Aerosol Water-soluble Organic Carbon Research Articles

Elevated particulate methanesulfonate, oxalate and iron over Sydney Harbour in the austral summer of 2019-20 during unprecedented bushfire activity

In the austral summer period, Dec 7, 2019 to Mar 1, 2020, which included unprecedented bushfire activity, total suspended particulate concentrations of methanesulfonate (MSA), oxalate, labile iron, SO42−, Cl−, Na+, K+, NH4+, water soluble solids (WSS) and water soluble organic carbon (WSOC) were measured from weekly filter samples at Seaforth on the northern edge of Sydney Harbour. Particle number concentrations (PNC) and meteorological conditions were also measured at hourly intervals. These entities were previously measured in the spring-summer period, Sep 30, 2018 to Feb 24, 2019. Data analysis is focussed on inter-comparison between the summer of 2018–19 (S1) and 2019–20 (S2) spanning the period 7 Dec to 24 Feb. During S2 seasonally averaged MSA, oxalate, labile iron, K+, PNC (0.5–2.5 μm), and WSOC were elevated by 102%, 57%, 64%, 72%, 108%, and 1907%, respectively, by comparison to S1. Aqueous phase secondary formation of oxalate and a marine source of MSA were evident during S1; however, during S2 it was indicated that the bushfires created conditions where oxalate formation was shifted away from aqueous phase processing and MSA became associated with bushfire generated WSOC aerosol. Correlation changes at the a = 0.05 significance level between S1 and S2 for MSA, and for oxalate, are examined and discussed in relation to effects apparently caused by the bushfires. It is indicated that the biogeochemical cycling of sulfur and carbon, and particulate deposition of iron micronutrient to the South Pacific Ocean, may be altered by bushfires in Australia.

Size distribution and formation processes of aerosol water-soluble organic carbon during winter and summer in urban Beijing

Size-resolved aerosol organic carbon (OC) and water-soluble OC (WSOC) was determined weekly in urban Beijing between 2013 and 2018. The results showed that in winter, the concentrations of WSOC and OC in fine (<2.1 μm) and coarse (>2.1 μm) mode were highest in 2013. During the following years, the concentrations of WSOC and OC were lower but an increasing trend was found from 2014 to 2016, which might be due to the increasing precursor concentrations. From summer 2013 to 2018, the concentrations of OC and WSOC in both fine and coarse mode decreased, which might be affected by decreasing emission intensity and photochemical oxidation. To characterize the seasonality of WSOC, two intensive field observations were further performed in winter 2013 and summer 2018. In winter of 2013, WSOC was mainly enriched in PM1 (<1 μm) on clean days and lightly polluted days. In addition, the fine mode maximum shifted from 0.43-0.65 μm to 1.1–2.1 μm with the haze development due to the hygroscopic growth of particles. In summer of 2018, the WSOC was mainly concentrated in PM1, but in a few samples, the maximum size appeared in coarse mode. This difference might due to the different relative humidity and air mass sources. While the formation process of WSOC in winter was affected by photochemical oxidation below 2.1 μm, in 1.1–2.1 μm, it tended to change from photochemical oxidation to aqueous-phase oxidation. For the coarse mode WSOC formation in winter, however, it was mainly affected by heterogeneous processes. The findings advanced our understanding of the annual trends, size distribution and formation processes of WSOC, with significant implications for air pollution control in Beijing and surrounding regions.

Investigation of the spatio-temporal heterogeneity and optical property of water-soluble organic carbon in atmospheric aerosol and snow over the Yulong Snow Mountain, southeastern Tibetan Plateau

Atmospheric aerosols are a branch of active research in recent decades. The deposition of light-absorbing substances on high-altitude glaciers causes substantial adverse impacts on the cryospheric environment, cryosphere-hydrology, and climate system. Although, the concentrations of water-soluble organic carbon (WSOC) in snow/ice on glaciers of Tibetan Plateau (TP) have been reported, their transfer processes and optical properties in the context of summer precipitation-atmosphere-snow-river water continuum are seldom studied. In this study, we have systematically examined some scientific issues associated with WSOC concentrations and light absorption properties of WSOC in various forms of samples from the Mt. Yulong region. Statistical results demonstrate that the spatial distribution of WSOC in the snow of Baishui glacier was heterogeneous. The average WSOC concentrations of each snowpit were significantly decreased, and its light-absorbing properties were significantly elevated with the time extension. Aerosol WSOC concentrations and light absorption have distinct spatial disparity and seasonal variation. Pre-monsoon and monsoon have the highest and lowest WSOC content, respectively. Whereas the light-absorbing properties present contrasting seasonal trends. Rivers of which runoff was supplied by glacier meltwater have significantly lower WSOC concentrations (e.g., 0.42 ± 0.03 mg L−1) compared with other forms of water bodies. Mass absorption cross-section of WSOC (MAC-WSOC) in multiple snow and meltwater samples was significantly different and type-dependent. Atmospheric aerosol has the lowest MAC-WSOC value among the four types of samples, which was likely associated with exhaust emissions from private vehicles and tour buses. Statistical results indicated that the average AAE330-400 values of various snow/ice samples are subequal. Snow of glaciers supplies a desirable platform for the deposition of gaseous materials which experienced long-range transport in high altitude zones. Biomass-burning emissions made an immense contribution to the WSOC deposition over the study area, as demonstrated by the distribution of active fire points. However, this preliminary study represents the first systematic investigation of WSOC deposition in southeastern TP. Further robust in-situ field investigations and laboratory measurements are urgently necessary to improve our understanding of the transfer process and optical property of WSOC.

High time-resolved measurement of stable carbon isotope composition in water-soluble organic aerosols: method optimization and a case study during winter haze in eastern China

Abstract. Water-soluble organic carbon (WSOC) is a significant fraction of organic carbon (OC) in atmospheric aerosols. WSOC is of great interest due to its significant effects on atmospheric chemistry, the Earth's climate and human health. The stable carbon isotope (δ13C) can be used to track the potential sources and investigate atmospheric processes of organic aerosols. However, the previous methods measuring the δ13C values of WSOC in ambient aerosols require a large amount of carbon content, are time-consuming and require labor-intensive preprocessing. In this study, a method of simultaneously measuring the mass concentration and the δ13C values of WSOC from aerosol samples is established by coupling the GasBench II preparation device with isotopic ratio mass spectrometry. The precision and accuracy of isotope determination is better than 0.17 ‰ and 0.5 ‰, respectively, for samples containing WSOC amounts larger than 5 µg. This method is then applied for the aerosol samples collected every 3 h during a severe wintertime haze period in Nanjing, eastern China. The WSOC values vary between 3 and 32 µg m−3, whereas δ13C−WSOC ranges from −26.24 ‰ to −23.35 ‰. Three different episodes (Episode 1, Episode 2 and Episode 3) are identified in the sampling period, showing a different tendency of δ13C−WSOC with the accumulation process of WSOC aerosols. The increases in both the WSOC mass concentrations and the δ13C−WSOC values in Episode 1 indicate that WSOC is subject to a substantial photochemical aging during the air mass transport. In Episode 2, the decline of the δ13C−WSOC is accompanied by the increase in the WSOC mass concentrations, which is associated with regional-transported biomass burning emissions. In Episode 3, heavier isotope (13C) is exclusively enriched in total carbon (TC) in comparison to WSOC aerosols. This suggests that the non-WSOC fraction in total carbon may contain 13C-enriched components such as dust carbonate, which is supported by the enhanced Ca2+ concentrations and air mass trajectory analysis. The present study provides a novel method to determine the stable carbon isotope composition of WSOC, and it offers a great potential to better understand the source emission, the atmospheric aging and the secondary production of water-soluble organic aerosols.

2018년 11월 광주 지역에서 발생한 미세먼지 고농도 사례 시 수용성 성분의 크기 분포 조사

In this study, mass size distributions of ambient aerosol particles and their water-soluble organic and inorganic species were investigated under high pollution episode. To achieve the aim of this study, 24-hr integrated size-segregated aerosol samples were collected at an ubran site of Gwangju between November 02 and 16, 2018, and analyzed for mass, water-soluble organic carbon (WSOC), and ionic species. During study period, a high pollution episode of fine particulate matter (PM) occurred between November 02 and 07, possibly due to high pressure developed around Korean peninsula, extremely stable air conditions, and long-range transportation of aerosol particles from North Korea and northeastern China region. On November 02~03 when influence of local pollution dominated, ambient aerosol particles, WSOC, NO3-, SO₄2-, and NH4+ exhibited bi-modal size distributions with a condensation mode at a particle size of 0.32 μm and a droplet mode at a particle size of 1.0 μm in PM1.8. While, between November 05 and 07 when long-range transportation of PM was mixed with locally-produced pollution, they showed very pronounced droplet mode size distributions at 1.0 μm, without a condensation mode. NO3- concentration in PM1.8 during pollution episode increased significantly from 5.9 μg/m³ on November 02 to 21.5μg/m³ on November 06, while SO₄2- in PM1.8 increased from 1.6 to 5.8 μg/m³, indicating the dominance of local pollution during pollution episode. Furthermore, for WSOC, NO3-, SO₄2-, and NH4+, fraction of droplet mode size (PM0.55-1.8) to PM1.8 increased gradually as PM pollution got increased, while the condensation mode (PM0.17-0.32) contribution decreased. In addition, it was demonstrated that relative humidity could be an important factor promoting formation of droplet mode WSOC, NO3-, and SO₄2-.

Large contribution of fossil fuel derived secondary organic carbon to water soluble organic aerosols in winter haze in China

Abstract. Water-soluble organic carbon (WSOC) is a large fraction of organic aerosols (OA) globally and has significant impacts on climate and human health. The sources of WSOC remain very uncertain in polluted regions. Here we present a quantitative source apportionment of WSOC, isolated from aerosols in China using radiocarbon (14C) and offline high-resolution time-of-flight aerosol mass spectrometer measurements. Fossil emissions on average accounted for 32–47 % of WSOC. Secondary organic carbon (SOC) dominated both the non-fossil and fossil derived WSOC, highlighting the importance of secondary formation to WSOC in severe winter haze episodes. Contributions from fossil emissions to SOC were 61 ± 4 and 50 ± 9 % in Shanghai and Beijing, respectively, significantly larger than those in Guangzhou (36 ± 9 %) and Xi'an (26 ± 9 %). The most important primary sources were biomass burning emissions, contributing 17–26 % of WSOC. The remaining primary sources such as coal combustion, cooking and traffic were generally very small but not negligible contributors, as coal combustion contribution could exceed 10 %. Taken together with earlier 14C source apportionment studies in urban, rural, semi-urban and background regions in Asia, Europe and the USA, we demonstrated a dominant contribution of non-fossil emissions (i.e., 75 ± 11 %) to WSOC aerosols in the Northern Hemisphere; however, the fossil fraction is substantially larger in aerosols from East Asia and the eastern Asian pollution outflow, especially during winter, due to increasing coal combustion. Inclusion of our findings can improve a modelling of effects of WSOC aerosols on climate, atmospheric chemistry and public health.

Structural signatures of water-soluble organic aerosols in contrasting environments in South America and Western Europe

This study describes and compares the key structural units present in water-soluble organic carbon (WSOC) fraction of atmospheric aerosols collected in different South American (Colombia – Medellín and Bogotá, Peru – Lima, Argentina – Buenos Aires, and Brazil – Rio de Janeiro, São Paulo, and Porto Velho, during moderate (MBB) and intense (IBB) biomass burning) and Western European (Portugal – Aveiro and Lisbon) locations. Proton nuclear magnetic resonance (1H NMR) spectroscopy was employed to assess the relative distribution of non-exchangeable proton functional groups in aerosol WSOC of diverse origin, for the first time to the authors’ knowledge in South America. The relative contribution of the proton functional groups was in the order H-C > H–C–C= > H-C-O > Ar-H, except in Porto Velho during MBB, Medellín, Bogotá, and Buenos Aires, for which the relative contribution of H-C-O was higher than that of H-C-C=. The 1H NMR source attribution confirmed differences in aging processes or regional sources between the two geographic regions, allowing the differentiation between urban combustion-related aerosol and biological particles. The aerosol WSOC in Aveiro, Lisbon, and Rio de Janeiro during summer are more oxidized than those from the remaining locations, indicating the predominance of secondary organic aerosols. Fresh emissions, namely of smoke particles, becomes important during winter in Aveiro and São Paulo, and in Porto Velho during IBB. The biosphere is an important source altering the chemical composition of aerosol WSOC in South America locations. The source attribution in Medellín, Bogotá, Buenos Aires, and Lima confirmed the mixed contributions of biological material, secondary formation, as well as urban and biomass burning emissions. Overall, the information and knowledge acquired in this study provide important diagnostic tools for future studies aiming at understanding the water-soluble organic aerosol problem, their sources and impact at a wider geographic scale.

Contribution of dissolved organic matter to submicron water-soluble organic aerosols in the marine boundary layer over the eastern equatorial Pacific

Abstract. Stable carbon isotopic compositions of water-soluble organic carbon (WSOC) and organic molecular markers were measured to investigate the relative contributions of the sea surface sources to the water-soluble fraction of submicron organic aerosols collected over the eastern equatorial Pacific during the Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOCs (TORERO)/KA-12-01 cruise. On average, the water-soluble organic fraction of the total carbon (TC) mass in submicron aerosols was ∼ 30–35 % in the oceans with the low chlorophyll a (Chl a) concentrations, whereas it was ∼ 60 % in the high-Chl a regions. The average stable carbon isotope ratio of WSOC (δ13CWSOC) was −19.8 ± 2.0 ‰, which was systematically higher than that of TC (δ13CTC) (−21.8 ± 1.4 ‰). We found that in the oceans with both high and low Chl a concentrations the δ13CWSOC was close to the typical values of δ13C for dissolved organic carbon (DOC), ranging from −22 to −20 ‰ in surface seawater of the tropical Pacific Ocean. This suggests an enrichment of marine biological products in WSOC aerosols in the study region regardless of the oceanic area. In particular, enhanced levels of WSOC and biogenic organic marker compounds together with high values of WSOC / TC ( ∼ 60 %) and δ13CWSOC were observed over upwelling areas and phytoplankton blooms, which was attributed to planktonic tissues being more enriched in δ13C. The δ13C analysis estimated that, on average, marine sources contribute ∼ 90 ± 25 % of the aerosol carbon, indicating the predominance of marine-derived carbon in the submicron WSOC. This conclusion is supported by Lagrangian trajectory analysis, which suggests that the majority of the sampling points on the ship had been exposed to marine boundary layer (MBL) air for more than 80 % of the time during the previous 7 days. The combined analysis of the δ13C and monosaccharides, such as glucose and fructose, demonstrated that DOC concentration was closely correlated with the concentration levels of submicron WSOC across the study region regardless of the oceanic area. The result implies that DOC may characterize background organic aerosols in the MBL over the study region.

Estimation of aerosol optical properties considering hygroscopicity and light absorption

In this study, the influences of water solubility and light absorption on the optical properties of organic aerosols were investigated. A size-resolved model for calculating optical properties was developed by combining thermodynamic hygroscopic growth and aerosol dynamics models. The internal mixtures based on the homogeneous and core–shell mixing were compared. The results showed that the radiative forcing (RF) of Water Soluble Organic Carbon (WSOC) aerosol can be estimated to range from −0.07 to −0.49 W/m2 for core–shell mixing and from −0.09 to −0.47 W/m2 for homogeneous mixing under the simulation conditions (RH = 60%). The light absorption properties of WSOC showed the mass absorption efficiency (MAE) of WSOC can be estimated 0.43–0.5 m2/g, which accounts for 5–10% of the MAE of elemental carbon (EC). The effect on MAE of increasing the imaginary refractive index of WSOC was also calculated, and it was found that increasing the imaginary refractive index by 0.001i enhanced WSOC aerosol absorption by approximately 0.02 m2/g. Finally, the sensitivity test results revealed that changes in the fine mode fraction (FMF) and in the geometric mean diameter of the accumulation mode play important roles in estimating RF during hygroscopic growth.

Aerosol water soluble organic matter characteristics over the North Atlantic Ocean: Implications for iron-binding ligands and iron solubility

Aerosol water soluble organic carbon (WSOC) and iron (Fe) loadings were examined in aerosols collected during the 2011 US GEOTRACES cruise in the North Atlantic Ocean to explore the feasibility of a role for water soluble organic matter (WSOM) organic complexation in determining the higher fractional solubility of Fe (%FeS) observed in North American-influenced relative to North African-influenced aerosols. Proton nuclear magnetic resonance spectroscopy (1H NMR) was employed to characterize the WSOM, and principal component analysis was then applied to differentiate North American-influenced from North African-influenced aerosol WSOM and provide clues to the molecular identities of organic ligands. As has been found in previous studies, North African-influenced samples had orders of magnitude higher total Fe (FeT) loadings (8.9–101nmol Fe m−3 air) and orders of magnitude lower %FeS (0.12–0.29%) than those found in North American-influenced (FeT: 0.03–1.4nmol Fe m−3 air; %FeS: 0.67–3.62%) and Marine (minimal recent continental influence; FeT: 0.02–0.25nmol Fe m−3 air; %FeS: 1.1–10.7%) samples. Aerosol %FeS values were positively correlated with WSOC/FeT ratios with North American combustion-influenced (39–540) and Marine (30–850) aerosol samples having orders of magnitude more moles of WSOC per mole of FeT than North African (0.42–3.8) aerosol samples. The high WSOC/FeT ratios in the North American combustion-influenced samples suggest a realistic role for organic ligands binding with Fe and accounting for some portion of the higher aerosol %FeS also observed for these samples. Principal component analyses of 1H NMR spectra show North American-influenced aerosol WSOM to have higher contributions from hydrogens in aliphatic carbon chains attached to heteroatomic functional groups such as those in nitrate, amine, ether, ester, and carboxylate compounds compared to North African mineral dust-influenced aerosol WSOM. These multifunctional aliphatic WSOM compounds are suggested as candidate Fe binding ligands to be explored with future work.

Micro-scale (μg) radiocarbon analysis of water-soluble organic carbon in aerosol samples

Radiocarbon (14C) measurement of water-soluble organic carbon (WSOC) in ambient aerosols is a quantitative tool for unambiguously distinguishing fossil and non-fossil sources. In this study, a fast and reliable method for measuring 14C in micro-scale (μg) WSOC aerosol samples is successfully developed, which includes three steps: (1) extraction (2) freeze drying, and (3) online 14C analysis of CO2 from WSOC combustion. Procedure blanks are carefully assessed by measuring high-purity water and reference materials. Accurate 14C results could be obtained for WSOC with only 10 μg C, and thus the potential applications are substantially broadened because much less filter material is needed compared to previous reported methods. This method is applied to aerosols samples collected during winter from Switzerland and China. The results demonstrate that non-fossil sources are important if not dominant contributors of WSOC. These non-fossil components are consistently enriched in WSOC compared to bulk OC and water-insoluble OC for all samples, due to high water solubility of primary and secondary biomass burning aerosols. However, the presence of fossil WSOC is still considerable indicating a substantial contribution of secondary OC (SOC) formed from precursors emitted by fossil emissions. Larger fossil contributions to WSOC is found in China than in Switzerland and previously reported values in Europe, USA and South Asia, which may be attributed to higher fossil-derived SOC formation in China.

Water-soluble organic carbon aerosols during a full New Delhi winter: Isotope-based source apportionment and optical properties

Water-soluble organic carbon (WSOC) is a major constituent (~ 20–80%) of the total organic carbon aerosol over the Indian subcontinent during the dry winter season. Due to its multiple primary and secondary formation pathways, the sources of WSOC are poorly characterized. In this study, we present radiocarbon constraints on the biomass versus fossil sources of WSOC in PM2.5 for the 2010/2011 winter period for the megacity Delhi, situated in the northern part of the heavily polluted Indo-Gangetic Plain. The fossil fuel contribution to Delhi WSOC (21 ± 4%) is similar to that recently found at two South Asian background sites. In contrast, the stable carbon isotopic composition of Delhi WSOC is less enriched in 13C relative to that at the two receptor sites. Although potentially influenced also by source variability, this indicates that near-source WSOC is less affected by atmospheric aging. In addition, the light absorptive properties of Delhi WSOC were studied. The mass absorption cross section at 365 nm (MAC365) was 1.1–2.7 m2/g with an Absorption Angstrom Exponent ranging between 3.1 and 9.3. Using a simplistic model the relative absorptive forcing of the WSOC compared to elemental carbon in 2010/2011 wintertime Delhi was estimated to range between 3 and 11%. Taken together, this near-source study shows that WSOC in urban Delhi comes mainly (79%) from biomass burning/biogenic sources. Furthermore, it is less influenced by photochemical aging compared to WSOC at South Asian regional receptor sites and contributes with a relatively small direct absorptive forcing effect.

Major 20th century changes of the content and chemical speciation of organic carbon archived in Alpine ice cores: Implications for the long‐term change of organic aerosol over Europe

Dissolved organic carbon (DOC) and an extended array of organic compounds were investigated in an Alpine ice core covering the 1920–1988 time period. Based on this, a reconstruction was made of the long‐term trends of water‐soluble organic carbon (WSOC) aerosol in the European atmosphere. It is shown that light mono‐ and dicarboxylates, humic‐like substances, and formaldehyde account together for more than half of the DOC content of ice. This extended chemical speciation of DOC is used to estimate the DOC fraction present in ice that is related to WSOC aerosol and its change over the past. It is suggested that after World War II, the WSOC levels have been enhanced by a factor of 2 and 3 in winter and summer, respectively. In summer, the fossil fuel contribution to the enhancement is estimated to be rather small, suggesting that it arises mainly from an increase in biogenic sources of WSOC.

Isotopic characterization of aerosol organic carbon components over the eastern United States

Carbon isotopic signatures (δ13C, Δ14C) of aerosol particulate matter total organic carbon (TOC) and operationally defined organic carbon (OC) components were measured in samples from two background sites in the eastern U.S. TOC and water‐soluble OC (WSOC)δ13C values (−27 to −24‰) indicated predominantly terrestrial C3 plant and fossil derived sources. Total solvent extracts (TSE) and their aliphatic, aromatic, and polar OC components were depleted in δ13C (−30 to −26‰) relative to TOC and WSOC. Δ14C signatures of aerosol TOC and TSE (−476 to +25‰) suggest variable fossil contributions (∼5–50%) to these components. Aliphatic OC while comprising a small portion of the TOC (&lt;1%), was dominated by fossil‐derived carbon (86 ± 3%), indicating its potential utility as a tracer for fossil aerosol OC inputs. In contrast, aromatic OC contributions (&lt;1.5%) contained approximately equal portions contemporary (52 ± 8%) and fossil (48 ± 8%) OC. The quantitatively significant polar OC fraction (6–25% of TOC) had fossil contributions (30 ± 12%) similar to TOC (26 ± 7%) and TSE (28 ± 9%). Thus, much of both of the fossil and contemporary OC is deduced to be oxidized, polar material. Aerosol WSOC consistently showed low fossil content (&lt;8%) relative to the TOC (5–50%) indicating that the majority of fossil OC in aerosol particulates is insoluble. Therefore, on the basis of solubility and polarity, aerosols are predicted to partition differently once deposited to watersheds, and these chemically distinct components are predicted to contribute in quantitatively and qualitatively different ways to watershed carbon biogeochemistry and cycling.

Seasonal variations of stable carbon isotopic composition and biogenic tracer compounds of water-soluble organic aerosols in a deciduous forest

Abstract. To investigate the seasonal changes in biogenic water-soluble organic carbon (WSOC) aerosols in a boreal forest, aerosol samples were collected continuously in the canopy of a deciduous forest in northern Japan during 2009–2010. Stable carbon isotopic composition of WSOC (δ13CWSOC) in total suspended particulate matter (TSP) exhibited a distinct seasonal cycle, with lower values from June through September (−25.5±0.5 ‰). This cycle follows the net CO2 exchange between the forest ecosystem and the atmosphere, indicating that δ13CWSOC likely reflects the biological activity at the forest site. WSOC concentrations showed the highest values in early summer and autumn. Positive matrix factorization (PMF) analysis indicated that the factor in which biogenic secondary organic aerosols (BSOAs) dominated accounted for ~40 % of the highest concentrations of WSOC, where BSOAs mostly consisted of α-/β-pinene SOA. In addition, primary biological aerosol particles (PBAPs) made similar contributions (~57 %) to the WSOC near the forest floor in early summer. This finding indicates that the production of both primary and secondary WSOC aerosols is important during the growing season in a deciduous forest. The methanesulfonic acid (MSA) maximum was also found in early summer and had a distinct vertical gradient with larger concentrations near the forest floor. Together with the similar vertical gradients found for WSOC and δ13CWSOC as well as the α-/β-pinene SOA tracers, our results indicate that the forest floor, including ground vegetation and soil, acts as a significant source of WSOC in TSP within a forest canopy at the study site.

Identification of water-soluble organic carbon in non-urban aerosols using ultrahigh-resolution FT-ICR mass spectrometry: organic anions

Environmental contextAerosol water-soluble organic carbon is a complex mixture of thousands of organic compounds which may have a significant influence on the climate-relevant properties of atmospheric aerosols. Using ultrahigh resolution mass spectrometry, more than 4000 individual molecular formulas were identified in non-urban aerosol water-soluble organic carbon. A significant fraction of the assigned molecular formulas were matched to assigned molecular formulas of laboratory generated secondary organic aerosols. AbstractWater-soluble organic carbon (WSOC) is a complex mixture of thousands of organic compounds which may have significant influence on the climate-relevant properties of atmospheric aerosols. An improved understanding of the molecular composition of WSOC is needed to evaluate the effect of aerosol composition upon aerosol physical properties. In this work, ultrahigh-resolution Fourier transform–ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to characterise aerosol WSOC collected during the summer of 2010 at the Storm Peak Laboratory (3210 m ASL) near Steamboat Springs, CO. Approximately 4000 molecular formulas were assigned in the mass range of 100–800 Da after negative-ion electrospray ionisation and more than 50 % of them contained nitrogen or sulfur. The double bond equivalents (DBEs) of the molecular formulas were inversely proportional to the O : C ratio, despite a relatively constant H : C ratio of ~1.5. Despite the range of DBE values, the elemental ratios and the high number of oxygen atoms per formula indicate that a majority of the compounds are aliphatic to olefinic in nature. These trends indicate significant non-oxidative accretion reaction pathways for the formation of high molecular weight WSOC components. In addition, a significant number of molecular formulas assigned in this work matched those previously identified as secondary organic aerosol components of monoterpene and sesquiterpene ozonolysis.

Anthropogenic aerosols observed in Asian continental outflow at Jeju Island, Korea, in spring 2005

Anthropogenic aerosols were measured together with CO at Gosan (33°17′N, 126°10′E) on Jeju Island, South Korea, between 17 March and 5 April 2005. Outflow of these aerosols from the Asian continent was associated with a high‐pressure system centered over the northern region of China and Mongolia. Air masses are classified into five distinct categories on the basis of origin: marine, free troposphere, Yellow Sea, Korea, and China. The concentrations of aerosols and CO show large variations because of the alternation of air masses, while wet scavenging of aerosols was another important factor during precipitation events at Gosan. The average mass concentrations of black carbon (BC), organic carbon (OC), water‐soluble organic carbon (WSOC), and sulfate (SO42−) aerosols were 1.2 ± 0.8 μgC m−3, 4.2 ± 1.6 μgC m−3, 1.3 ± 1.0 μgC m−3, and 4.0 ± 3.4 μg m−3, respectively. Almost all species concentrations were highest in Chinese air masses, while they were lowest in marine air masses. The observed ΔBC/ΔCO slope of 9.7 ng m−3 ppbv−1 in Chinese outflow agrees reasonably with the estimates of the BC/CO emission ratios over northeastern China. The transport efficiencies of SOx (SO2 + SO42−) are calculated to be 40–45% from the observed SOx‐CO correlation. The relationships of the SO42−/BC and WSOC/BC ratios with transport time from the continent suggest that a majority of SO42− and WSOC aerosols were formed by about 1.5 days after the air masses left the East Asian continent.

Aqueous-phase reactive uptake of dicarbonyls as a source of organic aerosol over eastern North America

We use a global 3-D atmospheric chemistry model (GEOS-Chem) to simulate surface and aircraft measurements of organic carbon (OC) aerosol over eastern North America during summer 2004 (ICARTT aircraft campaign), with the goal of evaluating the potential importance of a new secondary organic aerosol (SOA) formation pathway via irreversible uptake of dicarbonyl gases (glyoxal and methylglyoxal) by aqueous particles. Both dicarbonyls are predominantly produced in the atmosphere by isoprene, with minor contributions from other biogenic and anthropogenic precursors. Dicarbonyl SOA formation is represented by a reactive uptake coefficient γ = 2.9 × 10 −3 and takes place mainly in clouds. Surface measurements of OC aerosol at the IMPROVE network in the eastern U.S. average 2.2 ± 0.7 μg C m −3 for July–August 2004 with little regional structure. The corresponding model concentration is 2.8 ± 0.8 μg C m −3, also with little regional structure due to compensating spatial patterns of biogenic, anthropogenic, and fire contributions. Aircraft measurements of water-soluble organic carbon (WSOC) aerosol average 2.2 ± 1.2 μg C m −3 in the boundary layer (<2 km) and 0.9 ± 0.8 μg C m −3 in the free troposphere (2–6 km), consistent with the model (2.0 ± 1.2 μg C m −3 in the boundary layer and 1.1 ± 1.0 μg C m −3 in the free troposphere). Source attribution for the WSOC aerosol in the model boundary layer is 27% anthropogenic, 18% fire, 28% semi-volatile SOA, and 27% dicarbonyl SOA. In the free troposphere it is 13% anthropogenic, 37% fire, 23% semi-volatile SOA, and 27% dicarbonyl SOA. Inclusion of dicarbonyl SOA doubles the SOA contribution to WSOC aerosol at all altitudes. Observed and simulated correlations of WSOC aerosol with other chemical variables measured aboard the aircraft suggest a major SOA source in the free troposphere compatible with the dicarbonyl mechanism.

Technical Note: Molecular characterization of aerosol-derived water soluble organic carbon using ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Abstract. Despite the acknowledged relevance of aerosol-derived water-soluble organic carbon (WSOC) to climate and biogeochemical cycling, characterization of aerosol WSOC has been limited. Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) was utilized in this study to provide detailed molecular level characterization of the high molecular weight (HMW; m/z&gt;223) component of aerosol-derived WSOC collected from rural sites in Virginia and New York, USA. More than 3000 peaks were detected by ESI FT-ICR MS within a m/z range of 223–600 for each sample. Approximately 86% (Virginia) and 78% (New York) of these peaks were assigned molecular formulas using only carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S) as elemental constituents. H/C and O/C molar ratios were plotted on van Krevelen diagrams and indicated a strong contribution of lignin-like and lipid-like compounds to the aerosol-derived WSOC samples. Approximately 1–4% of the peaks in the aerosol-derived WSOC mass spectra were classified as black carbon (BC) on the basis of double bond equivalents calculated from the assigned molecular formulas. In addition, several high-magnitude peaks in the mass spectra of samples from both sites corresponded to molecular formulas proposed in previous secondary organic aerosol (SOA) laboratory investigations indicating that SOAs are important constituents of the WSOC. Overall, ESI FT-ICR MS provides a level of resolution adequate for detailed compositional and source information of the HMW constituents of aerosol-derived WSOC.

Ambient aerosol concentrations of sugars and sugar-alcohols at four different sites in Norway

Abstract. Sugars and sugar-alcohols are demonstrated to be important constituents of the ambient aerosol water-soluble organic carbon fraction, and to be tracers for primary biological aerosol particles (PBAP). In the present study, levels of four sugars (fructose, glucose, sucrose, trehalose) and three sugar-alcohols (arabitol, inositol, mannitol) in ambient aerosols have been quantified using a novel HPLC/HRMS-TOF (High Performance Liquid Chromatography in combination with High Resolution Mass Spectrometry – Time of Flight) method to assess the contribution of PBAP to PM&gt;sub&gt;10 and PM2.5. Samples were collected at four sites in Norway at different times of the year in order to reflect the various contributing sources and the spatial and seasonal variation of the selected compounds. Sugars and sugar-alcohols were present at all sites investigated, underlining the ubiquity of these highly polar organic compounds. The highest concentrations were reported for sucrose, reaching a maximum concentration of 320 ng m−3 in PM10 and 55 ng m−3 in PM2.5. The mean concentration of sucrose was up to 10 times higher than fructose, glucose and the dimeric sugar trehalose. The mean concentrations of the sugar-alcohols were typically lower, or equal, to that of the monomeric sugars and trehalose. Peak concentrations of arabitol and mannitol did not exceed 30 ng m−3 in PM10, and for PM2.5 all concentrations were below 6 ng m−3. Sugars and sugar-alcohols were associated primarily with coarse aerosols except during wintertime at the suburban site in Elverum, where a shift towards sub micron aerosols was observed. It is proposed that this shift was due to the intensive use of wood burning for residential heating at this site during winter, confirmed by high concurrent concentrations of levoglucosan. Elevated concentrations of sugars in PM2.5 were observed during spring and early summer at the rural background site Birkenes. It is hypothesized that this was due to ruptured pollen.