Chemical characteristics and source apportionment of aerosols over Indian Ocean during INDOEX-1999

Abstract

During INDOEX IFP-99, the samples of aerosols were collected onboard ORV Sagar Kanya over Indian Ocean along the cruise track, for chemical characterization and identification of dominating sources of aerosols. The concentrations of nss-SO 4 , nss-Ca, nss-Mg, NO 3 , K, NH 4 and SO 2 were observed to be significantly higher before ITCZ in northern hemisphere than across ITCZ in southern hemisphere. In this study, variation of concentrations of nss-SO 4 , nss-Ca and nss-K with respect to change in latitude, wind direction, wind speed and relative humidity have been highlighted. North of ITCZ, nss-SO 4 varied from 2.20 to 18.31 μg/m 3 and south of ITCZ from 0.50 to 2.79 μg/m 3 while nss-Ca varied from 0.02 to 0.72 μg/m 3 north of ITCZ and from 0.01 to 0.14 μg/m 3 south of ITCZ. nss-K ranged 0.09-1.43 μg/m 3 and 0.07-0.60 μg/m 3 before ITCZ and across ITCZ respectively. nss-Ca and nss-SO 4 were contributed mainly by NNW and ENE winds while nss-K was observed to be contributed mainly by SSW and ENE winds. Wind speed greater than 4.5 m/s negatively influenced the concentration of nss-Ca concentrations. Correlation coefficients of nss-SO 4 with SO 2 (r = 0.7) and RH (r = 0.5) suggested a significant contribution of nss-SO 4 by aqueous phase oxidation of SO 2 . Using PCA, four major sources namely sea salt, biogenic combustion, secondary SO 4 and crustal contribution were identified over Indian Ocean during INDOEX period.