Occurrence of acid rain over Delhi

Precipitation samples were collected as wet-fall only and primarily on even t basis in Delhi during the monsoon period of 1995. Concentrations of major anions (SO42-, NO3- and Cl-) and cations (Ca2+, Mg2+, Na+ and K+) were det ermined. The pH of the rain water was found to be more than 5.6, showing al kalinity during the early phase of monsoon, but during the late phase of mo nsoon pH tendency was towards acidity due to lack of proper neutralization of acidic ions. Neutralization is not only due to the local process but als o due to the pre-monsoon `Andhi' which brings Suspended Particulate Matter (SPM) containing Ca2+, Mg2+, Na+ and K+ as well as the local emission of NH 3. In the late monsoon the concentration of cations gets reduced because of heavy rainfall and relatively unfavourable condition for their transport f rom the adjoining areas, whereas the anion concentrations remain unchanged owing to their continuous emission.