Non-sea Salt Sulfate Research Articles

Measurements of particulate methanesulfonic acid above the remote Arctic Ocean using a high resolution aerosol mass spectrometer

Methanesulfonic acid (MSA) is an important product from the oxidation of dimethyl sulfide (DMS), and thus is often used as a tracer for marine biogenic sources and secondary organic aerosol. MSA also contributes to aerosol mass and potentially to the formation of cloud condensation nuclei and new particles. However, measurements of MSA at high temporal resolution in the remote Arctic are scarce, which limits our understanding of its formation, climate change impact and regional transport. Here, we applied a validated quantification method to determine the mass concentration of MSA and non-sea salt sulfate (nss-SO4) in PM2.5 in the marine boundary layer, using a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) during a research cruise to the Arctic and North Atlantic Ocean, between 55 °N and 68 °N (26th May to June 23, 2022). With this method, the concentrations of MSA in the remote Arctic marine boundary layer were determined for the first time. Results show that the average MSA concentration was 0.025 ± 0.03 μg m−3, ranging from <0.01 to 0.32 μg m−3. The lowest MSA level was found towards the northern leg of the cruise (near Sisimut (67 °N)) with air masses from sea ice over the northern polar region, and the highest MSA concentrations were observed over the Atlantic open ocean. The diurnal cycles of gas MSA, particulate MSA and nss-SO4 peaked in the afternoon, about one hour later than that of peak of solar radiation, which suggests that photochemical process is an important mechanism for the conversion of DMS into MSA above the remote ocean. The mass ratio of MSA to nss-SO4 (MSA/nss-SO4) presents a temperature dependence, which indicates that the addition branching pathway favors MSA formation, while thermal decay of intermediate radicals could be a possible pathway for sulfate formation. Finally, we found that the MSA/nss-SO4 ratio is around 0.22-0.25 in the remote northern marine atmosphere.

Sulfate sources, biologic cycling, and mobility in Atacama Desert soils revealed by isotope signatures

A set of 55 surface samples from Atacama Desert gypsisols was collected along four altitude transects and analyzed for ∆17OSO4, δ18OSO4, δ34SSO4, and 87Sr/86Sr in order to identify the main depositional mechanisms and quantify the proportional contribution of sulfate sources across the desert's main topographic units – the Coastal Cordillera, the Central Depression, and the Precordillera. Sulfate deposited at any location in the Atacama Desert may derive from up to five different source and process endmembers that can principally be identified by their isotopic composition. Three aerosol sources dominate sulfate deposition and accumulation in gypsisols throughout the Atacama. These are secondary atmospheric Ca- and Na-sulfate derived from global volcanic SO2 oxidized by ozone and its derivates, and a marine sulfate aerosol that is roughly a 9:1 mixture of sea salt (primary) sulfate from evaporated sea spray, and secondary non-sea salt sulfate, i.e., dimethyl sulfide (DMS) mainly oxidized by ozone. These marine sources dominate sulfate deposition in the Coastal Cordillera. Unlike in most places on Earth, the positive mass-independent ∆17OSO4 signature of secondary atmospheric sulfate is ubiquitous in Atacama Desert soils and is never completely erased by biologic cycling. Hence, biologic cycling of the sulfate inventory – i.e., the reduction of sulfate, subsequent oxygen isotope exchange with water, and re-oxidation – is apparently not quantitative in any of the Atacama Desert environments sampled here, including the most biologically active permanent salt lakes. The preservation of highest ∆17OSO4 values (∼ 1.0‰) at altitudes of the Coastal Cordillera above the 1200 m altitude cut-off level of fog advection suggest that episodic rainfall events are insufficient for significant in situ biologic sulfate turnover. At lower altitudes and regular fog advection, moisture supply appears to be sufficient for limited in situ biologic sulfate turnover. Overall, biologically recycled sulfate constitutes a fourth major contributor to the desert's gypsisol sulfate inventory. This may comprise fluvially redeposited sulfate from older sediments, particularly on the debris fans protruding from the Precordillera into the Central Depression. In the Central Depression, Sr-isotopes may allow for a further distinction between redeposition-dominated and aerosol-dominated sedimentation environments. On the Precordillera, rainfall and run-off provide sufficient moisture for significant but still incomplete in situ biologic sulfate cycling. Hydrothermal non-evaporitic Na-sulfate – the fifth potential source – likely originates from larger outflow events or mobilization from rock veins over the course of the Atacama's geologic history may contribute locally to the sulfate inventory. The degree of bio-cycling and mobility of sulfate likely reflects a balance between overall water availability and the mixing proportion of very soluble (mobile) Na-sulfate and less soluble Ca-sulfate inherent in the various sulfate sources.

Atmospheric Deposition around the Industrial Areas of Milazzo and Priolo Gargallo (Sicily-Italy)-Part A: Major Ions.

The chemical composition of rainwater was studied in two highly-industrialised areas in Sicily (southern Italy), between June 2018 and July 2019. The study areas were characterised by large oil refining plants and other industrial hubs whose processes contribute to the release of large amounts of gaseous species that can affect the chemical composition of atmospheric deposition As in most of the Mediterranean area, rainwater acidity (ranging in the study area between 3.9 and 8.3) was buffered by the dissolution of abundant geogenic carbonate aerosol. In particular, calcium and magnesium cations showed the highest pH-neutralizing factor, with ~92% of the acidity brought by SO42- and NO3- neutralized by alkaline dust. The lowest pH values were observed in samples collected after abundant rain periods, characterised by a less significant dry deposition of alkaline materials. Electrical Conductivity (ranging between 7 µS cm-1 and 396 µS cm-1) was inversely correlated with the amount of rainfall measured in the two areas. Concentrations of major ionic species followed the sequence Cl- > Na+ > SO42- ≃ HCO3- > ≃ Ca2+ > NO3- > Mg2+ > K+ > F-. High loads of Na+ and Cl- (with a calculated R2 = 0.99) reflected proximity to the sea. Calcium, potassium, and non-sea-salt magnesium had a prevalent crustal origin. Non-sea salt sulphate, nitrate, and fluoride can be attributed mainly to anthropogenic sources. Mt. Etna, during eruptive periods, may be also considered, on a regional scale, a significant source for fluoride, non-sea salt sulphate, and even chloride.

Climate Roles of Non-Sea Salt Sulfate and Sea Spray Aerosol in the Atmospheric Marine Boundary Layer: Highlights of 40 Years of PMEL Research

The Pacific Marine Environmental Laboratory (PMEL) began measurements of dimethylsulfide (DMS) in 1982 to better understand the seawater sulfur cycle and the contribution of seawater DMS emissions to the global atmospheric sulfur budget. These measurements led to a global ocean database of DMS seawater concentrations currently hosted at PMEL, with contributions from researchers worldwide. In the mid-1980s, PMEL followed DMS from the ocean into the atmosphere and began aerosol measurements. It was found that DMS-derived, biogenic sulfate can make up a large fraction of the submicron aerosol in the remote marine atmosphere. In addition, it was found that a significant and variable fraction of submicron aerosol over the ocean was composed not only of biogenic sulfate but also included sea spray aerosol and long-range transported components. These measurements were pioneering in providing evidence that marine aerosols are a complex mixture of chemical components that should be included in climate models in order to accurately model Earth’s radiation budget. Measurements from 27 cruises have helped form a coherent view of species responsible for aerosol light scattering and cloud drop nucleation in the marine boundary layer. This global database of aerosol properties is publicly available on PMEL web pages for use by the modeling and satellite communities. Most recently, PMEL has developed payloads for uncrewed aerial systems to extend surface shipboard measurements up to 3,000 m in altitude and to include measurements of cloud properties.

Small contributions of dust to PM2.5 and PM10 concentrations measured downwind of Oceano Dunes

The Oceano Dunes State Vehicular Recreation Area (ODSVRA) is a large natural source of wind-driven dust emissions that primarily consist of particulate matter (PM) for which most of the mass is greater than 1 μm. The San Luis Obispo County Air Pollution Control District (SLOAPCD) has targeted ODSVRA emissions to reduce exceedances of the state standard of 50 μg m−3 for PM smaller than 10 μm (PM10) at a coastal monitoring site located 1 mile downwind of the dune area. To evaluate the potential effectiveness of this abatement strategy, five sets of measurements were collected during the windy afternoons of high-wind months (May and October) from 2019 to 2021 to quantify the organic and elemental composition of PM10 and PM smaller than 2.5 μm (PM2.5) samples. The five-campaign average afternoon PM2.5 composition relative to Beta Attenuation Monitor (BAM) concentrations included 14 ± 12% dust, 9 ± 9% sea salt, 4 ± 5% non-sea salt sulfate, and 8 ± 8% organic components, with the difference between BAM and the measured components contributing the remaining 66 ± 16% unidentified components. The high afternoon unidentified contribution was partially attributable to water, consistent with the increasing relative humidity during warm afternoons, since there was a lower unidentified contribution for overnight samples. The remaining unidentified components are consistent with prior measurements of semivolatile contributions of ammonium nitrate and organic compounds constituting >40% of PM2.5 in central California. The organic functional group signature in Fourier Transform Infrared (FTIR) spectroscopy for PM2.5 was similar to previously reported ambient marine aerosol, consistent with a natural marine source for most of the organic mass concentration. For PM10, the dust fraction was 11 ± 8% of BAM PM10 concentration and increased to 14 ± 10% of BAM PM10 concentration during days in which hourly BAM PM10 concentration exceeded 140 μg m−3. There was no statistically significant difference (p»0.05) between dust, sea salt, sulfate, or organic PM2.5 fractions between weekend and weekday concentrations, similar to prior findings for the region. These results are consistent with national and state assessments of the good air quality of the region and suggest that semivolatile components may cause differences between BAM and gravimetric mass concentrations for sampling times shorter than 24 h. In addition, the results demonstrate that the regulated dust abatement implemented at ODSVRA is misapplied and unlikely to improve downwind air quality significantly, since ODSVRA and other nearby sandy areas contribute only 14% of BAM PM10 and have not been shown to include toxic components.

Measurement report: Closure analysis of aerosol–cloud composition in tropical maritime warm convection

Abstract. Cloud droplet chemical composition is a key observable property that can aid understanding of how aerosols and clouds interact. As part of the Clouds, Aerosols and Monsoon Processes – Philippines Experiment (CAMP2Ex), three case studies were analyzed involving collocated airborne sampling of relevant clear and cloudy air masses associated with maritime warm convection. Two of the cases represented a polluted marine background, with signatures of transported East Asian regional pollution, aged over water for several days, while the third case comprised a major smoke transport event from Kalimantan fires. Sea salt was a dominant component of cloud droplet composition, in spite of fine particulate enhancement from regional anthropogenic sources. Furthermore, the proportion of sea salt was enhanced relative to sulfate in rainwater and may indicate both a propensity for sea salt to aid warm rain production and an increased collection efficiency of large sea salt particles by rain in subsaturated environments. Amongst cases, as precipitation became more significant, so too did the variability in the sea salt to (non-sea salt) sulfate ratio. Across cases, nitrate and ammonium were fractionally greater in cloud water than fine-mode aerosol particles; however, a strong covariability in cloud water nitrate and sea salt was suggestive of prior uptake of nitrate on large salt particles. A mass-based closure analysis of non-sea salt sulfate compared the cloud water air-equivalent mass concentration to the concentration of aerosol particles serving as cloud condensation nuclei for droplet activation. While sulfate found in cloud was generally constrained by the sub-cloud aerosol concentration, there was significant intra-cloud variability that was attributed to entrainment – causing evaporation of sulfate-containing droplets – and losses due to precipitation. In addition, precipitation tended to promote mesoscale variability in the sub-cloud aerosol through a combination of removal, convective downdrafts, and dynamically driven convergence. Physical mechanisms exerted such strong control over the cloud water compositional budget that it was not possible to isolate any signature of chemical production/loss using in-cloud observations. The cloud-free environment surrounding the non-precipitating smoke case indicated sulfate enhancement compared to convective mixing quantified by a stable gas tracer; however, this was not observed in the cloud water (either through use of ratios or the mass closure), perhaps implying that the warm convective cloud timescale was too short for chemical production to be a leading-order budgetary term and because precursors had already been predominantly exhausted. Closure of other species was truncated by incomplete characterization of coarse aerosol (e.g., it was found that only 10 %–50 % of sea salt mass found in cloud was captured during clear-air sampling) and unmeasured gas-phase abundances affecting closure of semi-volatile aerosol species (e.g., ammonium, nitrate and organic) and soluble volatile organic compound contributions to total organic carbon in cloud water.

Factors controlling atmospheric DMS and its oxidation products (MSA and nssSO42−) in the aerosol at Terra Nova Bay, Antarctica

Abstract. This paper presents the results of simultaneous high time-resolution measurements of biogenic aerosol (methane sulfonic acid (MSA), non-sea salt sulfate nssSO42-) with its gaseous precursor dimethylsulfide (DMS), performed at the Italian coastal base Mario Zucchelli Station (MZS) in Terra Nova Bay (MZS) during two summer campaigns (2018–2019 and 2019–2020). Data on atmospheric DMS concentration are scarce, especially in Antarctica. The DMS maximum at MZS occurs in December, one month earlier than at other Antarctic stations. The maximum of DMS concentration is connected with the phytoplanktonic senescent phase following the bloom of Phaeocystis antarctica that occurs in the polynya when sea ice opens up. The second plankton bloom occurs in January and, despite the high dimethylsufoniopropionate (DMSP) concentration in seawater, atmospheric DMS remains low, probably due to its fast biological turnover in seawater in this period. The intensity and timing of the DMS evolution during the two years suggest that only the portion of the polynya close to the sampling site produces a discernible effect on the measured DMS. The closeness to the DMS source area and the occurrence of air masses containing DMS and freshly formed oxidation products allow us to study the kinetic of biogenic aerosol formation and the reliable derivation of the branch ratio between MSA and nssSO42- from DMS oxidation that is estimated to be 0.84±0.06. Conversely, for aged air masses with low DMS content, an enrichment of nssSO42- with respect to MSA, is observed. We estimate that the mean contribution of freshly formed biogenic aerosol to PM10 is 17 % with a maximum of 56 %. The high contribution of biogenic aerosol to the total PM10 mass in summer in this area highlights the dominant role of the polynya on biogenic aerosol formation. Finally, due to the regional and year-to-year variability of DMS and related biogenic aerosol formation, we stress the need for long-term measurements of seawater and atmospheric DMS and biogenic aerosol along the Antarctic coast and in the Southern Ocean.

Changes in aerosol particle composition during sea fog formation events in the sea ice regions of the Arctic Ocean

Water soluble ions (WSIs) of aerosol particles is one of the important parameters to study the aerosol-fog interactions. To study the changes of aerosol WSIs during sea fog events, hourly real-time measurements of WSIs (Na+, K+, Mg2+, Ca2+, MSA−, Cl−, NO3−, and SO42−) in total suspended aerosol particles (TSP) were conducted in the atmosphere over Arctic Ocean ice floe regions from August 1 to 12, 2017, when the sea fog events were frequently observed. There were significant differences in Na+, Cl−, Mg2+, methanesulfonic acid (MSA−), sea salt sulfate (ss-SO42) and non-sea salt sulfate (nss-SO42-) ions during sea fog events vs. non-sea fog periods. The mass concentrations of sea salt ions, such as Na+, Mg2+, Cl− and ss-SO42-, clearly increased before the occurrence of sea fog and then decreased substantially with the formation of sea fog; however, nss-SO42- levels did not decrease but remained high during the sea fog processes. These results suggest that sea salt aerosol particles were more likely to serve as condensation nuclei for fog and could be more effectively removed by sea fog than nss-SO42- particles. MSA− only combined with sea salt particles, which were likely to serve as condensation nuclei and be removed by sea fog. Condensation may be the primary factor leading to the reduction of sea salt ions during the sea fog periods, while other factors like the presence of dense sea ice and long-range transport input may also affect the decreasing rate.

Temporal variations in the chemical composition of aerosols over the coastal Bay of Bengal

Variations in source, ionic composition and carbonaceous components of aerosols are expected in the atmosphere due to reversing the direction of winds from winter to summer over the coastal Bay of Bengal (BoB). To examine this monthly, samples were collected at the weekly interval between March 2016 and February 2017 in the coastal BoB. The air mass back trajectories suggested that the study region received aerosols from Indo-Gangetic Plain from October to February whereas from central India during June to September and south or southwest during March to May. A higher concentration of total suspended particulate matter (TSP) was observed from November to February (winter) compared to other months. The concentration of sulphate contributed more than half of water-soluble inorganic species followed by sodium, ammonium and nitrate. The dominant contribution of anthropogenic SO42− (>90%) to total SO42− was observed. The ambient elemental carbon loadings and organic carbon to EC ratios indicate the dominant contribution of biomass burning emissions in the study region. The significant contribution of non-sea salt sulphate and nss-K+ indicates a dominant contribution from the continental sources throughout the year. The mass ratio of NO3−/anthropogenic SO42− suggests stationary sources (i.e., coal burning in power plants) contribute significantly over vehicular emissions during the entire study period. The mass balance of ionic composition suggests the acidic nature of aerosols. The estimated secondary aerosols accounted for ∼50% of organic carbon and 7% of TSP in the study region. This study has implications for understanding the source, composition and nature of aerosols and possible impacts on coastal water upon its deposition.

Biogenic aerosol in central East Antarctic Plateau as a proxy for the ocean-atmosphere interaction in the Southern Ocean

Ten years of data of biogenic aerosol (methane sulfonic acid, MSA, and non-sea salt sulfate, nssSO42−) collected at Concordia Station in the East Antarctic plateau (75° 06′ S, 123° 20′ E) are interpreted as a function of the Southern Annular Mode (SAM), Chlorophyll-a concentration (Chl-a; a proxy for phytoplankton biomass), sea ice extent and area. It is possible to draw three different scenarios that link these parameters in early, middle, and late summer. In early summer, the biogenic aerosol is significantly correlated to sea ice retreats through the phytoplankton biomass increases. Chl-a shows a significant correlation with nssSO42− in the finest fraction (< 1 μm). In contrast, only Chl-a in West Pacific and Indian Ocean sectors correlates with MSA in the coarse fraction. The transport routes towards the inner Antarctic plateau and aerosol formation processes could explain the different correlation patterns of the two compounds both resulting from the DMS oxidation. In mid-summer, Chl-a concentrations are at the maximum and are not related to sea ice melting. Due to the complexity of transport processes of air masses towards the Antarctic plateau, the MSA concentrations are low and not related to Chl-a concentration. In late summer, MSA and nssSO42− present the highest concentrations in their submicrometric aerosol fraction, and both are significantly correlated with Chl-a but not with the sea ice. In early and mid-summer, the enhanced efficiency of transport processes from all the surrounding oceanic sectors with air masses traveling at low elevation can explain the highest concentrations of nssSO42− and especially MSA. Finally, considering the entire time series, MSA shows significant year-to-year variability. This variability is significantly correlated with SAM but with a different time lag in early (0-month lag) and late summer (4-months lag). This correlation likely occurs through the effect of the SAM on phytoplankton blooms.

Transboundary air pollution reduction rapidly reflected in stream water chemistry in forested catchment on the sea of Japan coast in central Japan

Since the 1980s, Japan has been affected by transboundary air pollution from the Asian continent due to northwesterly seasonal winds in the winter. However, after peaks in 2006 and 2011/2012, sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions began decreasing, respectively. To assess the biogeochemical response of forest ecosystems to the changing atmospheric deposition, flux observations of rainfall outside forest canopies (RF), throughfall and stemflow (TF + SF), and stream water (SW) chemistry were conducted in a Japanese cedar plantation in Kajikawa (KJK) on the Sea of Japan coast in central Japan. Fluxes of S and N by RF and TF + SF at KJK significantly decreased during the observation period (2002–2018). The non-sea salt sulfate (SO42−) flux by TF + SF peaked in 2006/2007 and decreased thereafter, which likely reflected the S emission trends. Accordingly, SO42− concentrations in SW at KJK decreased with increasing alkalinity. Similar decreases in SO42− concentrations beginning in 2006, 2007, and 2008 were observed at eight monitoring lakes in Japan. Thus, the SW chemistry at KJK and possibly that of Japanese lakes were sensitive to atmospheric S deposition reductions. However, as of late, the net S export at KJK has been increasing, exhibiting budget discrepancies in 2014/2015 and 2017/2018. Sulfur isotopic analysis suggested that the S deposited from the atmosphere was retained/cycled in the forest before it was gradually discharged into SW. Thus, a slightly weakened reaction of the output due to the internal cycle and residual effects of previous years may have caused the S budget discrepancies. The nitrate (NO3−) concentration in the SW at KJK has also been continuously increasing. N deposition and other factors, such as the maturation of the planted trees, may play an important role in NO3− leaching in plantations.

Atmospheric deposition across the Atacama Desert, Chile: Compositions, source distributions, and interannual comparisons

Hyper-arid areas such as the Atacama Desert accumulated significant amounts of insoluble dust and soluble salts from the atmosphere, providing minable salt deposits as well as mimicking the surface processes on Mars. The deposition rates, compositions and sources, however, were poorly constrained. Especially, the variabilities of atmospheric deposition in the Atacama Desert corresponding to a changing climate were unassessed. In this work, the atmospheric depositions collected using dust traps across a west-east elevation gradient in the Atacama (~23°S) from 1/2/2010 to 12/31/2011 were analyzed and compared to previous results in 2007–2009. The insoluble dust deposition rates in our sampling period were significantly higher than those of 2007–2009 in most dust traps, which was attributed to the changes in wind, highlighting the importance of long-term monitoring of insoluble dust fluxes. Soluble salts, instead, showed less distinct interannual variations in deposition rates, geochemical compositions or source contributions. At the coastal site (T1), soluble salts were originated from both primary sea-salt (SS) aerosols and non-sea-salt (NSS) sources such as anthropogenic emission, marine biogenic emission and biomass burning; the deposition rates of these salts largely depended on the wind speed and the amount of anthropogenic emissions. Sulfur isotopic evidence further showed that NSS sulfate at T1 was mainly originated from local SO2 emission from local power plants. The inland sites (T2-T8) displayed much lower soluble salts deposition rates, and the salts were primarily sourced from entrainment of local surface minerals, including Na(Cl, NO3), CaSO4, and nitrate formed via atmospheric oxidation of anthropogenic NOx. Sulfur isotopic compositions of sulfate deposited at T2-T8 were similar to those in local surface soil; however, three sites near the Chuquicamata mine showed slightly lower δ34Ssulfate values, indicating the presence of secondary sulfate originated from mining activities. The soluble salts deposited at the Andean site (T10) were dominantly from wet deposition that incorporated local lake salts, and therefore, the deposition rates were mainly controlled by the amount of precipitation.

Stable carbon and nitrogen isotope compositions of bulk aerosol samples over the South China Sea

The marine aerosols is mainly produced primary sea salt and secondary form of non-sea salt (nss) sulfate and organic species from marine emission, but get modified significantly by the anthropogenic and terrestrial materials, such as total carbon (TC) and total nitrogen (TN), which transported by the atmospheric circulation from land to the ocean. Rarely studies focus on the TC and TN in marine aerosol in the open ocean due to the sampling difficulty, let alone the annual observation. Concentrations of TC and TN, and their isotope compositions (δ13C-TC and δ15N-TN) were measured in total suspended particulate (TSP) which sampled at Yongxing Island over the South China Sea from March 2014 to February 2015, and coastal mega-city Guangzhou in April/May and October/November 2014. The annual average concentrations of TC and TN at Yongxing Island were 4.20 ± 2.38 μg m−3 and 0.77 ± 0.47 μg m−3, respectively. Much higher concentration of TC and TN were observed at Guangzhou. Contributions of NO3− and NH4+ (inorganic nitrogen, IN) to TN at Yongxing Island averaged 55.7% and 6.8%, respectively, while they averaged 27.4% and 12.2% at Guangzhou, respectively. The average values of δ15N in TN were +0.7 ± 3.3‰, +6.8 ± 6.3‰ and −0.7 ± 2.7‰ during winter, transitional and warm seasons, respectively, with an annual average value of +1.1 ± 4.3‰. The δ13C of TC varied from −16.2 to −26.8‰, with an annual average value of −22.7‰. The average of values of δ13C were −22.9 ± 1.7‰, −22.9 ± 1.4‰, and −22.4 ± 2.6‰ during winter, transitional and warm seasons, respectively. The average values of δ15N in TN and δ13C of TC were +13.2 ± 0.9‰ and −25.8 ± 0.4‰ in winter season, +13.6 ± 0.8‰ and - 26.5 ± 0.3‰ in warm season at Guangzhou, respectively. Based on aerosol δ15N and δ13C values, the marine realm may be an important source of aerosol TN, while aerosol TC may dominantly contributed by the combustion of fossil fuels and biomass burning from continental mass over the South China Sea. The secondary aerosol formation and long-range transport on aerosol chemistry also varied the concentrations and isotopic composition of TN and TC at Yongxing Island.

Biogenic hydrogen sulphide emissions and non-sea sulfate aerosols over the Indian Sundarban mangrove forest

Temporal variations in atmospheric hydrogen sulphide concentrations and its biosphere-atmosphere exchanges were studied in the World’s largest mangrove ecosystem, Sundarbans, India. The results were used to understand the possible contribution of H2S fluxes in the formation of atmospheric aerosol of different size classes (e.g. accumulation, nucleation and coarse mode). The mixing ratio of hydrogen sulphide (H2S) over the Sundarban mangrove atmosphere was found maximum during the post-monsoon season (October to January) with a mean value of 0.59 ± 0.02 ppb and the minimum during pre-monsoon (February to May) with a mean value of 0.26 ± 0.01 ppb. This forest acted as a perennial source of H2S and the sediment-air emission flux ranged between 1213 ± 276 μg S m−2 d−1(December) and 457 ± 114 μg S m−2 d−1 (August) with an annual mean of 768 ± 240 μg S m−2d−1. The total annual emissions of H2S from the Indian Sundarban were estimated to be 1.2 ± 0.6 Tg S. The accumulation mode of aerosols was found to be more enriched with non-sea salt sulfate with an average loading of 5.74 μg m−3 followed by the coarse mode (5.18 μg m−3) and nucleation mode (1.18 μg m−3). However, the relative contribution of Non-sea salt sulfate aerosol to total sulfate aerosol was highest in the nucleation mode (83%) followed by the accumulation (73%) and coarse mode (58%). Significant positive relations between H2S flux and different modes of NSS indicated the likely link between H2S, a dominant precursor for the non-sea salt sulfate, and non-sea sulfate aerosol particles. An increase in H2S emissions from the mangrove could result in an increase in enhanced NSS in aerosol and associated cloud albedo, and a decrease in the amount of incoming solar radiation reaching the Sundarban mangrove forest.

Effect of seasonal mesoscale and microscale meteorological conditions in Ny-Ålesund on results of monitoring of long-range transported pollution

ABSTRACTNy-Alesund is an international research settlement where the thermodynamics and chemical composition of the air are monitored. The present work investigates the effects of micrometeorological conditions, mesoscale dynamics and local air pollution on the data collected at two different locations around the village. Daily filter measurements of sulphur dioxide and non-sea salt sulphate from the temporary Ny-Alesund station and permanent Zeppelin mountain station have been analysed along with meteorological data. The influence of different factors representing micrometeorological phenomena and local pollution from ships has been statistically investigated. Seasonal variation of the correlation between the data from Ny-Alesund and Zeppelin stations is revealed, and the seasonal dependence of the relative contribution of different factors has been analysed. The median concentrations of SO42- measured in Ny-Alesund increased significantly on days with temperature inversions in winter. In spring, concent...

Characterization of PM2.5 and identification of transported secondary and biomass burning contribution in Seoul, Korea.

The chemical and seasonal characteristics of fine particulates in Seoul, Korea, were investigated based on 24-h integrated PM2.5 measurements made over four 1-month periods in each season between October 2012 and September 2013. The four-season average concentration of PM2.5 was 37μgm-3, and the major chemical components were secondary inorganic aerosol (SIA) species of sulfate, nitrate, and ammonium (49%), followed by organic matter (34%). The mass concentration and most of the chemical components of PM2.5 showed clear seasonal variation, with a winter-high and summer-low pattern. The winter-to-summer sulfate ratio and the winter organic carbon (OC)-to-elemental carbon (EC) ratio were unusually high compared with those in previous studies. Strong correlations of both the sulfate level and the sulfur oxidation ratio with relative humidity, and between water-soluble OC (WSOC) and SIA in winter, suggest the importance of aqueous phase chemistry for secondary aerosols. A strong correlation between non-sea salt sulfate and Na+ levels, a high Cl-/Na+ ratio, and an unusual positive correlation between the nitrogen oxidation ratio and temperature during the winter indicate the influence of transported secondary emission sources from upwind urban areas and from China across the Yellow Sea. Despite the absence of local forest fires and the regulation of wood burning, a high levoglucosan concentration and its correlations with OC and WSOC indicate that Seoul was affected by biomass burning sources in the winter. The unusually high water-insoluble OC (WIOC)-to-EC ratio in winter implies additional transported combustion sources of WIOC. The strong correlation between WIOC and levoglucosan suggests the likely influence of transported biomass burning sources on the high WIOC/EC ratio during the winter.

Seasonal trends, chemical speciation and source apportionment of fine PM in Tehran

Frequent air pollution episodes have been reported for Tehran, Iran, mainly because of critically high levels of fine particulate matter (PM2.5). The composition and sources of these particles are poorly known, so this study aims to identify the major components and heavy metals in PM2.5 along with their seasonal trends and associated sources. 24-hour PM2.5 samples were collected at a main residential station every 6 days for a full year from February 2014 to February 2015. The samples were analyzed for ions, organic carbon (including water-soluble and insoluble portions), elemental carbon (EC), and all detectable elements. The dominant mass components, which were determined by means of chemical mass closure, were organic matter (35%), dust (25%), non-sea salt sulfate (11%), EC (9%), ammonium (5%), and nitrate (2%). Organic matter and EC together comprised 44% of fine PM on average (increased to >70% in the colder season), which reflects the significance of anthropogenic urban sources (i.e. vehicles). The contributions of different components varied considerably throughout the year, particularly the dust component that varied from 7% in the cold season to 56% in the hot and dry season. Principal component analyses were applied, resulting in 5 major source factors that explained 85% of the variance in fine PM. Factor 1, representing soil dust, explained 53%; Factor 2 denotes heavy metals mainly found in industrial sources and accounted for 18%; and rest of factors, mainly representing combustion sources, explained 14% of the variation. The levels of major heavy metals were further evaluated, and their trends showed considerable increases during cold seasons. The results of this study provide useful insight to fine PM in Tehran, which could help in identifying their health effects and sources, and also adopting effective control strategies.

An advanced modeling study on the impacts and atmospheric implications of multiphase dimethyl sulfide chemistry

Oceans dominate emissions of dimethyl sulfide (DMS), the major natural sulfur source. DMS is important for the formation of non-sea salt sulfate (nss-SO42-) aerosols and secondary particulate matter over oceans and thus, significantly influence global climate. The mechanism of DMS oxidation has accordingly been investigated in several different model studies in the past. However, these studies had restricted oxidation mechanisms that mostly underrepresented important aqueous-phase chemical processes. These neglected but highly effective processes strongly impact direct product yields of DMS oxidation, thereby affecting the climatic influence of aerosols. To address these shortfalls, an extensive multiphase DMS chemistry mechanism, the Chemical Aqueous Phase Radical Mechanism DMS Module 1.0, was developed and used in detailed model investigations of multiphase DMS chemistry in the marine boundary layer. The performed model studies confirmed the importance of aqueous-phase chemistry for the fate of DMS and its oxidation products. Aqueous-phase processes significantly reduce the yield of sulfur dioxide and increase that of methyl sulfonic acid (MSA), which is needed to close the gap between modeled and measured MSA concentrations. Finally, the simulations imply that multiphase DMS oxidation produces equal amounts of MSA and sulfate, a result that has significant implications for nss-SO42- aerosol formation, cloud condensation nuclei concentration, and cloud albedo over oceans. Our findings show the deficiencies of parameterizations currently used in higher-scale models, which only treat gas-phase chemistry. Overall, this study shows that treatment of DMS chemistry in both gas and aqueous phases is essential to improve the accuracy of model predictions.

Sulfate source apportionment in the Ny-Ålesund (Svalbard Islands) Arctic aerosol

Daily PM10 aerosol samples were collected at the Gruvebadet observatory, Ny-Alesund (Svalbard Islands), during the spring-summer 2014 Italian Arctic Campaign. A total of 136 samples were analysed for ion (inorganic anions and cations, selected organic anions) composition aiming to evaluate the seasonal pattern of sulfate, as a key component of the Arctic haze. Ionic balances indicated a strong sulfate seasonality with mean spring concentration about 1.5 times higher than that measured in summer. The spring and summer aerosol was almost neutral, indicating that ammonia was the major neutralizing agent for atmospheric acidic species. The linear regression between sulfate from potential acidic sources (non-sea salt sulfate and non-crustal sulfate) and ammonium indicated that the mean sulfate/ammonium ratio was intermediate between semi-(NH4HSO4) and complete ((NH4)2SO4) neutralization. Using sea-salt sodium as sea-spray marker, non-sea-salt calcium as crustal marker and methanesulfonic acid as biogenic marker, a detailed source apportionment for sulfate was carried out. The anthropogenic input (calculated as the differences between total sulfate and the sum of sea-salt, crustal and biogenic contributes) was found to be the most relevant contribution to the sulfate budget in the Ny-Alesund aerosol in summer and, especially, in spring. In this last season, crustal, sea-salt, biogenic and anthropogenic sources accounted for 3.3, 12.0, 11.5 and 74.8 %, respectively.

Scavenging of black carbon in Chilean coastal fogs

In November/December 2013 a pilot experiment on aerosol/fog interaction was conducted on a coastal hill in the suburbs of Valparaíso, Chile. Passages of garúa fog were monitored with continuous recordings of a soot photometer and an optical aerosol spectrometer. An optical fog sensor and an automatic weather station provided meteorological data with which the aerosol could be classified. High-resolution back trajectories added meteorological information. From filter samples, optical and chemical aerosol information was derived. Scavenging coefficients of black carbon (BC) and measured particulate mass below 1μm diameter (PM1) were estimated with three approaches. Averaging over all fog periods of the campaign yielded a scavenging coefficient of only 6% for BC and 40% for PM1. Dividing the data into four 90°-wind sectors gave scavenging factors for BC ranging from 13% over the Valparaíso, Viña del Mar conurbation to 50% in the marine sector (180°–270°). The third, and independent approach was achieved with two pairs of chemical aerosol samples taken inside and outside fogs, which yielded a scavenging coefficient of 25% for BC and 70% for nonseasalt sulfate. Whereas fogs occurred rather infrequently in the beginning of the campaign highly regular daily fog cycles appeared towards the end of the experiment, which allowed the calculation of typical diurnal cycles of the aerosol in relation to a fog passage.