Variation Trend and Analysis of Water-soluble Ions in Precipitation from 2017 to 2021 in Kunming

The pH value of precipitation and monitoring data of nine water-soluble ions(SO₄^2-、NO₃^-、Cl^-、F^-、K⁺、Na⁺、Ca²⁺、Mg²⁺、NH₄⁺) from five monitoring stations in the major metropolitan area were analyzed from 2017 to 2021 to better understand the trend of water-soluble ions in Kunming precipitation. According to the data, the pH of precipitation in Kunming was alkaline during the time period, with no acid rain observed. SO₄^2-, NH₄⁺, and F-concentrations decreased year after year. The concentrations of Cl^-、NO₃^-、K⁺、Na⁺、Ca⁺、Mg²⁺ all showed an increasing trend. The NO₃^-/SO₄^2-（N/S） ratio increased from 0.33 to 0.58, indicating that acidic pollutants in precipitation in Kunming changed from sulfuric acid type to sulfuric acid/nitric acid type. The districts of Panlong, Guandu, and Wuhua have the most comparable precipitation characteristics.