (nominal super- and sub-μm-diameter size fractions) in sectored on-shore flow were sampled daily from July 2006 through June 2009, at the Tudor Hill Atmospheric Observatory (THAO) on the western coast of Bermuda (32.27° N, 64.87° W) and analyzed for major chemical and physical properties. FLEXPART retroplumes were calculated for each sampling period and aerosol properties were stratified accordingly based on transport from different regions. Transport from the northeastern United States (NEUS) was associated with significantly higher (factors of 2 to 3 based on median values) concentrations of bulk particulate non-sea-salt (nss) SO42-, NO3-, and NH4+ and associated scattering and absorption at 530 nm, relative to transport from Africa (AFR) and the oceanic background. These differences were driven primarily by higher values associated with the sub-μm size fraction under NEUS flow. We estimate that 75(±3)% of the NEUS nss SO42- was anthropogenic in origin, while only 25(±9)% of the AFR nss SO42- was anthropogenic. Integrating over all transport patterns, the contribution of anthropogenic sulfate has dropped 14.6% from the early 1990s. Bulk scattering was highly correlated with bulk nss SO42- in all flow regimes but the corresponding regression slopes varied significantly reflecting differential contributions to total scattering by associated aerosol components. Absorption by super-μm aerosol in transport from the NEUS versus AFR was similar although the super-μm aerosol size fraction accounted for a relatively greater contribution to total absorption in AFR flow. Significantly greater absorption Ångström exponents (AAEs) for AFR flow reflects the wavelength dependence of absorption by mineral aerosols; lower AAEs for NEUS flow is consistent with the dominance of absorption by combustion-derived aerosols. Higher AOD associated with transport from both the NEUS and AFR relative to oceanic background flow results in a top of atmosphere direct radiative forcing on the order of −1.6 to −2.5 W m−2, respectively, showing these aerosols drive cooling. The dominance of transport from the NEUS on an annual basis coupled with the corresponding decreases in anthropogenic nss SO42- aerosols since the early 1990s implies that emission reductions in the US account for a decline in atmospheric cooling over the western North Atlantic Ocean during this period.

Characteristics of water‐soluble inorganic and organic ions in aerosols over the Southern Ocean and coastal East Antarctica during austral summer

AbstractTo characterize the concentrations and size distributions of water‐soluble organic and inorganic aerosol species, including Na+, non‐sea‐salt sulfate (nss SO42−), methane sulfonate (MSA), oxalate, and succinate, over the Southern Ocean (SO) and coastal East Antarctica (CEA), bulk and size‐segregated aerosols were collected from 40°S, 100°E to 69°S, 76°E and between 69°S, 76°E and 66°S, 110°E during a cruise from November 2010 to March 2011. Results show that sea salt was the major component of the total aerosol mass, accounting for 72% over the SO and 56% over CEA. The average concentrations of nss SO42− varied from 420 ng m−3 over the SO to 480 ng m−3 over CEA. The concentrations of MSA ranged from 63 to 87 ng m−3 over the SO and from 46 to 170 ng m−3 in CEA. The average concentrations of oxalate were 3.8 ng m−3 over the SO and 2.2 ng m−3 over CEA. The concentrations of formate, acetate, and succinate were lower than those of oxalate. A bimodal size distribution of aerosol mass existed over CEA, peaking at 0.32–0.56 µm and 3.2–5.6 µm. MSA was accumulated in particles of 0.32–0.56 µm over CEA. High chloride depletion was associated with fine‐mode particles enriched with nss SO42−, MSA, and oxalate. Higher cation‐to‐anion and NH4+/nss SO42− ratios in aerosols over CEA compared to that over the SO imply the higher neutralization capacity of the marine atmosphere over CEA.

Lead and sulfur isotopic ratios in precipitation and their relations to trans-boundary atmospheric pollution

We measured the lead (Pb) and sulfur (S) isotopic ratios in precipitation collected in Toyama Prefecture, Japan, to investigate their characteristics as tracers for trans-boundary air pollution. The Pb concentrations and isotopic ratios were measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). A relatively higher 207Pb/206Pb isotopic ratio (area 3: Northern China, 0.869±0.003; area 4: Central China and Korea, 0.870±0.006) was assumed to be related to Northern Asian sources, whereas the samples influenced by Japanese air mass showed a lower 207Pb/206Pb ratio (area 5: Japan, 0.863±0.004). Sulfur ion was measured by Ion Chromatography (IC), and S isotopic ratios were measured by Mass Spectrometry. The S isotopic ratios' weighted average values (area 3: 4.9±1.4‰; area 4: 6.3±1.5‰) of the Asian continent showed a higher isotopic ratio than that of Japan (area 5: 3.6±1.8‰). It was difficult to use the NO3−/non-sea-salt SO42− (nss SO42−) (N/S) ratio's weighted average values to distinguish the Japanese origin (area 5: 0.71) from the continental origin (area 3: 0.68, area 4: 0.66). We attempted to use the S isotopic ratio in addition to the lead isotopic ratio to characterize the transported East Asian air pollution, and as a result we found that the combination of these isotopic ratios was useful for identifying the origin of air pollution in the East Asian region.

Seasonality in size segregated biogenic, anthropogenic and sea salt sulfate aerosols over the North Atlantic

Size segregated aerosol sulfate concentration was measured over a south to north transect of the North Atlantic, extending from 37° N to the base of Greenland, during spring, summer and fall of 2003. Sea salt sulfate for all three seasons was found in large diameter aerosols (>0.95 μm), but spring season sea salt was also persistently found in the finest aerosols collected (<0.49 μm). Non sea salt sulfate concentrations in the 0.49–0.95 μm range (large accumulation mode) were elevated in summer (5.7 ± 7.0 nmol m −3 ) relative to spring (1.4 ± 0.7 nmol m −3 ) and fall (1.3 ± 1.0 nmol m −3 ). Non sea salt sulfate was apportioned into biogenic and anthropogenic sulfate using sulfur isotopes. Little to no biogenic sulfate was observed in the spring. However, in the summer and fall biogenic sulfate concentration averaged 2.3 ± 1.4 nmol m −3 and 2.0 ± 2.2 nmol m −3 respectively in aerosols less than 0.49 μm diameter corresponding to approximately 40% of the non sea salt sulfate load for both seasons. Anthropogenic sulfate was detectable throughout the study with the largest concentrations of fine aerosol anthropogenic sulfate (up to 76 nmol m −3 ) observed in samples collected at lower latitudes. Stable isotopes were used to determine aerosol growth from local SO 2 oxidation in the summer. SO 2 oxidation is calculated to be significant in two aerosol growth events. These samples had the largest biogenic sulfate concentrations in the 0.49–0.95 μm range aerosols and showed high concentrations of sulfate in the 0.49–0.95 μm relative to the <0.49 μm diameter aerosols. Sulfate from local SO 2 oxidation was calculated to be approximately 40% of the non sea salt sulfate present in these two events. ► North Atlantic size segregated aerosol SO 4 concentrations measured over 3 seasons. ► Anthropogenic and biogenic sulfate concentrations determined by isotope apportionment. ► Sea Salt found in <0.49 μm spring aerosols not present in other seasons. ► Elevated summer NSS SO 4 in 0.49 μm–0.95 μm aerosols relative to other seasons. ► Evidence of aerosol growth events from SO 2 oxidation in summer.