Analysis of wet deposition characteristics in the city of Guilin, China.

In this study, the rainfall, pH, conductivity, and ionic component data for Guilin from 2015 to 2017 were analyzed. Specifically, the relationship between the pH value of the rainfall, the change of each ion in the rainfall, and the primary ion sources was examined. The main results obtained were as follows. During the 3-year study period, the average annual pH value of Guilin was 5.45 and exhibited a downward trend. The seasonal variation of rainfall acidity was pronounced, with high pH values and low frequencies of acid rain in summer, and low pH values and high frequencies of acid rain in winter. From 2015 to 2017, the relative order of the average concentrations of the ionic components in the rainfall was SO42- > NO3- > Ca2+ > Cl- > NH4+ > Na+ > K+ > Mg2+ > F-, the annual average concentration of each ionic component displayed a downward trend, and seasonal changes were obvious. Only NH4+ showed an upward trend in rainfall. The (SO42-)/(NO3-) ratio was basically < 3 and manifested a downward trend; (Ca2+)/(NH4+) rose sharply in August and September each year. Using correlation analysis and enrichment factor analysis, it was concluded that the rainfall in Guilin is mainly affected by SO2, NOx, and NH3, with the geological conditions in the karst area also contributing a certain amount to the rainfall acidity. Calculating the enrichment factor revealed that most of the Ca2+ came from a crustal source; half the Mg2+ came from the ocean and half came from the crust; and most of K+ and Cl- originated from the ocean. Human activities contributed most of the SO42- and NO3- in the rainfall.