Chemical characterization of ambient aerosol collected during the southwest monsoon and intermonsoon seasons over the Arabian Sea - Anions and cations

• Published in: Journal of Geophysical Research 1999-11, Vol.104 (D21), p.26
• Main Authors: Johansen, Anne M, Seifert, Ronald L, Hoffmann, Michael R
• Format: Article
• Language: English
• ISSN: 0148-0227

Ambient aerosol samples were collected over the northern Indian Ocean during two one month-long research cruises that took place during the intermonsoon and SW monsoon of 1995. The present paper focuses on the bulk aerosol material, the ions. Intermonsoon samples were strongly influenced by continental material, both of crustal and anthropogenic origin. The crustal component contained 3.2 percent gypsum. While more than half of the total suspended particulate mass (TSP) during the SW monsoon was sea-salt-derived due to the strong winds prevailing during this season, only 1.7 + /- 1.1 percent was found to be of crustal origin. Sulfate (SO4(2-)) sources were determined and quantified with linear regression analyses utilizing specific tracers for the independent variables. Lead (Pb) was found to be a more reliable surrogate for anthropogenic SO4(2-) compared to nitrate (NO3(-)) during the relatively polluted intermonsoon. Soluble calcium (Ca2+) served as the tracer for gypsum, and methane sulfonate served as the tracer for biogenically derived SO4(2-) during both seasons. On the basis of this analysis, 75 percent of the non-sea-salt (NSS) sulfate was found to be of biogenic origin during the SW monsoon with the remaining 25 percent of anthropogenic origin. During the intermonsoon, NSS-SO4(2-) accounted for about 9.2 percent of TSP and had a composition that was 65 percent anthropogenic, 21 percent biogenic, and 14 percent gypsum-derived. (Author)