Aerosol size characteristics over the Arabian Sea and Indian Ocean: extensive sub-micron aerosol loading in the Northern Hemisphere

Abstract

Aerosol optical depth (AOD) measurements in the spectral range 0.3–1.6 mm have been carried out using a multi-channel solar radiometer onboard ORV Sagar Kanya to understand the interaction between continental and marine aerosols. Experiments have been carried out under clear sky conditions for 22 days during 20 January–12 March 1999 covering the latitude belt between 17°N and 20°S, and longitude belt between 71°E and 59°E, over Indian Ocean and Arabian Sea as part of INDOEX IFP-99. Results show larger particle abundance, close to the Indian coast during forward leg compared to that of return leg of the cruise. AODs, in general, exhibit larger values north of ITCZ compared to that of south of ITCZ. The spatial distribution of AOD at 0.502 mm shows greater values north of ITCZ with significant latitudinal gradient compared to that of south of ITCZ. Aerosol size spectrum, derived from spectral AODs, shows monomodal distribution for both pristine oceanic environment (south of ITCZ) and for polluted environment (north of ITCZ).