Chemical composition of rainwater in the Yulong Snow Mountain region, Southwestern China

Abstract

We evaluated the chemical composition of rainwater samples in the Mt. Yulong region, southeastern Tibetan Plateau. A total of 176 rainwater samples were collected from Lijiang City and Ganhaizi Basin in the study area. All samples were analyzed for total dissolved solids (TDS), conductivity, pH, major cations (Na+, K+, NH4+, Ca2+, Mg2+) and anions (F−, SO42−, Cl−, NO3−). The daily rainwater pH values ranged from 4.55 to 7.43, with an average value of 5.95 for the region. High values of pH were attributed to the neutralization by natural alkaline of local dust particles with rich CaCO3. The average total dissolved solid was 5.27mg/L, and the EC ranged between 2.14 and 57.2μscm−1 with an average value of 11.5μscm−1. These parameters indicated low chemical concentrations in the rainwater. The major ions showed relatively high Ca2+, SO42−, and NH4+ concentrations, accounting for 40%, 25%, and 16% of the total ion mass, respectively. Linear regression analysis confirmed that the rainwater pH was mainly controlled by the species of SO42−, NO3−, NH4+ and Ca2+. Factor component analysis applied to the studied variables indicated that the extracted three components accounted for 90% of the total variance for Ganhaizi Basin, and the extracted two components accounted for 73% of the total variance for Lijiang City. The study identified association of the three ion groups: Ca2+, Mg2+, K+ and F−, related to the origins of crustal sources; NH4+, SO42− and NO3− associated with local anthropogenic activities (agriculture, biomass burning, vehicle emissions), and Cl− and part of Na+ related to the contribution of sea salts from long-range atmospheric transport.