Spatio-temporal variation of pH and ionic concentrations in precipitation: interaction between two contrasting stationary sources affecting air quality

Meteorological and geological factors affecting the pH and ionic concentrations of precipitation were investigated from Jecheon City, Korea. The air quality of the study area is affected by two contrasting stationary sources: 1) a coal-fired power plant to the east-northeast and 2) limestone quarries and cement-manufacturing factories to the east to south-southeast of Jecheon. The temporal change of rainwater chemistry is affected by the interaction between acidic gases and alkaline substances from the above two sources. Accordingly, rainwater pH at a city center widely varies from 4.9 to 8.3. Acidic gases from the power plant are likely to acidify the rainwater pH. As the prevailing wind direction during rainfall events shifted to ENE-SSE, rainwater pH at the city center rapidly increased to >6.5 (up to 7.8). Concomitantly, ionic concentrations (esp., Ca, K, and Na) increased sharply, especially when winds are brown from SE, probably due to major influences of particles coming from limestone quarries. The enrichment factor analyses of acidity and cations also indicate that the acidic components in precipitation are mostly neutralized by limestone particles. In addition, rainwater chemistry showed a spatial variation as a function of the direction and distance from the above two sources. Our results demonstrate a good example of competing roles between the anthropogenic acidic source and the geologic alkaline source.