Influence of air mass trajectories on the chemical composition of precipitation in India

Chemical composition of precipitation was measured with wet-only samplers a t a rural site at Bhubaneswar in eastern India during 1997-1998. All rain e vents were compared with trajectories and precipitation fields from the ECM WF. The pH and ionic concentrations were found to vary systematically,vith the origin of air and the amount of rainfall along the trajectory. A season al cycle for pH was found with a monthly median pH below 5.0 during October December. The highest monthly median concentration of Ca2+ was found in Ma y with 20 mu mol l(-1) and for SO42- in January with 52 mu mol l(-1). Sampl es with trajectories within 400 km from Bhubaneswar during the last 5 days were found to have a median pH slightly below 5.0 as an average. These samp les also had the highest concentration for all measured ions, indicating la rge pollution sources within the region. Samples with continental origin sh owed a decrease of similar to 70% in concentration if there had been rain d uring > 50% of the last 5 days compared to rain during < 50% of the last 5 days. High concentrations of Na+ and Cl- were also found in continental sam ples. Resuspension of previously deposited sea salt is believed to be the r eason. The data were compared with data from three other sites in western I ndia and higher concentrations of almost all ions (NH4+ being the exception ) compared to Bhubaneswar were found at the west coast in monsoon samples. (C) 2001 Elsevier Science Ltd. All rights reserved.