Chemical Characteristics of Spring Rainwater at an Urban Site of Southeast Korea

This study investigated the chemical characteristics of rainwater at Daeyeon dong, Busan, South Korea, from February 2020 to May 2020. In the total 6 rain events, rainwater samples were continuously collected every 50 mL from the beginning of the precipitation using rainwater collecting devices. The collected rainwater water samples were analyzed for water-soluble anions (SO₄^2-, NO₃^-, Cl^-) and cations (NH₄⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺), pH, electrical conductivity (EC). As a result, pH showed a strong negative correlation with EC (r = -0.95). An average pH value during every rain event increased from 4.1 to 4.6, while an average value of EC decreased from 117.6 to 29.7 μS/cm. Dominant anions in the rainwater were NO₃^- > Cl^- > SO₄^2-. Sulfate showed a positive correlation (r = 0.79) with nitrate, which can be attributed to human activities such as burning fossil fuels. Dominant cations in the rainwater were Ca²⁺, Na⁺, and NH₄⁺. A strong positive correlation (r = 0.99) between Mg²⁺ and K⁺ can be considered to be derived from the soil. Similarly, a strong positive correlation (r = 0.99) was observed between the sea-salt species Na⁺ and Cl^-, indicating a common marine source. The concentrations of all ions in the rainwater samples decreased with precipitation duration. In particular, the concentration of the NO₃^-, the main ionic component of the rainwater, decreased by approximately 83% from 9.09 to 1.53 mg/L. The concentration of the Ca⁺ showed a similar temporal pattern with NO₃^- and decreased by approximately 87%.