Neutralization of rainwater acidity at Kanpur, India

Abstract

Particulate matter (PM) levels show significant seasonal variability and this can influence the neutralization of rainwater acidity. Months were grouped in two periods: monsoon (July to October) and non-monsoon (November to June) for studying the seasonal variability in PM and rainwater composition. To clearly establish the cause effect relationship of acid rain neutralization, a two tier model was proposed involving source apportionment of particulates at two levels: (i) ambient air and (ii) rainwater particulate interaction. For modelling purpose, PM₁₀ (n = 100), soil (n = 4) and rainwater (n = 83) samples were collected at Kanpur, India during 2000–2002. The collected samples were analysed for metals and water soluble ion composition to employ factor analysis for source identification. Knowledge of statistical correlation and chemistry fundamentals were combined to estimate the sources for acid rain neutralization. NH₄ + was a dominating ion responsible for neutralizing the acidity of rainwater in monsoon period and Ca²⁺ was dominating in non-monsoon period. Components of secondary particles (SO₄²⁻ and NO₃⁻) showed affinity with NH₄⁺, signifying the major role that ammonia can play if present in excess of stoichiometric requirements.