Water-soluble Dicarboxylic Acids Research Articles

Characterization, sources, and formation processes of dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls in PM2.5 aerosols in New Delhi

Daytime and nighttime fine aerosol (PM2.5) samples were collected during a heavy pollution episode in November 2020, January 2021, and also during clean event (August 2020) in New Delhi. These samples (n = 20) were analyzed for water-soluble dicarboxylic acids (diacids) and related compounds, carbonaceous components, and inorganic ions to identify their sources and atmospheric processing in different episodes/seasons. Among the measured organics, oxalic acid (C2) was found to be the most abundant species followed by terephthalic (tPh), succinic (C4), phthalic (Ph), and azelaic (C9) acids. Such high abundance of tPh were different from those in other Asian cities where C3 is generally the second or third dominant species. tPh very well correlated with OC, Cl− and K+, indicating combustion of biomass and plastic-containing waste may be the possible sources. Significant high contents of diacids, oxoacids, and dicarbonyls were observed during heavy pollution episode, implying an enhanced emission and/or atmospheric processing of these species. Additionally, two important secondary formation pathways for C2 diacid were discussed in New Delhi, i.e. (i) biomass burning derived (biogenic) volatile organic precursors lead to formation of C2 diacid through transformation of oxoacids and dicarbonyls by oxidation, and (ii) oxidative degradation of the unsaturated fatty acids results in formation of C5 and C4 which subsequently decompose to C2 diacid. This study demonstrated that both primary emissions in clean event and secondary production during polluted event are important sources of aerosols in New Delhi.

Exploring the hygroscopicity and chemical composition evolution in organic-inorganic aerosols: A study on internally mixed malonic acid-metal (Na+, Ca2+, Mg2+) nitrates

Chemical transformations in mixed aerosols alter the particulate physical properties. Nitrates and water soluble dicarboxylic acids, such as malonic acid (MA), are major components of ambient aerosol particles. Various metal ions such as, Na+, Ca2+, Mg2+ also become part of these complex aerosol systems during their atmospheric lifetime. Interactions among the co-existing ionic and molecular species govern the chemical changes in the aerosol particles. In this work, we provide a comparative account of the effect of metal ion identity (Na+, Ca2+, Mg2+) on such chemical changes arising from ion-molecular interactions in NaNO3-MA, Ca(NO3)2-MA and Mg(NO3)2-MA mixed inorganic-organic aerosols. In-situ micro-Raman spectroscopy has enabled us to gain molecular level insight on formation of organic salt and simultaneously estimate nitrate depletion in these mixed aerosols during different stages of their hygroscopic cycle. In addition to the nitrate depletion often reported during the drying phase, this study has brought to light an intriguing observation: depletion of nitrate in the humidification phase as well, a phenomenon that has hitherto remained undocumented. For the mixed systems studied here, the extent of nitrate depletion follows the order Mg-MA (58%) > Ca-MA (43%) > Na-MA (15%). The comparatively huge forward shift in the acid displacement reaction equilibrium for the systems, Ca-MA and Mg-MA is driven by complexation. Our results highlight the profound effect of ion-molecular interactions on the acid displacement reaction equilibria in aerosols.

Anthropogenic and biogenic tracers in fine aerosol based on seasonal distributions of dicarboxylic acids, sugars and related compounds at a rural background site in Central Europe

Water-soluble organic compounds in aerosols are considered as relevant indicators of atmospheric processes. Fine particulate matter (PM1) samples were collected at National Atmospheric Observatory Košetice (NAOK), a rural background site representative of Central Europe, from September 27, 2013 to August 9, 2014. The samples (n = 146) were analyzed for water-soluble dicarboxylic acids (hereafter referred to as diacids) and related compounds to identify their seasonal variations and origins. Based on the Positive Matrix Factorization (PMF) analysis, we identified 5 factors – 2 anthropogenic, 2 biogenic and 1 background factors.In winter, anthropogenic contributions dominated in total organic matter (OM). Typical tracers for the main winter anthropogenic factor 1, connected with biomass burning (BB), were anhydrosugars together with maleic (M), methylmaleic (mM) and methylsuccinic (iC5) acids. This BB factor accounted for 64.1 ± 14.3% of OM in winter (annual avg. 36.7 ± 27.4%). A secondary anthropogenic factor 2 was characterized by phthalic (Ph), terephthalic (tPh) and ketomalonic (kC3) acids, which we assigned to secondary combustion products. The contribution of anthropogenic factor 2 was at a similar level throughout the year (12.5 ± 10.1% in OM). Mainly in winter, although also in spring and autumn, was the characteristic formation of diacids by secondary aqueous phase reactions, typically accompanied by lower temperatures, global radiation and ozone (O3) concentrations, yet higher relative humidity (RH) and aerosol liquid water content (ALWC).In summer, contributions of biogenic origin dominated. Secondary organic aerosols (SOA) of biogenic origin were typically represented by malonic (C3), methylmalonic (iC4), 3-oxopropanoic (ωC3), 4-ketopimelic (kC7), 7-oxoheptanoic (ωC7), pimelic (C7) and suberic (C8) acids. The factor, named as Biogenic 1, was dominant in summer with a contribution of 40.3 ± 19.6% in OM, while in other seasons, its contribution was below 10%. This factor was mainly characterized by a relative summer increase in the concentrations of kC7 and ωC7 acids. The second biogenic factor 2, also significant in summer (36.8 ± 20.5%) and dominant in spring (34.9 ± 19.9%), was represented by primary sugars (fructose, galactose and sucrose), normal chain diacids (oxalic (C2) to azelaic (C9)) and their oxidative precursors (ωC3, 4-oxobutanoic (ωC4) and 5-oxopentanoic (ωC5) acids). The photochemical formation of SOA in the gas phase was characteristic mostly for the summer season, accompanied by higher temperatures, global radiation and O3 concentrations, and lower RH.Additionally, background factor was resolved, which represents compounds with no distinctive seasonal variation and can therefore be of both anthropogenic and biogenic origin and contained mainly less oxidized compounds (methylglyoxal (MeGly), glyoxal (Gly), glyoxylic acid (ωC2) and pyruvic acid (Pyr)).

Molecular composition and light-absorbing properties of organic aerosols from west-coast of tropical India

Tropical coastal regions may provide a unique feature to study the photooxidation of various organic aerosols and their climatic effects because of high humid atmosphere and intense solar radiation. However, knowledge about organic molecular composition and its light absorption properties remains concealed, particularly over tropical Indian regions. The present study is an investigation on water-soluble dicarboxylic acids, ω-oxoacids, pyruvic acid, α-dicarbonyls, brown carbon (BrC), and other chemical species in PM1.1 collected at a coastal urban location (Kochi) on the west coast of tropical India under distinct air masses. Molecular distribution of dicarboxylic acids was characterized by the predominance of oxalic acid (C2) in all the air masses followed by adipic (C6) or terephthalic (tPh) and phthalic (Ph) acids. On average, total diacids-C accounted for 5.03 ± 1.01 % of TC. Total diacid concentration showed strong linear relationships with organic (OC), elemental carbon (EC), and non-sea-salt potassium (nss-K+). Except for the northwest (NW) air mass period, the concentration of C2 diacid and its ratios (C2/total diacids, C2/ωC2, C2/Gly) showed a strong linear relationship with nss-SO42−. By combining all these results together with Pearson correlation analysis, the present study demonstrates that organic aerosols over the study region were predominantly produced by aqueous-phase oxidation of precursor compounds derived from biomass burning and combustion-related emissions. The mass absorption coefficient of BrC (babs-BrC-365nm) was strongly correlated with nss-K+, implying that biomass burning emissions are major sources of BrC. The absorption angstrom exponent (AÅE) values of water (methanol) extracts ranged from 3.20 to 3.83 (3.05–4.55) during the entire sampling period, indicating the substantial contribution of BrC chromophores to light absorption over the region. On average, BrC absorbs 10.6 ± 6.4 % and 22.4 ± 5.75 % of solar radiation compared to BC in water and methanol extracts, respectively, suggesting that BrC is a significant aerosol climate forcing agent over the west coast of tropical India.

Molecular characteristics of water-soluble dicarboxylic acids, ω-oxocarboxylic acids, pyruvic acid and α-dicarbonyls in the aerosols from the eastern North Pacific

Aerosol samples (n = 14), collected over the eastern North Pacific (ENP, 27–52°N and 150–172°W), were studied for dicarboxylic acids (hereafter diacids, C2-C10), ω-oxoacids, pyruvic acid, and α-dicarbonyls as well as water-soluble organic carbon (WSOC) and total nitrogen (WSTN). We found diacids as the most abundant compound class followed by ω-oxoacids and α-dicarbonyls. Molecular distributions of diacids were characterized by the predominance of oxalic (C2) (58%) acid followed by malonic (C3) (15%) and succinic (C4) (13.5%) acids. However, we found a predominance of C4 over C3 in five samples, where 4-oxobutanoic acid (ωC4) was the most abundant ω-oxoacid species (34.6% of its class). Moreover, a strong correlation (r2 = 0.72) was obtained between ωC4 and C4 in those samples, suggesting that high abundances of C4 are associated with sea-to-air emission of unsaturated fatty acids and their further photochemical processing. Good relationships between C2 and C3 (r2 = 0.88) and C3 and C4 (r2 = 0.79) in the marine aerosols further suggest that C2 is produced via photochemical degradation of C3 and C4 over the ENP. WSOC and WSTN showed higher abundances in the longitudinal transect of 165-172oW, where ω-oxoacids were abundantly detected. This study demonstrates that atmospheric levels of water-soluble organic aerosols in the ENP are largely regulated by the primary productivity followed by sea-to-air emissions of unsaturated fatty acids and isoprene and the subsequent photochemical oxidation.

Analysis of molecular species of phosphatidylcholine hydroperoxide in human native and copper-oxidized triglyceride-rich lipoproteins

The presence of water-soluble dicarboxylic acids in atmospheric aerosols has a significant influence on the regional radiative forcing through direct aerosol effect and cloud formation process. Fine aerosol (PM2.5) samples collected in central Alaska (Fairbanks: 64.51°N and 147.51°W) during summer of 2009 were measured for water-soluble diacids (C2–C12), oxoacids (C2–C9) and α-dicarbonyls (C2–C3) as well as elemental carbon (EC), organic carbon (OC) and water-soluble OC (WSOC) to assess their sources and formation processes. We found the predominance of oxalic acid (C2) followed by malonic (C3) and succinic acid (C4) in Alaskan aerosols. Higher C3/C4 diacid ratios (ave. 1.2) in Alaskan aerosols than those reported for fresh aerosols emitted from fossil fuel combustion (ave. 0.35) and biomass burning (0.51–0.66) suggest that organic aerosols in central Alaska were photochemically processed. The relatively high correlations of major diacids and related compounds with levoglucosan (r = 0.80–0.99) than those with 2-methylglyceric acid (r = 0.59–0.98) suggest that they were significantly produced from biomass burning emission. Strong correlations of C2 with normal-chain saturated diacids (C3-C9: r = 0.80–0.98), glyoxylic acid (ωC2: r = 0.95) and methylglyoxal (MeGly: r = 0.88), together with strong correlations of solar radiation with ratio of C2 to C2–C12 diacids (r = 0.83), ωC2 (r = 0.80) and MeGly (r = 0.82) suggest that oxalic acid in PM2.5 aerosol was produced by the photooxidation of higher homologous diacids, glyoxylic acid and methylglyoxal in the atmosphere of central Alaska. These results reveal that photochemical processing of organic precursors mainly produced from biomass burning control the water-soluble organic chemical composition of fine aerosols in central Alaska.

Measuring hygroscopicity of internally mixed NaNO3 and glutaric acid particles by vacuum FTIR.

Sodium nitrate as an important inorganic component can be chemically formed from the reactions of nitrogen oxides and nitric acid (HNO3) with sea salt in atmosphere. Organic acids contribute a significant fraction of photochemical formed secondary organics that can condense on the preexisting nitrate-containing particles. Atmospheric particles often include a complex mixture of nitrate and secondary organic materials accumulated within the same individual particles. Here we studied the hygroscopicity of aerosol particles composed of sodium nitrate and glutaric acid (GA) by using a pulsed RH controlling system and a rapid scan vacuum FTIR spectrometer (PRHCS-RSVFTIR). The water content in the particles and efflorescence ratios of both NaNO3 and GA at ambient relative humidity (RH) as a function of time were obtained from the rapid-scan infrared spectra with a sub-second time resolution. Our study showed that both NaNO3 and GA crystallized at 44.1% RH during two different RH control processes (stepwise and pulsed processes). It was found that the addition of GA could suppress the efflorescence of NaNO3 during the dehumidifying process. In addition, the mixed NaNO3/GA particles release HNO3 during the dehumidifying and humidifying cycles. These findings are important in further understanding the role of interactions between water-soluble dicarboxylic acids and nitrates on hygroscopicity and environmental effects of atmospheric particles.

High Loadings of Water-Soluble Oxalic Acid and Related Compounds in PM2.5 Aerosols in Eastern Central India: Influence of Biomass Burning and Photochemical Processing

ABSTRACT Water-soluble organic compounds are important constituents of atmospheric aerosols and have been recognized as unique fingerprints to identify atmospheric processes. Fine aerosol samples (PM2.5) were collected at Ambikapur (23.1°N and 83.2°E) in eastern central India from March to June 2017. The samples were analyzed for water-soluble dicarboxylic acids (C2–C12), glyoxylic acid (ωC2), glyoxal (Gly), methylglyoxal (MeGly), organic carbon (OC), elemental carbon (EC) and water-soluble OC (WSOC). Oxalic acid (C2) was detected as the most abundant species, followed by succinic (C4) and malonic (C3) acids. Temporal variation in concentrations of C2 diacid and related compounds was pronounced from early to late April when biomass burning (BB) was dominant in eastern central India. Strong positive correlations of C2 diacid and related compounds with levoglucosan (r = 0.83–0.99) further demonstrate that organic aerosols (OAs) were affected by BB in eastern central India. Strong positive correlations of C2 with saturated diacids (C3–C9: r = 0.78–0.97), ωC2 (r = 0.98), Gly (r = 0.96) and MeGly (r = 0.84) suggest that their sources and formation processes were similar and oxalic acid might be produced via the photochemical degradation of precursor compounds. The relatively high ratios of WSOC to OC (avg. 0.69) and C3 to C4 diacid (avg. 0.95) suggest that water-soluble OAs were photochemically processed during the campaign. The total water-soluble organic compounds detected in Ambikapur PM2.5 samples accounted for an average of 1.9% (1.1–3.1%) of OC. Our results demonstrate that BB and photochemical processing caused high levels of water-soluble organic compounds over eastern central India.

Dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls in fine aerosols over central Alaska: Implications for sources and atmospheric processes

The presence of water-soluble dicarboxylic acids in atmospheric aerosols has a significant influence on the regional radiative forcing through direct aerosol effect and cloud formation process. Fine aerosol (PM2.5) samples collected in central Alaska (Fairbanks: 64.51°N and 147.51°W) during summer of 2009 were measured for water-soluble diacids (C2–C12), oxoacids (C2–C9) and α-dicarbonyls (C2–C3) as well as elemental carbon (EC), organic carbon (OC) and water-soluble OC (WSOC) to assess their sources and formation processes. We found the predominance of oxalic acid (C2) followed by malonic (C3) and succinic acid (C4) in Alaskan aerosols. Higher C3/C4 diacid ratios (ave. 1.2) in Alaskan aerosols than those reported for fresh aerosols emitted from fossil fuel combustion (ave. 0.35) and biomass burning (0.51–0.66) suggest that organic aerosols in central Alaska were photochemically processed. The relatively high correlations of major diacids and related compounds with levoglucosan (r=0.80–0.99) than those with 2-methylglyceric acid (r=0.59–0.98) suggest that they were significantly produced from biomass burning emission. Strong correlations of C2 with normal-chain saturated diacids (C3-C9: r=0.80–0.98), glyoxylic acid (ωC2: r=0.95) and methylglyoxal (MeGly: r=0.88), together with strong correlations of solar radiation with ratio of C2 to C2–C12 diacids (r=0.83), ωC2 (r=0.80) and MeGly (r=0.82) suggest that oxalic acid in PM2.5 aerosol was produced by the photooxidation of higher homologous diacids, glyoxylic acid and methylglyoxal in the atmosphere of central Alaska. These results reveal that photochemical processing of organic precursors mainly produced from biomass burning control the water-soluble organic chemical composition of fine aerosols in central Alaska.

Long-term (2001\u20132013) observations of water-soluble dicarboxylic acids and related compounds over the western North Pacific: trends, seasonality and source apportionment

To better understand the impact of East Asian pollutants on the molecular composition of marine organic aerosols, we conducted long-term (2001–2013) observations of water-soluble dicarboxylic acids and related compounds in total suspended particulate samples collected at Chichijima Island in the western North Pacific (WNP). Seasonal variations of all the diacids and related compounds showed maxima in winter and spring and minima in summer, except for azelaic acid (C9), which maximized in summer to autumn. The overall annual concentrations of the total diacids, ω-oxoacids and α-dicarbonyls showed an increase during 2001–2013. We found a significant (p < 0.05) decadal increase in the inter-annual trends of pyruvic and glyoxylic (p > 0.05) acids, and methylglyoxal (MeGly). In contrast, phthalic acid (p < 0.05) and glyoxal (Gly) showed a decrease in their trends. We also found a significant decrease in the trend of the Gly/MeGly mass ratios. These results demonstrate that the enhanced concentrations of diacids over the WNP are majorly attributed to the aqueous-phase photooxidation of biogenic volatile organic compounds from East Asia followed by long-range atmospheric transport. Further, positive matrix factorization analysis showed a biogenic photochemical contribution (42%) was the dominant source of oxalic acid in the WNP.

Spatio-temporal distributions of dicarboxylic acids, ω-oxocarboxylic acids, pyruvic acid, α-dicarbonyls and fatty acids in the marine aerosols from the North and South Pacific

Aerosol samples (TSP) were collected during a cruise in the North (3°05′N–34°02′N) and South (6°59′S–25°46′S) Pacific to investigate the spatio-temporal distributions of water-soluble dicarboxylic acids and related compounds. The molecular distributions of diacids were characterized by the predominance of oxalic (C2) acid followed by malonic (C3) and then succinic (C4) acid. However, we found a predominance of C4 over C3 in the aerosol sample that was collected in the western North Pacific Rim with a heavy influence from continental air masses. Atmospheric abundances of short chain diacids (C2–C4) are 2–3 times higher in the North Pacific than in the South Pacific. During the cruise, abundances of C2 in the western North Pacific are 5 times higher than those in the rest of the samples collected. Moreover, the aerosol samples collected in the western North Pacific demonstrated that glyoxylic (ωC2) acid and methylglyoxal (MeGly) were dominant together with C2. We found a strong correlation between C2 and ωC2 (r=0.87) and C2 and MeGly (r=0.97) in the western North Pacific aerosols but the correlations are significantly weak in the samples from the central North Pacific and Southern Ocean. Diacids were found to account for 1.6 to 14% of organic carbon with higher values in the western North Pacific. These results, together with 7-day backward air mass trajectories, indicate that ωC2 and MeGly are both originated from the photochemical oxidation of continent-derived organic precursors including isoprene, which can serve as precursors for the production of C2 during long-range atmospheric transport.

Aircraft observations of water-soluble dicarboxylic acids in the aerosols over China

Abstract. Vertical profiles of dicarboxylic acids, related organic compounds and secondary organic aerosol (SOA) tracer compounds in particle phase have not yet been simultaneously explored in East Asia, although there is growing evidence that aqueous-phase oxidation of volatile organic compounds may be responsible for the elevated organic aerosols (OA) in the troposphere. Here, we found consistently good correlation of oxalic acid, the most abundant individual organic compounds in aerosols globally, with its precursors as well as biogenic-derived SOA compounds in Chinese tropospheric aerosols by aircraft measurements. Anthropogenically derived dicarboxylic acids (i.e., C5 and C6 diacids) at high altitudes were 4–20 times higher than those from surface measurements and even occasionally dominant over oxalic acid at altitudes higher than 2 km, which is in contrast to the predominance of oxalic acid previously reported globally including the tropospheric and surface aerosols. This indicates an enhancement of tropospheric SOA formation from anthropogenic precursors. Furthermore, oxalic acid-to-sulfate ratio maximized at altitudes of ∼ 2 km, explaining aqueous-phase SOA production that was supported by good correlations with predicted liquid water content, organic carbon and biogenic SOA tracers. These results demonstrate that elevated oxalic acid and related SOA compounds from both the anthropogenic and biogenic sources may substantially contribute to tropospheric OA burden over polluted regions of China, implying aerosol-associated climate effects and intercontinental transport.

Investigation of the tracers for plastic-enriched waste burning aerosols

To better identify the tracers for open-waste burning (OWB) aerosols, we have conducted aerosol sampling at 2 landfill sites, i.e., Okhla and Bhalswa in New Delhi. The metals such as, As, Cd, Sb and Sn, which have been observed almost negligible in remote aerosols, are found abundantly in these OWB aerosol samples (n=26), i.e., 60±65, 41±53, 537±847 and 1325±1218ngm−3, respectively. Samples (n=20) collected at urban locations in New Delhi, i.e., at Employees' State Insurance (ESI) hospital and National Physical Laboratory (NPL) also show high abundances of these metals in the particles. Filter samples are also analyzed for water-soluble dicarboxylic acids (C2–C12) and related compounds (oxocarboxylic acids and α-dicarbonyls). Terephthalic acid (tPh) was found to account for more than 77% of total diacids determined in OWB aerosols. However, such a high abundance of tPh is not observed in aerosols collected at urban sites. Instead, phthalic acid (Ph) was found as the third/fourth most abundant diacid (∼3%) following C2 (>70%) and C4 (>12%) in these waste burning influenced urban aerosols. A possible secondary formation pathway of Ph by photo-degradation of phthalate ester (di-2-ethylhexyl phthalate) in plastic-waste burning aerosol is suggested. Ionic composition of OWB aerosols showed that Cl− is the most abundant ion (40±8% of total ions determined). The correlation studies of the potential metals with the organic tracers of garbage burning, i.e., phthalic, isophthalic and terephthalic acids show that especially Sn can be used as marker for tracing the plastic-enriched waste burning aerosols.

Diurnal and temporal variations of water-soluble dicarboxylic acids and related compounds in aerosols from the northern vicinity of Beijing: Implication for photochemical aging during atmospheric transport

Aerosol samples were collected in autumn 2007 on day- and nighttime basis in the northern receptor site of Beijing, China. The samples were analyzed for total carbon (TC) and water-soluble dicarboxylic acids (C2–C12), oxocarboxylic acids (C2–C9), glyoxal and methylglyoxal to better understand the photochemical aging of organic aerosols in the vicinity of Beijing. Concentrations of TC are 50% greater in daytime when winds come from Beijing than in nighttime when winds come from the northern forest areas. Most diacids showed higher concentrations in daytime, suggesting that the organics emitted from the urban Beijing and delivered to the northern vicinity in daytime are subjected to photo-oxidation to result in diacids. However, oxalic acid (C2), which is the most abundant diacid followed by C3 or C4, became on average 30% more abundant in nighttime together with azelaic, ω-oxooctanoic and ω-oxononanoic acids, which are specific oxidation products of biogenic unsaturated fatty acids. Methylglyoxal, an oxidation product of isoprene and a precursor of oxalic acid, also became 29% more abundant in nighttime. Based on a positive correlation between C2 and glyoxylic acid (ωC2) in nighttime when relative humidity significantly enhanced, we propose a nighttime aqueous phase production of C2 via the oxidation of ωC2. We found an increase in the contribution of diacids to TC by 3 folds during consecutive clear days. This study demonstrates that diacids and related compounds are largely produced in the northern vicinity of Beijing via photochemical processing of organic precursors emitted from urban center and forest areas.

Seasonal distributions and sources of low molecular weight dicarboxylic acids, ω-oxocarboxylic acids, pyruvic acid, α-dicarbonyls and fatty acids in ambient aerosols from subtropical Okinawa in the western Pacific Rim

Environmental context Water-soluble dicarboxylic acids and related compounds are ubiquitous in atmospheric aerosols. They are abundantly emitted from Asian countries and transported to the Pacific Ocean. During the long-range transport, photochemical processing modifies organic aerosols. We conducted a 1-year observation of diacids and related compounds at Okinawa Island, an outflow region of the Asian Continent, to clarify their sources and photochemical aging. Abstract Ambient aerosol samples were collected for 1 year at Okinawa Island, Japan, and were analysed for water-soluble dicarboxylic acids, oxoacids, α-dicarbonyls and fatty acids to better understand biogenic v. anthropogenic sources and the formation–transformation of organic aerosols during long-range atmospheric transport. Here, we report seasonal variations of diacids and related compounds in Okinawa. We found a predominance of oxalic acid (C2) followed by malonic (C3) and succinic (C4) acid. Total diacids and oxoacids maximised in spring when air masses originated from the Asian Continent with westerly winds. In contrast, phthalic acid (Ph), a tracer of anthropogenic sources, peaked in winter. We found an increased C3/C4 ratio in summer, suggesting an enhanced photochemical aging of organic aerosols. The average ratio of total diacid-C/total carbon (TC) (5.4%) is higher than that (3.1%) from the East China Sea, suggesting that Okinawa aerosols are more aged than East Asian aerosols but less aged compared to those from the remote Pacific including tropics (8.8%). Biogenic short-chain fatty acids and azelaic acid (C9), the latter is a specific oxidation product of unsaturated fatty acids, maximised in summer, whereas higher plant-derived long-chain fatty acids maximised in spring. This study demonstrates that the ambient aerosols in Okinawa are strongly influenced by the Asian outflow in winter and spring and by biogenic organic matter in summer and spring. Enhanced contribution of oxalic acid to aerosol TC in spring suggests that Okinawa organic aerosols are mainly produced in East Asia and photochemically transformed during the transport.

High abundances of water-soluble dicarboxylic acids, ketocarboxylic acids and α-dicarbonyls in the mountaintop aerosols over the North China Plain during wheat burning season

Abstract. Aerosol (TSP) samples were collected at the summit of Mount Tai (elevation: 1534 m a.s.l., 36.25° N, 117.10° E) located in the North China Plain using a high-volume air sampler and pre-combusted quartz filters. Sampling was conducted on day/night or 3 h basis in the period from 29 May to 28 June 2006 during the field burning of wheat straw residue and the post-burning season. The filter samples were analyzed for low-molecular-weight dicarboxylic acids, ketoacids and α-dicarbonyls using capillary gas chromatography (GC) and GC-MS employing water extraction and butyl ester derivatization. Molecular distributions of dicarboxylic acids (C2-C11, 220–6070 ng m−3) were characterized by a predominance of oxalic (C2) acid (105–3920 ng m−3) followed by succinic (C4) or malonic (C3) acid. Unsaturated aliphatic diacids, including maleic (M), isomaleic (iM) and fumaric (F) acids, were also detected together with aromatic diacids (phthalic, isophthalic and terephthalic acids). ω-oxocarboxylic acids (C2-C9, 24–610 ng m−3) were detected as the second most abundant compound class with the predominance of glyoxylic acid (11–360 ng m−3), followed by α-ketoacid (pyruvic acid, 3–140 ng m−3) and α-dicarbonyls (glyoxal, 1–230 ng m−3 and methylglyoxal, 2–120 ng m−3). We found that these levels (&gt;6000 ng m−3 for diacids) are several times higher than those reported in Chinese megacities at ground levels. The concentrations of diacids increased from late May to early June, showing a maximum on 7 June, and then significantly decreased during the period 8–11 June, when the wind direction shifted from southerly to northerly. Similar temporal trends were found for ketocarboxylic acids and α-dicarbonyls as well as total carbon (TC) and water-soluble organic carbon (WSOC). The temporal variations of water-soluble organics were interpreted by the direct emission from the field burning of agricultural wastes (wheat straw) in the North China Plain and the subsequent photochemical oxidation of volatile and semi-volatile organic precursors emitted from field burning as well as dark ozonolysis of volatile organic compounds and other organics, accretion reactions and oxidation of nonvolatile organics such as unsaturated fatty acids. This study demonstrates that the field burning of agricultural wastes in early summer strongly influenced the air quality of the free troposphere over the North China Plain.

Molecular composition of dicarboxylic acids, ketocarboxylic acids, α-dicarbonyls and fatty acids in atmospheric aerosols from Tanzania, East Africa during wet and dry seasons

Abstract. Atmospheric aerosol samples of PM2.5 and PM10 were collected during the wet and dry seasons in 2011 from a rural site in Tanzania and analysed for water-soluble dicarboxylic acids, ketocarboxylic acids, α-dicarbonyls, and fatty acids using a gas chromatography/flame ionization detector (GC/FID) and GC/mass spectrometry. Here we report the molecular composition and sources of diacids and related compounds for wet and dry seasons. Oxalic acid (C2) was found as the most abundant diacid species followed by succinic and/or malonic acids whereas glyoxylic acid and glyoxal were the dominant ketoacid and α-dicarbonyl, respectively in both seasons in PM2.5 and PM10. Mean concentration of C2 in PM2.5 (121 ± 47 ng m−3) was lower in wet season than dry season (258 ± 69 ng m−3). Similarly, PM10 samples showed lower concentration of C2 (169 ± 42 ng m−3) in wet season than dry season (292 ± 165 ng m−3). Relative abundances of C2 in total diacids were 65% and 67% in PM2.5 and 65% and 64% in PM10 in the wet and dry seasons, respectively. Total concentrations of diacids (289–362 ng m−3), ketoacids (37.8–53.7 ng m−3), and α-dicarbonyls (5.7–7.8 ng m−3) in Tanzania are higher than those reported at a rural background site in Nylsvley (South Africa) but comparable or lower than those reported from sites in Asia and Europe. Diacids and ketoacids were found to be present mainly in PM2.5 in both seasons (total α-dicarbonyls in the dry season), suggesting a production of organic acids from pyrogenic sources and photochemical oxidations. Averaged contributions of total diacids to aerosol total carbon were 1.4% in PM2.5 and 2.1% in PM10 during wet season and 3.3% in PM2.5 and 3.9% in PM10 during dry season whereas those to water-soluble organic carbon were 2.2% and 4.7% in PM2.5 during wet season and 3.1% and 5.8% in PM10 during dry season. The higher ratios in dry season suggest an enhanced photochemical oxidation of organic precursors probably via heterogeneous reactions on aerosols under strong solar radiation. Strong positive correlations were found among diacids and related compounds as well as good relations to source tracers in both seasons, suggesting a mixed source from natural biogenic emissions, biomass burning, biofuel combustion, and photochemical production.

Dicarboxylic acids, ketocarboxylic acids and glyoxal in the marine aerosols collected during a round-the-world cruise

This study investigated spatial distributions of water-soluble dicarboxylic acids and related compounds in the marine aerosols collected at low- to mid-latitudes in the Northern Hemisphere for a better understanding of the photochemical aging of organic aerosols during long-range transport. Their molecular distributions were characterized by the predominance of oxalic acid (C2) followed by malonic (C3) and succinic (C4) acids, except for one sample (QFF114, C2>C4>C3) that was collected in the western North Pacific with a heavy influence of biomass burning. Concentration ranges of diacids, ketoacids (including glyoxylic acid and pyruvic acid), and glyoxal were 17–718ngm−3 (average 218ngm−3), 0.40–72ngm−3 (23ngm−3), and 0.16–19ngm−3 (3.3ngm−3), which account for 3.6–23% (14%), 0.09–2.3% (1.3%), and 0.04–0.45% (0.19%) of organic carbon (OC) in the marine aerosols, respectively. Positive correlations were observed between OC and diacids/ketoacids. Positive correlations were also found between biogenic secondary organic aerosol (SOA) tracers (e.g., 2-methylglyceric acid) and diacids/ketoacids, suggesting a significant contribution of biogenic secondary source. The spatial distributions of diacids exhibited higher loadings over the coastal/tropical regions than the open oceans, which are similar to those of the concentration ratios of malonic/succinic (C3/C4) and adipic/azelaic (C6/C9), indicating a more significant influence of anthropogenic sources over the coastal regions than the remote oceans. However, the concentration ratios of oxalic acid to levoglucosan, a biomass-burning tracer, and to C29n-alkane, a tracer for terrestrial biogenic emission showed higher values over the open oceans than the coastal regions, suggesting a continuous production of oxalic acid during long-range atmospheric transport. This study indicates that the long-range transport of primary and secondary aerosols of continental origin and photo-oxidation/aerosol aging are important factors controlling the organic chemical composition of aerosol particles in the marine atmosphere.

Seasonal variations of water-soluble organic carbon, dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls in Central Himalayan aerosols

Abstract. Aerosol samples were collected from a high elevation mountain site (Nainital, India; 1958 m a.s.l.) in the central Himalayas, a location that provides an isolated platform above the planetary boundary layer to better understand the composition of the remote continental troposphere. The samples were analyzed for water-soluble dicarboxylic acids (C2-C12) and related compounds (ketocarboxylic acids and α-dicarbonyls), as well as organic carbon, elemental carbon and water soluble organic carbon. The contributions of total dicarboxylic acids to total aerosol carbon during wintertime were 1.7% and 1.8%, for day and night, respectively whereas they were significantly smaller during summer. Molecular distributions of diacids revealed that oxalic (C2) acid was the most abundant species followed by succinic (C4) and malonic (C3) acids. The average concentrations of total diacids (433±108 ng m−3), ketoacids (48±23 ng m−3), and α-dicarbonyls (9±4 ng m−3) were similar to those from large Asian cities such as Tokyo, Beijing and Hong Kong. During summer most of the organic species were several times more abundant than in winter. Phthalic acid, which originates from oxidation of polycyclic aromatic hydrocarbons such as naphthalene, was found to be 7 times higher in summer than winter. This feature has not been reported before in atmospheric aerosols. Based on molecular distributions and air mass backward trajectories, we conclude that dicarboxylic acids and related compounds in Himalayan aerosols are derived from anthropogenic activities in the highly populated Indo-Gangetic plain areas.

Enhanced concentrations of citric acid in spring aerosols collected at the Gosan background site in East Asia

In order to investigate water-soluble dicarboxylic acids and related compounds in the aerosol samples under the Asian continent outflow, total suspended particle (TSP) samples (n = 32) were collected at the Gosan site in Jeju Island over 2–5 days integration during 23 March–1 June 2007 and 16–24 April 2008. The samples were analyzed for water-soluble dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls using a capillary gas chromatography technique. We found elevated concentrations of atmospheric citric acid (range: 20–320 ng m−3) in the TSP samples during mid- to late April of 2007 and 2008. To specify the sources of citric acid, dicarboxylic acids and related compounds were measured in the pollen sample collected at the Gosan site (Pollen_Gosan), authentic pollen samples from Japanese cedar (Cryptomeria) (Pollen_cedar) and Japanese cypress (Chamaecyparis obtusa) (Pollen_cypress), and tangerine fruit produced from Jeju Island. Citric acid (2790 ng in unit mg of pollen mass) was found as most abundant species in the Pollen_Gosan, followed by oxalic acid (2390 ng mg−1). Although citric acid was not detected in the Pollen_cedar and Pollen_cypress as major species, it was found as a dominant species in the tangerine juice while malic acid was detected as major species in the tangerine peel, followed by oxalic and citric acids. Since Japanese cedar trees are planted around tangerine farms to prevent strong winds from the Pacific Ocean, citric acid that may be directly emitted from tangerine is likely adsorbed on pollens emitted from Japanese cedar and then transported to the Gosan site. Much lower malic/citric acid ratios obtained under cloudy condition than clear condition suggest that malic acid may rapidly decompose to lower molecular weight compounds such as oxalic and malonic acids (<C4) via aqueous phase reaction in cloud during the atmospheric transport.