A Long Term Study on Chemical Composition of Rainwater at Dayalbagh, a Suburban Site of Semiarid Region

Rainwater samples were collected for the monsoon period of 1988 and 1991–1996 at Dayalbagh (Agra), a suburban site situated in semiarid region. The mean pH was 7.01 ±1.03 well above 5.6, which is the reference pH. Concentration of Ca2+ was observed to be highest followed by Mg2+, NH4 , SO 2− 4 , Cl −, NO3 , Na+, F− and K+. The ratios of SO 2− 4 + NO3 and Ca2+ + Mg2+ (TA/TC) have been considered as indicator for acidity. In the Agra region ratio of TA/TC is quite below 1.0 indicating alkaline nature of rainwater. The lowest value of 0.24 was observed in 1991 likely due to the lowest rain depth of the decade. The highest value of 0.54 was observed in 1996, a year with a large rain depth and increase in line (vehicular traffic) and area sources (population growth). Good correlation between Ca2+ and NO3 , Ca2+ and SO 2− 4 and SO 2− 4 and NO − 3 , indicates that wind carried dust and soil play a significant role in neutralization of precipitation acidity.