Rainwater composition at a regional representative site of a semi-arid region of India

Rainwater samples (N = 51) were collected at Rampur, an area free from anthropogenic activity during the monsoon of 1997 and 1998. The concentration of ions follows a general pattern as Ca > NH4 > Mg > SO4 > Cl > F > Na > NO3 > K > HCOO > CH3 COO. The pH of precipitation ranges between 5.9 and 7.4. The levels of Ca and Mg at this site are higher than other remote sites, probably dominated by particles of soil origin. Good correlation between Ca, NO3, SO4, HCOO and CH3COO indicate that a fraction of NO3, SO4, HCOO and CH3COO may be derived from soil or associated with Ca and Mg after neutralization. The order of neutralization factor Ca (2.19) > NH4 (1.26) = Mg (1.26) indicates that major neutralization occurred by Ca. Factor analysis suggested that Ca, Mg, Na, K, NO3, SO4, HCOO and CH3COO are contributed by soil. NH3 is known to exist as (NH4)(2)SO4, NH4NO3 and NH4Cl. They may be formed in the atmospheric water droplets by scavenging of aerosols and reaction of gaseous species.