Rainwater chemistry in the North Western Himalayan Region, India

Abstract

Precipitation chemistry studies were conducted at Kothi (32.31°N, 77.20°E), a rural Indian location, in the North Western Himalayas during June to October of 2006 and 2007. The volume weighted mean pH values ranged from 5.16 to 6.36 with a mean of 5.68±0.26 indicating mostly alkaline precipitation events. However, 18% samples were found acidic due to dominance of acidic components. The alkaline to acidic ions ratio (1.05) confirms that acidic components are neutralized by alkali radicals in rainwater. Of the total ionic composition 159μeq/l, in rainwater samples, dominant were Ca2+ (19%) followed by Na+ (14%). Among the anions, Cl− (17%) was slightly higher than SO42− (16%) and NO3− (11%). The ratio (NO3−+Cl−)/SO42−) 1.05 indicates acidity in rainwater by the cumulative effects of HNO3, H2SO4 and HCl. The ratios NH4+/NO3− as 0.76 and NH4+/SO42− as 0.50 show the pre-dominance of atmospheric NH4NO3 and (NH4)2SO4. Significant correlation between Na+ and Cl− (r=0.97; p<0.0001) and between SO42− and NO3− (r=0.60; p<0.0001) indicates their origin from similar sources. Neutralization factor calculations show that Ca2+ plays a major role in the neutralizing processes. Enrichment factors indicate that Ca2+, SO42− K+ and Mg2+ were originated from non-marine sources. The principle component analysis indicates the influence of transportation of air-born primary and secondary particles on the chemical composition of rainwater.