Anthropogenic sulphate aerosols and large Cl-deficit in marine atmospheric boundary layer of tropical Bay of Bengal

• Published in: Journal of atmospheric chemistry 2010-06, Vol.66 (1-2), p.1-10
• Main Authors: Sarin, Manmohan, Kumar, Ashwini, Srinivas, Bikkina, Sudheer, A. K., Rastogi, Neeraj
• Format: Article
• Language: English
• Subjects: Aerosols; Anthropogenic factors; Applied sciences; Atmospheric aerosols; Atmospheric boundary layer; Atmospheric chemistry; Atmospheric pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Boundary layers; Chlorine; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Human influences; Marine; Marine environment; Marine pollution; Meteorology; Ocean-atmosphere interaction; Oxidizing agents; Particles and aerosols; Planetary boundary layer; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; Salt; Salts; Sulfides; Sulfur dioxide; Toy industry
• ISSN: 0167-7764; 1573-0662
• DOI: 10.1007/s10874-011-9188-z

Our long-term study provides an unequivocal evidence for near-quantitative (80–100%) depletion of chloride from sea-salts in the marine atmospheric boundary layer (MABL) of tropical Bay of Bengal. During the late NE-monsoon (Jan-Mar), continental outflow from south and south-east Asia dominate the wide-spread dispersal of pollutants over the Bay of Bengal. Among anthropogenic constituents, SO 4 2− (range: 0.6–35 μg m −3 ) is the most dominant. The non-sea-salt SO 4 2− (nss-SO 4 2− ) constitutes a major fraction (55–65%) of the aerosol water-soluble ionic composition (WSIC), whereas contribution of NO 3 − is relatively minor. The magnitude of Cl-deficit (with respect to its sea-salt proportion) exhibits linear increase with the excess-nss-SO 4 2− (excess over NH 4 + ). We propose that displacement of HCl from sea-salt aerosols by H 2 SO 4 is a dominant reaction mechanism for the chloride-depletion. These results also suggest that sea-salts could serve as a potential sink for anthropogenic SO 2 in the downwind polluted marine environment. Furthermore, loss of hydrogen chloride, representing a large source of reactive chlorine, has implications to the oxidant chemistry in the MABL (oxidation of hydrocarbons and dimethyl sulphide).