Chemical composition of cloud and rainwater at a high-altitude mountain site in western India: source apportionment and potential factors.

Abstract

This study focuses on the chemical composition of cloud water (CW) and rainwater (RW) collected at Sinhagad, a high-altitude station (1450m AMSL) located in the western region of India. The samples were collected during the monsoon over two years (2016-2017). The chemical analysis suggests that the concentration of total ionic constituents was three times higher in CW than in RW, except for NH4+ (1.0) and HCO3- (0.6). Compared to RW, high concentrations of SO42- and NO3- were observed in CW. The weighted average RW pH (6.5 ± 0.3) was slightly more alkaline than CW pH (6.1 ± 0.5). This can be attributed to the high concentrations of neutralizing ions such as nss-Ca2+, nss-Mg2+, K+, and NH4+, indicating the greater extent of wet scavenging during rainfall. These ions counteract the acidity generated by SO42- and NO3-. A high correlation between Ca2+, Na+, K+, NO3-, and SO42- makes it difficult to estimate the contribution of SO42- from different sources. Anthropogenic sulfur emissions and soil dust significantly influence the ionic composition of clouds and rain. Positive matrix factorization (PMF) was used to identify the contribution of different sources to the samples. In the CW, the extracted factors were cooking and vehicles, aging sea salt, agriculture, and dust. In RW, the factors were industries, cooking and vehicles, agriculture and dust, and aging sea salt. The findings of this study have significant implications for the monsoon build-up, ecosystems, agriculture, and climate change.