Transport of Ca2+ and SO42- aerosols during southwest monsoon from north African and Gulf countries towards India

Abstract

Precipitation samples were collected over Arabian Sea during Arabian Sea Monsoon Experiment (ARMEX) campaign for the period June- August 2002 onboard Ocean Research vessel Sagar Kanya. All the rain water samples were analysed for pH and major water soluble ionic components. The pH of rain water was alkaline and the order of chemical composition is followed as Cl^- > Na⁺ > Ca²⁺ > SO₄^2- > Mg²⁺ > K⁺ > NO₃^- > NH₄⁺. Sea salt components were dominant (~ 90%) in precipitation. Significant amounts of non sea salt Ca²⁺, SO₄^2- and trace amounts of NO₃^-, NH₄⁺ were found in precipitation samples whereas, no non sea salt fraction was observed in case of K⁺ and Mg²⁺, indicating that they were totally originated from sea. Rain water data was interpreted in terms of long range transport and back ground pollution to find out the sources of non sea salt components. Back-trajectories showed the presence of air masses originated over North African and Gulf continents towards observational point and they may possibly be carrying non sea salt Ca²⁺ and SO₄^2- aerosols.