Chemical Composition of Water Soluble Inorganic Species in Precipitation at Shihwa Basin, Korea

Abstract

Weekly rain samples were collected in coastal areas of the Shihwa Basin (Korea) from June 2000 to November 2007. The study region includes industrial, rural, and agricultural areas. Wet precipitation was analyzed for conductivity, pH, Cl-, NO3-, SO42-, Na+, K+, Mg2+, NH4+, and Ca2+. The major components of precipitation in the Shihwa Basin were NH4+, volume-weighted mean (VWM) of 44.6 mu eq.L-1, representing 43% of all cations, and SO42-, with the highest concentration among the anions (55%) at all stations. The pH ranged from 3.4 to 7.7 with a VMM of 4.84. H+ was weakly but positively correlated with SO42- (r = 0.39, p < 0.001) and NO3- (r = 0.38, p < 0.001). About 66% of the acidity was neutralized by NH4+ and Ca2+. The Cl-/Na+ ratio of the precipitation was 37% higher than seawater Cl-/Na+. The high SO42-/NO3- ratio of 2.3 is attributed to the influence of the surrounding industrial sources. Results from positive matrix factorization showed that the precipitation chemistry in Shihwa Basin was influenced by secondary nitrate and sulfate (41% +/- 1.1%), followed by sea salt and Asian dust, contributing 23% +/- 3.9% and 17% +/- 0.2%, respectively. In this study, the annual trends of SO42- and NO3- (p < 0.05) increased, different from the trends in some locations, due to the influence of the expanding power generating facilities located in the upwind area. The increasing trends of SO42- and NO3- in the study region have important implications for reducing air pollution in accordance with national energy policy.