Water‐soluble organic carbon, dicarboxylic acids, ketoacids, and α‐dicarbonyls in the tropical Indian aerosols

Abstract

Tropical aerosol (PM10) samples (n = 49) collected from southeast coast of India were studied for water‐soluble dicarboxylic acids (C2–C12), ketocarboxylic acids (C2–C9), and α‐dicarbonyls (glyoxal and methylglyoxal), together with analyses of total carbon (TC) and water‐soluble organic carbon (WSOC). Their distributions were characterized by a predominance of oxalic acid followed by terephthalic (t‐Ph), malonic, and succinic acids. Total concentrations of diacids (227–1030 ng m−3), ketoacids (16–105 ng m−3), and dicarbonyls (4–23 ng m−3) are comparative to those from other Asian megacities such as Tokyo and Hong Kong. t‐Ph acid was found as the second most abundant diacid in the Chennai aerosols. This feature has not been reported previously in atmospheric aerosols. t‐Ph acid is most likely derived from the field burning of plastics. Water‐soluble diacids were found to contribute 0.4%–3% of TC and 4%–11% of WSOC. Based on molecular distributions and backward air mass trajectories, we found that diacids and related compounds in coastal South Indian aerosols are influenced by South Asian and Indian Ocean monsoons. Organic aerosols are also suggested to be significantly transported long distances from North India and the Middle East in early winter and from Southeast Asia in late winter, but some originate from photochemical reactions over the Bay of Bengal. In contrast, the Arabian Sea, Indian Ocean, and South Indian continent are suggested as major source regions in summer. We also found daytime maxima of most diacids, except for C9 and t‐Ph acids, which showed nighttime maxima in summer. Emissions from marine and terrestrial plants, combined with land/sea breezes and in situ photochemical oxidation, are suggested especially in summer as an important factor that controls the composition of water‐soluble organic aerosols over the southeast coast of India. Regional emissions from anthropogenic sources are also important in megacity Chennai, but their influence is weakened due to the dispersion caused by dynamic land/sea breeze on the coast.