Studies on Temporal Variation of Acid Precipitation in Delhi

Abstract

Precipitation samples were collected as wet-fall only and primarily on event basis in Delhi (capital of India) during the monsoon period of 2005. Concentration of major anions (SO₄^2-, NO₃^– and Cl^–) and cations (Ca²⁺, Mg²⁺, Na⁺ and K⁺) were determined. The pH of the rain water was found to be more than 5.6, showing acidity during the early phase of monsoon, but during the late phase of monsoon pH tendency was towards alkalinity at some locations and acidity at other locations due to lack of proper neutralization of acidic ions. Neutralization is not only due to the local process but also due to the pre-monsoon wind which brings suspended particulate matter (SPM) containing Ca²⁺, Mg²⁺, Na⁺ and K⁺ as well as the local emission of NH₃. In the late mansoon, the concentration of the cations gets reduced because of heavy rainfall and relatively unfavourable condition for their transport from the adjoining areas, where as the anion concentration remains unchanged owing to their continuous emission.