Chemical Composition Characteristics and Source Contributions of Precipitation in Typical Cities on the North Slope of Tianshan Mountain in Xinjiang during 2010–2019

Abstract

This work presents the results of a ten-year investigation (2010–2019) on the characteristics and sources of precipitation pollution in typical cities locating in the economic belt on the North Slope of Tianshan Mountain, Xinjiang. The water-soluble ions’ characteristics (Na+, NH4+, K+, Mg2+, Ca2+, F−, Cl−, SO42−, NO3−), neutralizing capacity, wet deposition and sources of precipitation in Urumqi, Karamay and Yining during 2010–2019 were compared and analyzed. The study showed that from 2010 to 2019, the pH value of precipitation in Urumqi, Karamay and Yining varied from 4.18 to 10.55 with a volume-weighted mean (VWM) pH of 6.33, and the pH value showed an upward trend overall. The VWM electrical conductivity (EC) of the precipitation was the highest in Urumqi and the lowest in Yining, indicating that Urumqi was the most polluted and Yining was relatively clean. The most important cation in the precipitation of the three cities was Ca2+, and the most important anion was SO42−. The ratio of SO42−/NO3− indicated that the air pollution in Urumqi and Yining belonged to the typical coal-smoke air pollution, while there was compound pollution in Karamay. As can be seen from the neutralization factor, Ca2+ had the strongest neutralization ability, followed by Na+ and NH4+. Nitrate and sulfate in the atmosphere of Urumqi, Karamay and Yining are likely to exist in the form of NH4NO3, CaSO4 and (NH4)2SO4•CaSO4•2H2O. Wet deposition flux analysis of S and N showed that S pollution of the precipitation in Urumqi showed a decreasing trend, while N pollution showed an increasing trend. S pollution of the precipitation in Karamay gradually decreased, while N pollution of the precipitation in Yining became more and more serious. By analyzing origins of major ions in precipitation, it is concluded that human activities (industry, agriculture, heating, and transportation) are the main sources of ions in precipitation, and natural sources (soil dust) also play an important role.