This review aims to update our understanding on molecular distributions of water-soluble dicarboxylic acids and related compounds in atmospheric aerosols with a focus on their geographical ...variability, size distribution, sources and formation pathways. In general, molecular distributions of diacids in aerosols from the continental sites and over the open ocean waters are often characterized by the predominance of oxalic acid (C2) followed by malonic acid (C3) and/or succinic acid (C4), while those sampled over the polar regions often follow the order of C4≥C2 and C3. The most abundant and ubiquitous diacid is oxalic acid, which is principally formed via atmospheric oxidation of its higher homologues of long chain diacids and other pollution-derived organic precursors (e.g., olefins and aromatic hydrocarbons). However, its occurrence in marine aerosols is mainly due to the transport from continental outflows (e.g., East Asian outflow during winter/spring to the North Pacific) and/or governed by photochemical/aqueous phase oxidation of biogenic unsaturated fatty acids (e.g., oleic acid) and isoprene emitted from the productive open ocean waters. The long-range atmospheric transport of pollutants from mid latitudes to the Arctic in dark winter facilitates to accumulate the reactants prior to their intense photochemical oxidation during springtime polar sunrise. Furthermore, the relative abundances of C2 in total diacid mass showed similar temporal trends with downward solar irradiation and ambient temperatures, suggesting the significance of atmospheric photochemical oxidation processing. Compound-specific isotopic analyses of oxalic acid showed the highest δ13C among diacids whereas azelaic acid showed the lowest value, corroborating the significance of atmospheric aging of oxalic acid. On the other hand, other diacids gave intermediate values between these two diacids, suggesting that aging of oxalic acid is associated with 13C enrichment.
Low molecular weight monocarboxylic acids (LMW monoacids, C1–C10) are the most abundant gaseous organic compound class in the atmosphere. Formic or acetic acid is the dominant volatile organic ...compound (VOC) in Earth’s atmosphere. They can largely contribute to rainwater acidity, especially in the tropical forest, and react with alkaline metals, ammonia, and amines, contributing to new particle formation and secondary organic aerosol production. Gaseous and particulate LMW monoacids were abundantly reported in China. They can be directly emitted from fossil fuel combustion and biomass burring; however, the secondary formation is more important than primary emissions via the photochemical oxidation of anthropogenic and biogenic VOCs. In this paper, we review the distributions of LMW monoacids from urban, mountain, and marine sites as well as from rainwater and alpine snow samples and discuss their sources and formation mechanisms in the atmosphere. We also discuss their importance as cloud condensation nuclei (CCN) and provide future perspectives of LMW monoacids study in the warming world.
Primary biological aerosol particles (PBAPs) play an important role in affecting atmospheric physical and chemical properties. Aerosol samples were collected at Cape Hedo, Okinawa Island, Japan, from ...October 2009 to February 2012 and analyzed for five primary saccharides and four sugar alcohols as PBAP tracers. We detected high levels of sucrose in spring when blossoming of plants happens and prolifically emits pollen to the air. Concentrations of glucose, fructose, and trehalose showed levels higher than the other saccharides in spring in 2010. In comparison, primary saccharide levels were mutually comparable in spring, summer, and autumn in 2011, indicating the interannual variability of their local production in subtropical forests, which is driven by local temperature and radiation. High trehalose events were found to be associated with Asian dust outflows, indicating that Asian dust also contributes to PBAPs at Okinawa. Sugar alcohols peaked in summer and correlated with local precipitation and temperature, indicating high microbial activities. Positive matrix factorization analysis confirmed that the PBAPs are mainly derived from local vegetation, pollen, and fungal spores. A higher contribution of PBAP tracers to water‐soluble organic carbon (WSOC) was found in summer (14.9%). The annual mean ambient loadings of fungal spores and PBAPs were estimated as 0.49 µg m−3 and 4.12 µg m−3, respectively, using the tracer method. We report, for the first time, year‐round biomarkers of PBAP and soil dust and their contributions to WSOC in the subtropical outflow region of the Asian continent.
Key Points
PBAPs in Okinawa aerosols are largely affected by sources from local forest
PBAP emissions from forest contribute largely to WSOC in aerosols
Ambient fungal spore and PBAP loadings at Okinawa are estimated
High levels of carbonaceous aerosol exist over South Asia, the area adjacent to the Himalayas and Tibetan Plateau. Little is known about if they can be transported across the Himalayas, and as far ...inland as the Tibetan Plateau. As important constituents of aerosols, organic acids have been recognized as unique fingerprints to identify the atmospheric process. Here we measured dicarboxylic acids and related compounds in aerosols on the northern slope of Mt. Everest (Qomolangma, 4276 m a.s.l.). Strong positive correlations were observed for dicarboxylic acids with biomass burning tracers, levoglucosan and K(+), demonstrating that this area was evidently affected by biomass burning. The seasonal variation pattern of dicarboxylic acids is consistent with OC and EC, being characterized by a pronounced maximum in the pre-monsoon season. Molecular distributions of dicarboxylic acids and related compounds (malonic acid/succinic acid, maleic acid/fumaric acid) further support this finding. We suggest that the local meteorological conditions and regional atmospheric flow process could facilitate the penetration of the carbonaceous aerosols from South Asia throughout the Himalayas. With the consideration of the darkening force of carbonaceous aerosols, our finding has important implication for this climate-sensitive area, where the glacier melting supplies water for billions of people downstream.
A lack of consensus on the distributions and formation pathways of secondary organic aerosols (SOA) over oceanic regions downwind of pollution sources limits our ability to assess their climate ...impact globally. As a case study, we report here on water-soluble SOA components such as dicarboxylic acids, oxocarboxylic acids, and α-dicarbonyls in the continental outflows from the Indo-Gangetic Plain (IGP) and Southeast Asia (SEA) to the Bay of Bengal. Oxalic acid (C2) is the dominant species followed by succinic (C4) and glyoxylic acids (ωC2) in the outflow. Nonsea-salt SO4 2– also dominates (∼70%) total water-soluble inorganic constituents and correlates well with aerosol liquid water content (LWC) and C2, indicating their production through aqueous phase photochemical reactions. Furthermore, mass ratios of dicarboxylic acids (C2/C4, C2/ωC2), and their relative abundances in water-soluble organic carbon and total organic carbon are quite similar between the two continental (IGP and SEA) outflows, indicating the formation of SOA through aqueous phase photochemical reactions in LWC-enriched aerosols, largely controlled by anthropogenic SO4 2–.
We investigated organic molecular compositions of summertime aerosols collected at the summit of Mt. Fuji (3776 m a.s.l.) in July–August 2009. More than 120 organic species were identified using ...GC/MS. Concentrations of both primary and secondary organic aerosol (SOA) tracers in whole-day samples were 4–20 times higher than those in nighttime samples, suggesting that valley breeze is an efficient mechanism to uplift the aerosols and precursors from the ground surface to mountaintop in daytime. Using a tracer-based method, we estimated the concentrations of secondary organic carbon (SOC) derived from isoprene, α/β-pinene, and β-caryophyllene to be 2.2–51.2 ngC m–3 in nighttime and 227–1120 ngC m–3 during whole-day. These biogenic SOCs correspond to 0.80–31.9% and 26.8–57.4% of aerosol organic carbon in nighttime and whole-day samples, respectively. This study demonstrates that biogenic SOA, which is controlled by the valley breeze, is a significant fraction of free tropospheric aerosols over Mt. Fuji in summer.
Organic molecular compositions of marine aerosol samples, collected at low latitudes to midlatitudes in the Northern Hemisphere during a round‐the‐world cruise, were studied using gas ...chromatography/mass spectrometry. More than 140 organic species were detected in the samples and were grouped into different compound classes based on the functionality and sources. The concentrations of total quantified organics ranged from 0.94 to 111 ng m−3 (average of 34 ng m−3). Biogenic secondary organic aerosol (SOA) tracers from the oxidation of isoprene (e.g., 2‐methyltetrols), α/β‐pinene (e.g., pinonic and pinic acids), and β‐caryophyllene (β‐caryophyllinic acid) were detected in all the samples. Their total concentrations ranged from 0.19 to 27 ng m−3, which account for 0.48–29% of the total identified organics and 0.05–1.5% of organic carbon in the marine aerosols. The spatial distributions of biogenic SOA tracers exhibited higher loadings over the coastal/tropical regions than the open oceans. In marine aerosols collected over the North Pacific and North Atlantic, the contributions of marine natural emissions (22–33%) were higher than those in the coastal regions (4–14%). Over the tropical regions, atmospheric oxidation products can account for 47–59% of the total organics, with biomass burning emissions of only 1–2%. However, over the western North Pacific, fossil fuel combustion (26%), atmospheric oxidation products (25%), and biomass burning (24%) were the main sources. This study indicates that long‐range atmospheric transport of continental aerosols and sea‐to‐air emission of marine organics, as well as atmospheric oxidation and/or photochemical aging, are important factors controlling the chemical composition of organic aerosols in the marine atmosphere.
Key Points
Marine organic aerosols were investigated at a molecular level
Direct evidances were obtained for biogenic SOA tracers in the marine aerosols
The source strengths are apportioned based on the identified organics
Abstract
To investigate the applicability of compound specific stable carbon isotope ratios (δ
13
C) of organics in assessment of their photochemical aging in the atmosphere, batch UV irradiation ...experiments were conducted on two ambient (anthropogenic and biogenic) aerosol samples in aqueous phase for 0.5–120 h. The irradiated samples were analyzed for δ
13
C of diacids, glyoxylic acid (ωC
2
) and glyoxal. δ
13
C of diacids and related compounds became larger with irradiation time (i.e., aging), except for few cases. In general, δ
13
C of C
2
-C
4
diacids showed an increasing trend with decreasing chain length. Based on δ
13
C of diacids and related compounds and their relations to their concentrations, we found that C
2
and C
3
are enriched with
13
C during the photochemical decomposition and production from their higher homologues and oxoacids. Photochemical breakdown of higher (≥C
3
) to lower diacids is also important in the enrichment of
13
C in C
3
-C
9
diacids whereas their production from primary precursors causes depletion of
13
C. In case of ωC
2
and glyoxal, their photochemical production and further oxidation to highly oxygenated compounds both cause the enrichment of
13
C. This study reveals that δ
13
C of diacids and related compounds can be used as a proxy to trace the aging of organic aerosols during long-range atmospheric transport.
Stable carbon (δ13C) and nitrogen (δ15N) isotope ratios were measured for total carbon (TC) and nitrogen (TN), respectively, in aerosol (TSP) samples collected at Cape Hedo, Okinawa, an outflow ...region of Asian pollutants, during 2009–2010. The averaged δ13C and δ15N ratios are −22.2‰ and +12.5‰, respectively. The δ13C values are similar in both spring (−22.5‰) and winter (−22.5‰), suggesting the similar sources and/or source regions. We found that δ13C from Okinawa aerosols are ca. 2‰ higher than those reported from Chinese megacities probably due to photochemical aging of organic aerosols. A strong correlation (r = 0.81) was found between nss-Ca and TSP, suggesting that springtime aerosols are influenced from Asian dusts. However, carbonates in the Asian dusts were titrated with acidic species such as sulfuric acid and oxalic acid during atmospheric transport although two samples suggested the presence of remaining carbonate. No correlations were found between δ13C and tracer compounds (levoglucosan, elemental carbon, oxalic acid, and Na+). During winter and spring, coal burning is significant source in China. Based on isotopic mass balance, contribution of coal burning origin particles to total aerosol carbon was estimated as ca. 97% in winter, which is probably associated with the high emissions in China. Contribution of NO3− to TN was on average 45% whereas that of NH4+ was 18%. These results suggest that vehicular exhaust is an important source of TN in Okinawa aerosols. Concentration of water-soluble organic nitrogen (WSON) is higher in summer, suggesting that WSON is more emitted from the ocean in warmer season whereas inorganic nitrogen is more emitted in winter and spring from pollution sources in the Asian continent.
•We measured stable carbon and nitrogen isotope ratios in Okinawa aerosols.•We found serious transport of Asian dust and pollutants in winter and spring.•δ13C of Okinawa aerosol are ca. 2‰ higher than those of Chinese megacities.•Organic aerosols may be photochemically more aged during atmospheric transport.•We found significant contribution of Ca in spring but carbonate was already titrated.
The widespread haze pollution over South Asia typically occurs in winter, affecting the abundance of organic aerosols (OA) over the Arabian Sea due to prevailing meteorology. We determined the ...concentrations of biomass burning (BB) derived anhydrosugars (levoglucosan: Lev, galactosan: Gal, and mannosan: Man), sugars (glucose, fructose, sucrose, and trehalose) and sugar alcohols (arabitol, mannitol, erythritol, and inositol) over the Arabian Sea during a winter cruise (6–24 December 2018). Molecular distributions revealed predominance of levoglucosan or sucrose. Besides, levoglucosan strongly correlated with mannosan, galactosan, sugar alcohols and elemental carbon, emphasizing their BB-origin. Backward air mass trajectories intercepted by the satellite-based fire counts over the Indo-Gangetic Plain together with relationship between stable carbon isotopic composition of TC (δ13CTC) and levoglucosan-C to organic carbon (%), confirmed the impact of BB-derived OA. A comparison of Lev/Man (av. 16.2) and Lev/K+ (av. 0.27) ratios over the Arabian Sea with the source-emissions revealed their origin from crop-residue burning. Rather high concentrations of Lev over the Arabian Sea compared to those documented over the Bay of Bengal, East China Sea, Sea of Japan and the western North Pacific further suggests a stronger impact of BB in the continental outflow over this marine basin. Besides, Lev/K+ ratios in marine aerosols exponentially decreased with an apparent increase in ambient relative humidity and temperature over the Arabian Sea during the South Asian outflow, implying a photochemical oxidation of BBOA. Such field-based relationship of Lev with the meteorological parameters can be useful for modelling the impact of BBOA on the surface Ocean. Besides, the aeolian input of sugar-C and water-soluble organic carbon (WSOC) accounted for 83 % and 92 % of that riverine supply to the Arabian Sea, respectively. This means atmospheric dry-deposition of sugars is an important external source of dissolved organic compounds to the surface water.
Display omitted
•High levoglucosan (Lev) levels confirm the biomass burning impact over Arabian Sea.•Molecular distributions/tracer ratios pinpoint crop-residue burning as a major source.•Linear relationship of Lev fraction and stable carbon isotope highlight aging process.•Exponential decay of Lev/K+ with temperature hints photochemical loss during transport.•Aeolain input of sugar-C is comparable to the fluvial input to the Arabian Sea.
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