Abstract
Abstract. Marine aerosol samples collected from the South China Sea (SCS) to the eastern Indian Ocean (EIO) during a cruise from 10 March to 26 April 2015 were studied for diacids and related compounds. In view of air mass backward trajectories, source regions, and geographical features, the cruise area was categorized into the South China Sea (SCS), the eastern Indian Ocean off the coast of western Indonesia (EIO-WI), the EIO off the coast of Sri Lanka (EIO-SL), Malacca, and the Sri Lanka docking point (SLDP). Total concentrations of diacids, oxoacids, and α-dicarbonyls were high at the SLDP, followed by the SCS and Malacca, and they were the low in the EIO-WI. In this study, oxalic acid (C2) was the dominant diacid during the cruise, followed by malonic acid (C3) in the SCS, EIO-WI, EIO-SL, and Malacca, and succinic acid (C4) was relatively more abundant than C3 diacid at the SLDP. Except for SLDP, C3∕C4 mass ratios were always greater than 1, and no significant difference was observed during the cruise. The C2∕C4 and C2∕total diacid ratios also showed similar trends. The average mass ratios of adipic acid (C6) to azelaic acid (C9) were less than unity except for in the EIO-WI; the mass ratios of phthalic acid (Ph) to azelaic acid (C9) were less than 2 except for in the SCS. The concentrations of diacids were higher when the air masses originated from terrestrial regions than when they originated from remote oceanic regions. Based on the molecular distributions of organic acids, the mass ratios, and the linear correlations of selected compounds in each area, we found that the oxidation of biogenic volatile organic compounds (BVOCs) released from the ocean surface and subsequent in situ photochemical oxidation was the main contributor to diacids, oxocarboxylic acids, and α-dicarbonyls from the SCS to the EIO. In addition, the continental outflow, which is enriched in anthropogenic VOCs and their aged products, influenced the organic aerosol loading, particularly over the SCS. Emissions from Sri Lanka terrestrial vegetation as well as fossil fuel combustion and subsequent photochemical oxidation also played a prominent role in controlling the organic aerosol loading and the molecular distribution of diacids and related compounds at the SLDP.
Highlights
Land–sea–air interaction is one of the most important issues in Earth system science
The mean mass concentrations of organic carbon (OC) and elemental carbon (EC) in the South China Sea (SCS) were 1.5 times (OC mean of 0.82 μg m−3) and 1.7 times (EC mean of 0.16 μg m−3) higher than those reported by Fu et al (2013a) in the SCS in late February 1990
The results showed that organic aerosols produced by biogenic volatile organic compounds (BVOCs) emitted from the ocean surface were more aged in the EIOWI and eastern Indian Ocean (EIO)-SL than in the SCS and at Malacca, where they were affected by anthropogenic emissions
Summary
Land–sea–air interaction is one of the most important issues in Earth system science. Atmospheric aerosols are one of the major components in the Earth’s atmosphere and are the key carriers of the global biogeochemical cycle of nutrients (Zhuang et al, 1992; Li et al, 2017; Tan et al, 2011). The abundant diacids, oxoacids, and α-dicarbonyls are reported to be the major fraction of water-soluble organic aerosols (Sorooshian et al, 2010; Ervens et al, 2011; Cong et al, 2015); these water-soluble aerosols enhance the capacity of aerosol particles to act as cloud condensation nuclei and ice nuclei in the atmosphere 2016; Vergara-Temprado et al, 2017; Huang et al, 2018), whereas water-insoluble substances such as lipid-class compounds can reduce their hygroscopic activity (Kawamura et al, 2017)
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