Chemical characteristics of precipitation and the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain,northwestern China

Precipitation chemistry analysis is essential to evaluate the atmospheric environmental quality and identify the sources of atmospheric pollutants. In this study, we collected a total of 480 precipitation samples at 6 sampling sites in the northern and southern slopes of Wushaoling Mountain from May 2013 to July 2014 to analyze the chemical characteristics of precipitation and to identify the main sources of ions in precipitation. Furthermore, we also explored the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain based on the precipitation chemistry analysis. During the sampling period (from May 2013 to July 2014), the pH values, EC (electrical conductivity) values and concentrations of cations (Ca²⁺, Mg²⁺, Na⁺, K⁺ and NH₄⁺) and anions (SO₄^2-, NO₃^-, Cl^-, NO₂^- and F^-) in precipitation were different in the northern and southern slopes at daily and seasonal time scales, with most of the values being higher in the northern slope than in the southern slope. The chemical type of precipitation in the southern and northern slopes was the same, i.e., SO₄^2--Ca²⁺-NO₃^--Na⁺. The concentrations of ions in precipitation were mainly controlled by terrigenous material and anthropogenic activities (with an exception of Cl^-). The concentration of Cl^- in precipitation was mainly controlled by the sea salt fraction. The concentrations of Na⁺ and Cl^- showed an increasing trend after the occurrence of sand dust events both in the northern and southern slopes. In addition, after the occurrence of sand dust events, the concentrations of K⁺, Mg²⁺, SO₄^2-, NO₃^- and Ca²⁺ showed an increasing trend in the southern slope and a decreasing trend in the northern slope. It is our hope that the results may be helpful to further understand the atmospheric pollution caused by sand dust events in the Wushaoling Mountain and can also provide a scientific basis for the effective prevention of atmospheric pollution.