Ambient aerosol samples were collected over the Arabian Sea during the month of March 1997, aboard the German R/V Sonne, as part of the German JGOFS project (Joint Global Ocean Flux Study). This is the third study in a series of analogous measurements taken over the Arabian Sea during different seasons of the monsoon. Dichotomous high volume collector samples were analyzed for anions and cations upon return to the laboratory. Anthropogenic pollutant concentrations were larger during the first part of the cruise, when air masses originated over the Indian subcontinent. Total NSS-SO42- concentrations amounted to 2.94 ¿ 1.06 ¿g m-3 of which 92.1 ¿ 4.5% was present in the fine fraction. NSS-SO42- source apportionment analysis with multivariate linear regression models revealed that in the coarse fraction half is biogenically and half anthropogenically derived, while in the fine fraction only 6% seemed of biogenic origin and 84% anthropogenic and 10% crustal in nature. Chloride deficits up to 99.1% in the fine fraction were observed. The average Cl- deficit in the fine fraction was 89.0 ¿ 9.4%, potentially related to NSS-SO42- acid displacement and Cl reactive species formation, while in the coarse fraction it was 25.6 ¿ 21.3%, with NO3- being the preferred species for acid displacement.