Influence of crustal aerosols on wet deposition at a rural site of North-East India

A total of 42 rain water samples were collected for a period of one year, March 2005 to February 2006, at Jorhat, a rural site of North-East India. The pH of the samples varied from 4.1 to 7.1 with a mean 5.5 showing the acidic nature of rainwater with reference to 5.6 (natural pH of rain water due to CO2 equilibrium in the atmosphere). More than 50% of the rain events have been found to be acidic. Mean concentrations of major ions in the rain water followed the order SO > Ca2+ > NH > NO > PO > H+ > HCO > Na+ > Mg2+ > Cl– > K+ > F–. Ca2+, NH and Mg2+ have shown a neutralization factor less than 1, indicating partial neutralization of anions. EFSoil indicated that soil plays a major role in rain water composition. Maximum concentration for most of the ionic species has been observed during winter followed by summer, post-monsoon and monsoon periods, respectively. Occurrence of acid rain events has been observed throughout the year suggesting that the soil is acidic.