Precipitation chemistry and stable isotopic characteristics at Wengguo in the northern slopes of the Himalayas

Abstract

The major ions in precipitation can reflect the conditions of the atmosphere, while stable isotopic characteristics provide information on the moisture source. In order to understand the local hydro-chemical features and regional geochemical cycle, it is essential to assess the chemical composition of precipitation and the associated sources. Therefore, a total of 57 precipitation samples (2016 to 2017) for major ions and 178 samples (2013 to 2017) for stable isotopes were collected from the Wengguo station and analyzed to explore the major ionic deposition and stable isotopic characteristics in the northern slopes of the Himalayas. The average pH and electrical conductivity were 6.82?±?0.45 and 15.36?±?11.67 μS cm^?1, respectively. Ca²⁺ followed by K⁺ and Mg²⁺ played a crucial role in neutralizing the precipitation acidity. The major ionic sources in the region were terrigenous (Ca²⁺, HCO₃^?, and Mg²⁺) and sea salt (Na⁺, Cl^?, and Mg²⁺), as well as anthropogenic emissions (SO₄^2? and NO₃^?) and biomass burning (K⁺). The total deposition flux of the major ions was higher in 2016 than in 2017 and was influenced by the higher precipitation. The average values of δ¹⁸O and δD in precipitation were???15.22?±?5.17 ‰ and???116.01?±?41.31 ‰, respectively. The precipitation stable isotopes were not significantly correlated to the local air temperature but the precipitation amount. Moreover, the variation in stable isotopes, local meteoric water line, and d-excess indicated the existence of continental and monsoon moisture transport systems. The transport of chemicals over the high elevation region from polluted cities in South Asia via moisture originating in the Bay of Bengal and the Arabian Sea was determined based on the source identification, clusters of air mass backward trajectory analysis, and the National Center for Environmental Prediction Final dataset. Thus, the ionic concentrations and stable isotopic characteristics of the precipitation from this study provided a valuable dataset to assess the atmospheric environment in the northern slopes of the Himalayas at Southern Tibetan Plateau.