Acidification and neutralization potentials of rainwater at University of Peradeniya

Abstract

Constituents present in rainwater affects compositional changes leading to acidification or neutralization, and hence the quantification of constituents in rain water. In this respect, the purpose of the present study was to establish a relationship between acidification and neutralization potential of rainwater particulates via bulk precipitation and ambient air quality via dry deposition. Analysis of 30 samples of bulk deposition and 11 samples of dry deposition collected during the four month period from May to September, 2013 at the University of Peradeniya premises for main ions responsible for acidification and neutralization reveals that Na+, Mg2+, Ca2+, K+, NH4 +, NO3  and SO4 2- were major ions present in the samples, and further, Ca2+ and NH4 + dominated constituents for neutralization of rainwater acidity, while NO3  and SO4 2- led to high level of acidity. The regression analysis between the summation of the concentrations of NO3  and SO4 2− vs. the summation of the concentrations of Ca2+ and NH4 + reveals that there is a significant correlation with r = 0.66 for bulk precipitation although the correlation is not good for dry deposition with r = 0.38. This difference can be attributed to the different deposition rates of particulates present in ambient air. . Regression analysis applied on each variable demonstrates that, Ca2+ can be present as CaSO4 and Ca(NO3)2 and NH4 + can be present as (NH4)2SO4 and NH4NO3. Further analysis of the results of compositional variables indicates that 53.3% of SO4 2 can be explained by Ca2+ and NH4 +in bulk precipitation, among which 47.5% appears as CaSO4 and only 5.8% as (NH4)2SO4. Further, only 19% of the NO3  is explained by both Ca2+ and NH4 + out of which 6% appears as Ca(NO3)2 and 13% as NH4NO3. In dry deposition, 33.5% of SO4 2 and 95.4% NO3  were explained by the above two cationic independent parameters, and 33% of SO4 2 appears as CaSO4 and only about 0.5% as (NH4)2SO4. Among 95.4% of explained NO3 , 39.2% appears as Ca(NO3)2 and 56.2% NH4NO3. The linear regression analysis suggests that, Ca2+ is involved in a higher percentage (62.5%) for the neutralization process, whereas the involvement of NH4 + is at lower level of 37.5%.