High-Altitude Air Pollutants Monitored from Rainwater Chemistry in the Central Himalaya

Based on the ion chromatography method, the chemical characterization of rainwater (RW) samples collected over Srinagar (a location in central Himalaya) has been done during monsoon 2016 (MON-2016). The rainwater shows near acidic pH values ranging from 5.1 to 6.2 (average, 5.7 ± 0.6) during the study. The average ionic concentrations of 97 ± 10 μeq/1 were reported during MON-2016. Ca²⁺ has significantly high contribution of 24% as compared to NH₄⁺ (18%), Na⁺ (9%), K⁺ (4%), and Mg²⁺ (3%) among cations, whereas Cl⁻, SO₄²⁻, and NO₃⁻ have contribution of ~ 15, 11, and 7%, respectively, among anions during chemical analysis. We have reported SO₄²⁻/NO₃⁻ ratio as 1.49, which shows contribution of 60 and 40% from SO₄²⁻ and NO₃⁻ ions within the predicted limit of RW (H₂SO₄, 60–70%, and HNO₃, 30–40%). Ca²⁺, Mg²⁺, and NH₄⁺ have neutralization factors as 2.51, 0.37, and 2.01, respectively, due to the neutralization of acidic species in RW. The non-sea salt (NSS) contribution to total Ca²⁺, K⁺, and Mg²⁺ indicates the major contribution from crustal origin, whereas the NSS contribution to the total Cl⁻ and SO₄²⁻ was from the anthropogenic source. The principle component analysis (PCA) indicates that the first factor (i.e., natural sources, mainly dust and sea salts) has only ~ 9% variance. In contrast, the second factor (i.e., fossil fuel and biomass burning) has ~ 17% variance, and the third factor has 27% variance may be due to soil, agricultural, and biomass burning origin. The rest of the contributions are from mixed emission sources as well as by the transport of polluted air mass from the Indo-Gangetic Plain (IGP) and Punjab Rajasthan, Pakistan, and Afghanistan. This manuscript helps to understand the impact of crustal and anthropogenic sources in rainwater over the central Himalaya region of Uttarakhand.