Water-soluble Organic Carbon Concentrations Research Articles

Long-term characterization of organic and elemental carbon in the PM<sub>2.5</sub> fraction: the case of Athens, Greece

Abstract. Organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and main ions were measured in a total of 1510 PM2.5 daily aerosol samples collected from May 2008 to April 2013 in Athens, Greece. OC and EC concentrations were 2.1 ± 1.3 μg m−3 and 0.54 ± 0.39 μg m−3, accounting for 11 ± 3% and 3 ± 1% of PM2.5 mass, respectively, with an average OC/EC ratio of 4.7 ± 3.1. Significant correlation was found between OC and EC during the whole period, indicating emissions by common primary sources on a regional scale. WSOC concentration ranged from 0.03 to 10.6 μg m−3, with an average of 1.5 ± 0.9 μg m−3. By considering the Finokalia (Crete) station as a reference, it was estimated that, during the warm season in Athens, 67 ± 7% of emitted OC and 53 ± 12% of emitted EC is regional, while, during cold months, the regional contribution of OC is only 33 ± 7% and of EC 29 ± 8%. Furthermore, secondary organic carbon (SOC) was calculated for the warm period of the year (April to October). The estimated SOC constituted about 75 ± 6% of PM2.5 organic carbon in Athens, highlighting significant aging processes on a regional scale. In the period 2011–2013 and during wintertime, an increase in OC and EC levels was observed, attributed to an increase in wood burning for domestic heating due to the economic crisis.

Physicochemical characteristics, oxidative capacities and cytotoxicities of sulfate-coated, 1,4-NQ-coated and ozone-aged black carbon particles

Black carbon (BC) particles play important roles in climate change, visibility impairment, atmospheric reaction process, and health effect. The aging processes of BC alter not only atmospheric composition, but also the physicochemical characteristics of BC itself, thus impacting the environment and health effects. Here, three types of BC including sulfate-coated, 1,4-naphthoquinone (1,4-NQ)-coated, and O3-aged BC are presented. The morphologies, structures, extraction components, the amount of water-soluble organic carbon (WSOC) and free radical intensities of the three types of BC particles are examined by transmission electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), ultraviolet–visible spectrophotometry, total organic carbon detector and electron paramagnetic resonance, respectively. Dithiothreitol (DTT) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide assays are utilized to assess the changes in oxidative capacity and cytotoxicity towards murine alveolar macrophage cells. The orders of DTT activities and cytotoxicities of the particles are both arranged as follows: BC/1,4-NQ>BC/O3>BC>BC/sulfate, mainly because 1,4-NQ owned high oxidative potential and cytotoxicity, while sulfate did not exhibit oxidative capacity and cytotoxicity. The insoluble components of particles contribute most of the total DTT activity, whereas either water or methanol extract is minor contributor. DTT activity was positively correlated with both WSOC content and free radical intensity, with the correlation between DTT activity and WSOC content was stronger than that between DTT activity and free radical intensity.

Soil carbon and nitrogen in the active layers of the permafrost regions in the Three Rivers’ Headstream

The pedogenesis, soil organic carbon (SOC), soil inorganic carbon (SIC), hot water-soluble organic carbon (WSOC) and total nitrogen (TN) of the active layers were examined beneath four typical vegetation communities in the permafrost regions in the Three Rivers’ Headstream region in the Qinghai-Tibetan Plateau. In all soil areas, except for in the steppe, the SOC and TN showed rapidly decreasing trends with increasing depth. The highest SOC, WSOC and TN contents were found in the wet meadow, with contents in the eluviate layer being 180.9, 40.2 and 10.9 g kg−1, respectively. In the steppe, the average SOC, WSOC and TN at 180 cm depth were 6.2, 0.67 and 0.59 g kg−1, respectively. The SIC contents showed increasing trends with increasing depth in the soils of the steppe community. The correlation analysis suggested that the moisture and fine particle fractions positively correlated to SOC, TN and WSOC, while bulk density and pH negatively correlated to SOC, TN and WSOC. The SOC and TN were significantly related to bulk density. The SIC was positively correlated with pH but negatively correlated with SOC, TN and WSOC. The C/N ratios were negatively correlated with pH while positively correlated with SOC, TN and fine soil particles. The results suggest that the SOC in the wet meadow soils in the permafrost regions of Qinghai-Tibetan have the largest potential contributions to the emissions of greenhouse gases and cause future global warming.

Can δ13C abundance, water-soluble carbon, and light fraction carbon be potential indicators of soil organic carbon dynamics in Zoigê wetland?

Zoigê alpine wetland located at the Qinghai–Tibet Plateau, China, is the largest alpine wetland in the world and very sensitive to global climate changes. However, little is known of the dynamics of soil water soluble organic carbon (WSOC), light fraction organic carbon (LFOC), soil organic carbon (SOC) and its indicators in this alpine wetland. In this study, four wetland sites and one degraded wetland site in the Zoigê alpine wetland were selected to investigate the relationships of stable isotope and labile organic carbon dynamics with groundwater elevation or water table level. We also examine if the δ13C abundance, WSOC, and LFOC can be used as potential indicators of SOC dynamics in these wetland sites. The results showed that the plant dominant species in the degraded wetland site were different from those in the non-degraded wetland sites. Moreover, the declining water table did not significantly lower foliar δ13C, C and N concentrations and C/N ratio of dominant plant species, but led to a significant decrease of soil SOC, WSOC and LFOC concentrations and an increase of soil δ13C. In the wetland sites, SOC was significantly correlated with soil δ13C, WSOC, and LFOC. Our regression analysis showed that LFOC was the best potential indicator of SOC dynamics with WSOC and soil δ13C being less useful as indicators, respectively. In addition, the absolute slope coefficients of the regression models increased as the soil depth increased, which indicated that the SOC turnover increased with soil depth.

Brown carbon in atmospheric outflow from the Indo-Gangetic Plain: Mass absorption efficiency and temporal variability

The simultaneous measurements of brown carbon (BrC) and elemental carbon (EC) are made in ambient aerosols (PM2.5), collected from a site in north-east India during November'09–March'10, representing the atmospheric outflow from the Indo-Gangetic Plain (IGP) to the Bay of Bengal (BoB). The absorption coefficient of BrC (babs), assessed from water-soluble organic carbon (WSOC) at 365 nm, varies from 2 to 21 M m−1 and exhibits significant linear relationship (P < 0.05) with WSOC concentration (3–29 μg m−3). The angstrom exponent (α: 8.3 ± 2.6, where babs ≈ λ−α.) is consistent with that reported for humic-like substances (HULIS) from biomass burning emissions (BBE). The impact of BBE is also discernible from mass ratios of nss-K+/EC (0.2–1.4) and OC/EC (3.4–11.5). The mass fraction of WSOC (10–23%) in PM2.5 and mass absorption efficiency of BrC (σabs-BrC: 0.5–1.2 m2 g−1) bring to focus the significance of brown carbon in atmospheric radiative forcing due to anthropogenic aerosols over the Indo-Gangetic Plain.

Effect of Vegetation Succession on Organic Carbon, Carbon of Humus Acids and Dissolved Organic Carbon in Soils of Copper Mine Tailings Sites

Carbon of humus acids (HSAC) and dissolved organic carbon (DOC) are the most active forms of soil organic carbon (SOC) and play an important role in global carbon recycling. We investigated the concentrations of HSAC, water-soluble organic carbon (WSOC), hot water-extractable organic carbon (HWOC) and SOC in soils under different vegetation types of four copper mine tailings sites with differing vegetation succession time periods in Tongling, China. The concentrations of HSAC, WSOC, HWOC and SOC increased with vegetation succession. WSOC concentration increased with the accumulation of SOC in the tailings, and a linearly positive correlation existed between the concentrations of HSAC and SOC in the tailings. However, the percentages of HSAC and DOC in the SOC decreased during vegetation succession. The rate of SOC accumulation was higher when the succession time was longer than 20 years, whereas the speeds of soil organic matter (SOM) decomposition and humification were slow, and the concentrations of HSAC and DOC increased slowly in the tailings. The percentage of carbon of humic acid (HAC) in HSAC increased with vegetation succession, and the values of humification index (HI), HAC/carbon of fulvic acid, also increased with the accumulation of HSAC and SOC in soils of the tailings sites. However, the HI value in the each of the tailings was less than 0.50. The humification rate of SOM was lower than the accumulation rate of SOM, and the level of soil fertility was still very low in the tailings even after 40 years of natural restoration.

One-year observations of carbonaceous and nitrogenous components and major ions in the aerosols from subtropical Okinawa Island, an outflow region of Asian dusts

Abstract. Ambient aerosol samples (TSP, n = 50) were collected for 12 months at subtropical Okinawa Island, Japan, an outflow region of Asian dusts in the western North Pacific and analysed for organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), water-soluble total nitrogen (WSTN), water-soluble organic nitrogen (WSON) and major ions to better understand the formation and transformation of East Asian aerosols during long-range atmospheric transport. Concentration ranges of these components are; OC: 0.76–7.1 μg m−3 (av. 1.7 ± 1.0 μg m−3), EC: 0.07–0.96 μg m−3 (0.28 ± 0.19 μg m−3), WSOC: 0.27–1.9 μg m−3 (0.73 ± 0.38 μg m−3), WSTN: 0.77 to 3.0 μg m−3 (0.58 ± 0.46 μg m−3) and WSON: 0.0–2.2 μg m−3 (0.12 ± 0.23 μg m−3). Higher OC concentrations were obtained in active biota seasons; spring (av. 2.4 μg m−3) and summer (1.8 μg m−3). EC and WSOC concentrations maximized in spring (av. 0.41 μg m−3 and 0.95 μg m−3, respectively) followed by winter (0. 70 and 0.90 μg m−3) whereas they became lowest in summer (0.19 and 0.52 μg m−3). In contrast, WSTN concentrations were highest in winter (0.86 μg m−3) and lowest in summer (0.37 μg m−3) and autumn (0.34 μg m−3). Concentrations of WSON are higher in early summer (av. 0.26 μg m−3) due to the emission from marine biota. The high ratios of OC / EC (av. 7.6) and WSOC / OC (44%) suggest a secondary formation of organic aerosols. Strong correlation between OC and MSA- (0.81) in spring suggests that springtime aerosols are influenced by additional marine and terrestrial biogenic sources. The positive correlation of Ca2+ and TSP in spring (r = = 0.81) demonstrates a significant contribution of Asian dust whereas high abundances of NO3- and nss-SO42- in winter suggest an important contribution from anthropogenic sources including biomass burning, vehicular emission and coal combustion. NH4-N/WSTN ratios peaked in winter (0.56), indicating a significant contribution of biomass burning to WSTN in cold season. In contrast, higher NO3-N/WSTN ratio in spring than winter suggests that the atmospheric transport of vehicular emissions maximizes in spring. Correlation analyses of major ions suggest that NH4+ and Ca2+ play major role in the neutralization of acidic aerosols forming NH4HSO4, (NH4)2SO4 and CaSO4.

Functional characterization of the water-soluble organic carbon of size-fractionated aerosol in the southern Mississippi Valley

The chemical content of water-soluble organic carbon (WSOC) as a function of particle size was characterized in Little Rock, Arkansas in winter and spring 2013. The objectives of this study were to (i) compare the functional characteristics of coarse, fine and ultrafine WSOC and (ii) reconcile the sources of WSOC for periods when carbonaceous aerosol was the most abundant particulate component. The WSOC accounted for 5 % of particle mass for particles with δp > 0.96 μm and 10 % of particle mass for particles with δp < 0.96 μm. Non-exchangeable aliphatic (H–C), unsaturated aliphatic (H–C–C=), oxygenated saturated aliphatic (H–C–O), acetalic (O–CH–O) and aromatic (Ar–H) protons were determined by proton nuclear magnetic resonance (1H-NMR). The total non-exchangeable organic hydrogen concentrations varied from 4.1 ± 0.1 nmol m−3 for particles with 1.5 < δp < 3.0 μm to 73.9 ± 12.3 nmol m−3 for particles with δp < 0.49 μm. The molar H/C ratios varied from 0.48 ± 0.05 to 0.92 ± 0.09, which were comparable to those observed for combustion-related organic aerosol. The R–H was the most abundant group, representing about 45 % of measured total non-exchangeable organic hydrogen concentrations, followed by H–C–O (27 %) and H–C–C= (26 %). Levoglucosan, amines, ammonium and methanesulfonate were identified in NMR fingerprints of fine particles. Sucrose, fructose, glucose, formate and acetate were associated with coarse particles. These qualitative differences of 1H-NMR profiles for different particle sizes indicated the possible contribution of biological aerosols and a mixture of aliphatic and oxygenated compounds from biomass burning and traffic exhausts. The concurrent presence of ammonium and amines also suggested the presence of ammonium/aminium nitrate and sulfate secondary aerosol. The size-dependent origin of WSOC was further corroborated by the increasing δ13C abundance from −26.81 ± 0.18 ‰ for the smallest particles to −25.93 ± 0.31 ‰ for the largest particles and the relative distribution of the functional groups as compared to those previously observed for marine, biomass burning and secondary organic aerosol. The latter also allowed for the differentiation of urban combustion-related aerosol and biological particles. The five types of organic hydrogen accounted for the majority of WSOC for particles with δp > 3.0 μm and δp < 0.96 μm.

Seasonal variations of anhydrosugars in PM2.5 in the Pearl River Delta Region, China

Anhydrosugars including levoglucosan and mannosan are the most effective organic tracers for biomass burning aerosol in the atmosphere. In this study, to investigate the contribution of biomass burning emissions to the aerosol burden in the Pearl River Delta (PRD) region, China, 24-hour integrated PM2.5 samples were collected simultaneously at four locations, (i) Guangzhou (GZ), (ii) Zhaoqing (ZQ) in Guangdong province, (iii) Hok Tsui (HT) and (iv) Hong Kong Polytechnic University (PU) in Hong Kong, in four seasons between 2006 and 2007. Levoglucosan and mannosan, together with water-soluble inorganic ions and water-soluble organic carbon (WSOC), were determined to elucidate the seasonal and spatial variations in biomass burning contributions. The concentrations of levoglucosan and mannosan were on average 82.4±123 and 5.8±8.6 ng m−3, respectively. The WSOC concentrations ranged from 0.2 to 9.4 µg m−3, with an average of 2.1±1.6 µg m−3. The relative contributions of biomass burning emissions to OC were 33% in QZ, 12% in GZ, 4% at PU and 5% at HT, respectively, estimated by the measured levoglucosan to organic carbon ratio (LG/OC) relative to literature-derived LG/OC values. The contributions from biomass burning emissions were in general 1.7–2.8 times higher in winter than those in other seasons. Further, it was inferred from diagnostic tracer ratios that a significant fraction of biomass burning emissions was derived from burning of hard wood and likely also from field burning of agricultural residues, such as rice straw, in the PRD region. Our results highlight the contributions from biomass/biofuel burning activities on the regional aerosol budget in South China.

Characterization of biochar-derived dissolved organic matter using UV–visible absorption and excitation–emission fluorescence spectroscopies

In recent years, biochar has become of considerable interest for a variety of environmental applications. However, the feasibility of its application is entirely dependent on its physical and chemical properties, including the characteristics of biochar-derived dissolved organic matter (DOM). The goal of this study was to assess the use of optical analysis for the purpose of characterizing biochar-derived DOM. Three different biochars (slow pyrolysis birch and maple; fast pyrolysis maple) were produced and leached in distilled water over 17d. Samples were taken on days 3, 10, 13 and 17, filtered, and analyzed for DOC content. Samples were also subjected to optical analysis using UV–visible absorption and excitation–emission matrix (EEM) fluorescence spectroscopies. EEM fluorescence data were further analyzed using parallel factor analysis (PARAFAC). Absorbance and fluorescence results were combined and examined using principal component analysis (PCA). Significant differences in the water soluble organic carbon content were observed for all biochar types. The estimated aromaticity (SUVA254) and mean molecular weight (S275–295) of biochar-derived DOM were also found to differ based on biochar type. PARAFAC analysis identified three humic-like components and one protein-like component. Distinct DOM signatures were observed for each biochar type. Transformations in biochar DOM characteristics over time were also observed. The PCA showed a clear delineation in biochar types based on their optical properties. The results of this study indicate that optical analysis may provide valuable information regarding the characteristics of biochar-derived DOM.

Light absorbing organic aerosols (brown carbon) over the tropical Indian Ocean: impact of biomass burning emissions

The first field measurements of light absorbing water-soluble organic carbon (WSOC), referred as brown carbon (BrC), have been made in the marine atmospheric boundary layer (MABL) during the continental outflow to the Bay of Bengal (BoB) and the Arabian Sea (ARS). The absorption signal measured at 365 nm in aqueous extracts of aerosols shows a systematic linear increase with WSOC concentration, suggesting a significant contribution from BrC to the absorption properties of organic aerosols. The mass absorption coefficient (babs) of BrC shows an inverse hyperbolic relation with wavelength (from ∼300 to 700 nm), providing an estimate of the Angstrom exponent (αP, range: 3–19; Av: 9 ± 3). The mass absorption efficiency of brown carbon (σabs−BrC) in the MABL varies from 0.17 to 0.72 m2 g−1 (Av: 0.45 ± 0.14 m2 g−1). The αP and σabs−BrC over the BoB are quite similar to that studied from a sampling site in the Indo-Gangetic Plain (IGP), suggesting the dominant impact of organic aerosols associated with the continental outflow. A comparison of the mass absorption efficiency of BrC and elemental carbon (EC) brings to focus the significant role of light absorbing organic aerosols (from biomass burning emissions) in atmospheric radiative forcing over oceanic regions located downwind of the pollution sources.

Labile organic matter content and distribution as affected by six-year soil amendments to eroded Chinese mollisols

Labile organic carbon (LOC) is a fraction of soil organic carbon (SOC) with rapid turnover time and is affected by soil fertilization. This investigation characterized the SOC content, LOC content and LOC distribution in the treatment plots of surface soil erosion at five levels (0-, 5-, 10-, 20- and 30-cm erosion). The soil had received contrasting fertilizer treatments (i.e., chemical fertilizer or chemical fertilizer + manure) for 6 years. This study demonstrated that both SOC and various LOC fractions contents were higher in the plots with fertilizer + manure than in those with fertilizer alone under the same erosion conditions. The SOC and LOC contents decreased as the erosion depth increased. Light fraction organic carbon, particulate organic carbon, easily oxidizable organic carbon (KMnO4-oxydizable organic carbon), and microbial biomass carbon were 27%–57%, 37%–47%, 20%–25%, and 29%–33% higher respectively in the fertilizer + manure plots, than in the fertilizer alone plots. Positive correlations (p < 0.05) between SOC content and different fractions contents were observed in all plots except the correlation between total SOC content and water-soluble organic carbon content in the different fertilization treatments. Obviously, fertilizer + manure treatments would be conducive to the accumulation of LOC and SOC in the Black soil of Northeast China.

Changes in Droplet Surface Tension Affect the Observed Hygroscopicity of Photochemically Aged Biomass Burning Aerosol

This study examines the hygroscopic and surface tension properties as a function of photochemical aging of the aerosol emissions from biomass burning. Experiments were conducted in a chamber setting at the UC-Riverside Center for Environmental Research and Technology (CE-CERT) Atmospheric Processes Lab using two biomass fuel sources, manzanita and chamise. Cloud condensation nuclei (CCN) measurements and off-line filter sample analysis were conducted. The water-soluble organic carbon content and surface tension of the extracted filter samples were measured. Surface tension information was then examined with Köhler theory analysis to calculate the hygroscopicity parameter, κ. Laboratory measurement of biomass burning smoke from two chaparral fuels is shown to depress the surface tension of water by 30% or more at organic matter concentrations relevant at droplet activation. Accounting for surface tension depression can lower the calculated κ by a factor of 2. This work provides evidence for surface tension depression in an important aerosol system and may provide closure for differing sub- and supersaturated κ measurements.

Investigation of the sources and seasonal variations of secondary organic aerosols in PM2.5 in Shanghai with organic tracers

One hundred and forty seasonal PM2.5 samples were collected from January 2010 to January 2011 at one urban site and one suburban site simultaneously in a Chinese megacity, Shanghai, to study the concentrations and seasonal variation of secondary organic aerosols (SOA). Concentrations of water-soluble organic carbon (WSOC) were determined together with organic and elemental carbons. Thirteen organic tracers, including the tracer for biomass burning and tracers for SOA from isoprene, α-pinene, β-caryophyllene and toluene, were measured. EC-based method, WSOC-based method, tracer-based method and PMF modeling were used to estimate the seasonal contributions of secondary organic carbon (SOC) in Shanghai, and the results from the different methods were compared and evaluated. Biomass burning was the major contributor to the measured WSOC in the autumn sampling period, while SOA was the major contributor in the other seasons. The concentrations of the SOA tracers in summer were obviously higher than that in other seasons. It was found that SOC estimated with the tracer-based method accounted for only a small part of the SOC from the WSOC-based method in Shanghai, especially for the winter and spring sampling periods. PMF results showed that a large part of the SOC was associated with sulfate and nitrate but not with the SOA tracers.

Behavior of MCPA in four intensive cropping soils amended with fresh, composted, and aged olive mill waste

An evaluation was made of the impact of olive mill waste and its organic matter transformation on the sorption, desorption, leaching, and degradation of the herbicide MCPA when the waste was applied to four Mediterranean soils. The soils were amended in the laboratory with fresh, composted, and field-aged olive mill waste (OW, COW, and AOW treatments, respectively). It was found that the greater the amount of OW applied to the soils, but especially the greater its organic matter maturity, the greater the adsorption of MCPA. Compared with unamended soils, at the 5% rate of application the adsorption capacity increased by between 9.8% and 40%, 148% and 224%, and by 258% for the OW, COW, and AOW amended soils, respectively. The hysteresis coefficients were significantly lower in the OW-amended soils than in AOW or COW-amended soils, indicating that the adsorbed MCPA could be easily desorbed in OW-amended soils if the amendment is not aged or composted. While the OW addition greatly extended the persistence of MCPA, the application of COW enhanced MCPA degradation in all the soils, as corresponded to the increased soil microbial activity indicated by the higher levels of soil dehydrogenase activity. Fresh OW amendment significantly increased the amount of MCPA leached (from 13.7% in the most alkaline soil to 36.7% in the most acidic, at the 5% rate of application), favored by the higher levels of water soluble organic carbon content. However, leaching losses of the herbicide were reduced by up to 39.9% and 55.3% in the COW- and AOW-amended soils at the 5% loading rate, respectively. The use of OW with a high degree of organic matter maturity may be regarded as a potentially useful management practice to reduce MCPA leaching in soils with low organic matter content. The application of fresh OW, however, could well increase the risk of groundwater contamination by this herbicide, especially in acidic soils.

Thermal Distribution of Size-resolved Carbonaceous Aerosols and Water Soluble Organic Carbon in Emissions from Biomass Burning

The study of carbonaceous aerosols in the atmosphere is critical to understand the role of aerosols in human health and climate. Using standardized thermal optical transmittance methods, organic carbon (OC), elemental carbon (EC), and water soluble organic carbon (WSOC) were determined using a combustion sampling system for four types of agricultural crop residues (rice straw, red pepper stems, soybean stems, and green perilla stems) and eight types of forest trees (pine stems, pine needles, ginkgo stems, ginkgo leaves, maple stems, maple leaves, cherry stems, and cherry leaves). The aerosol particles between 0.056 and 5.6 μm in size were analyzed using a Micro-Orifice Uniform Deposit Impactor (MOUDI). In the current study, the Carbonaceous Thermal Distribution (CTD) by carbon analyzer was discussed in order to understand the carbon fractions from the twelve types of biomass burning. Also, the concentration of OC, EC, WSOC, and water insoluble organic carbon (WIOC) detected in the emissions were described.

Organic and inorganic markers and stable C-, N-isotopic compositions of tropical coastal aerosols from megacity Mumbai: sources of organic aerosols and atmospheric processing

Abstract. To better understand the sources of PM10 samples in Mumbai, India, aerosol chemical composition, i.e., total carbon (TC), organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and inorganic ions were studied together with specific markers such as methanesulfonate (MSA), oxalic acid (C2), azelaic acid (C9), and levoglucosan. The results revealed that biofuel/biomass burning and fossil fuel combustion are the major sources of the Mumbai aerosols. Nitrogen-isotopic (δ15N) composition of aerosol total nitrogen, which ranged from 18.1 to 25.4‰, also suggests that biofuel/biomass burning is a predominate source in both the summer and winter seasons. Aerosol mass concentrations of major species increased 3–4 times in winter compared to summer, indicating enhanced emission from these sources in the winter season. Photochemical production tracers, C2 diacid and nssSO42−, do not show diurnal changes. Concentrations of C2 diacid and WSOC show a strong correlation (r2 = 0.95). In addition, WSOC to OC (or TC) ratios remain almost constant for daytime (0.37 &amp;amp;pm; 0.06 (0.28 &amp;amp;pm; 0.04)) and nighttime (0.38 &amp;amp;pm; 0.07 (0.28 &amp;amp;pm; 0.06)), suggesting that mixing of fresh secondary organic aerosols is not significant and the Mumbai aerosols are photochemically well processed. Concentrations of MSA and C9 diacid present a positive correlation (r2 = 0.75), indicating a marine influence on Mumbai aerosols in addition to local/regional influence. Backward air mass trajectory analyses further suggested that the Mumbai aerosols are largely influenced by long-range continental and regional transport. Stable C-isotopic ratios (δ13C) of TC ranged from −27.0 to −25.4‰, with slightly lower average (−26.5 &amp;amp;pm; 0.3‰) in summer than in winter (−25.9 &amp;amp;pm; 0.3‰). Positive correlation between WSOC/TC ratios and δ13C values suggested that the relative increment in 13C of wintertime TC may be caused by prolonged photochemical processing of organic aerosols in this season. This study suggests that in winter, the tropical aerosols are more aged due to longer residence time in the atmosphere than in summer aerosols. However, these conclusions are based on the analysis of a limited number of samples (n=25) and more information on this topic may be needed from other similar coastal sites in future.

13C‐ and 14C‐based study of sources and atmospheric processing of water‐soluble organic carbon (WSOC) in South Asian aerosols

Water‐soluble organic carbon (WSOC) is typically a large component of carbonaceous aerosols with a high propensity for inducing cloud formation. The sources of WSOC, which may be both of primary and secondary origins, are in general poorly constrained. This study assesses the concentrations and dual‐carbon isotope (14C and 13C) signatures of South Asian WSOC during a 15‐month continuous campaign in 2008–2009. Total suspended particulate matter samples were collected at Sinhagad (SINH) India and at the Maldives Climate Observatory at Hanimaadhoo (MCOH). Monsoon‐driven meteorology yields significant WSOC concentration differences between the dry winter season (0.94 ± 0.43 µg m−3 MCOH and 3.6 ± 2.3 µg m−3 SINH) and the summer monsoon season (0.10 ± 0.04 µg m−3 MCOH and 0.35 ± 0.21 µg m−3 SINH). Radiocarbon‐based source apportionment of WSOC not only shows the dominance of biogenic/biomass combustion sources but also a substantial anthropogenic fossil‐fuel contribution (17 ± 4% MCOH and 23 ± 4% SINH). Aerosols reaching MCOH after long‐range over‐ocean transport were enriched by 3–4‰ in δ13C‐WSOC relative to SINH. This is consistent with particle‐phase aging processes influencing the δ13C‐WSOC signal in the South Asian regional receptor atmosphere.

Characterization of Organic Aerosol Particles Observed during Asian Dust Events in Spring 2010

Between 20 March and 4 April, 2010, 24-hr PM2.5 measurements were carried out at an urban site in Gwangju, Korea, to examine the variations in the composition of its chemical constituents among dust storm (DS) events, haze pollution, and typical sampling (TS) conditions. A very heavy Asian DS (DS1) and a minor DS (DS2) occurred at the site on 20 and 23 March, 2010, respectively. The concentrations of organic matter, NO3–, SO42–, and the predicted crustal material made a contribution to the observed PM2.5 of 12.9, 9.7, 12.9, and 36.9% for DS1, 23.8, 17.1, 9.9, and 29.7% for DS2, and 24.9, 20.2, 10.3, and 17.6% for the haze event, respectively. Over the study period, the water-soluble organic carbon (WSOC)/OC and hydrophilic WSOC (WSOCHPI)/WSOC ratios ranged from 0.35 to 0.54 and from 0.15 to 0.61, respectively, with the highest ratios occurring during DS1. The concentration of WSOCHPI during DS1 was about 2–3 times higher than that during the TS period. The strong correlation between WSOC/OC and WSOCHPI/WSOC (R2 = 0.84) clearly indicates that the increase in the WSOC/OC ratio can be attributed to the increased concentration of WSOCHPI, suggesting that the aerosol sample collected during DS1 was more aged or atmospherically processed than the samples collected during the TS. In addition to the association between the WSOC/OC and WSOCHPI/WSOC ratios, strong correlations between the oxalate and SO42– concentrations (R2 = 0.74), and between the WSOCHPI and SO42– concentrations (R2 = 0.69), suggest that the WSOCHPI observed at the site was produced by atmospheric transformation processes similar to those seen with SO42– and oxalate. In contrast, the hydrophobic WSOC (WSOCHPO) concentration dominated in the other sampling periods, except for DS1, and accounted for 71.1–84.7% of WSOC. Based on the results of previous studies, the higher WSOCHPO/WSOC ratio during the TS indicates that the primary combustion emissions were important sources of the WSOCHPO fraction at this site.

Evidence of formation of submicrometer water‐soluble organic aerosols at a deciduous forest site in northern Japan in summer

Semicontinuous measurements of submicrometer water‐soluble organic aerosols and particle size distributions were conducted at a deciduous forest site in northern Japan in August 2010. Increases in particle number concentration were frequently observed in daytime, accompanied by an increase in the concentrations of water‐soluble organic carbon (WSOC). We found that daily averaged WSOC concentrations positively correlated with gross primary production of CO2 by the forest ecosystem (r2 = 0.63) and ambient temperature during daytime. These relations suggest that the formation of WSOC is closely linked to photosynthetic activity by the forest ecosystem, which depends on both temperature and solar radiation. Off‐line chemical analysis of samples of particles with aerodynamic diameter smaller than 1 μm collected during a 2 day event of elevated WSOC levels suggests that photochemical aging of both α‐ andβ‐pinene and isoprene oxidation products contributes to the particle growth and the WSOC mass. Organic tracers of primary biological aerosol particles (PBAPs) showed distinct diurnal variations with a maximum around noontime, also indicating that higher temperature and light intensity induce emissions of PBAPs. However, their contribution to the submicrometer WSOC mass was likely insignificant. During the day, the concentrations of 3‐methyl‐1,2,3‐butanetricarboxylic acid (3‐MBTCA) showed a strong dependence on temperature, and the ratios of WSOC to particle volume concentration increased with an increase in the concentration ratios of 3‐MBTCA to pinonic acid (PA). This result supports a previous proposal that the 3‐MBTCA/PA ratios in submicrometer particles can be a useful tracer for chemical aging of biogenic secondary organic aerosol from forest vegetation.