Effect of precipitation on air pollutant concentration in Seoul, Korea

In this study, long-term rainfall data with irregular spatial distribution in Seoul, Korea, were separated into individual precipitation events by the inter-event time definition of 6 hours. Precipitation washout of PM₁₀ and NO₂ concentrations in the air considering various complex factors were analyzed quantitatively. Concentrations of PM₁₀ and NO₂ in the atmosphere were lower under condition of rainfall compared to that of non-precipitation, and a noticeable difference in average PM₁₀ concentrations was observed. The reduction of concentrations of PM₁₀ and NO₂ by rainfall monitored at road-side air monitoring sites was also lower than that of urban air monitoring sites due to continuous pollutant emissions by transportation sources. Meanwhile, a relatively smaller reduction of average PM₁₀ concentration in the atmosphere was observed under conditions of light rainfall below 1 mm, presumably because the impact of pollutant emission was higher than that of precipitation scavenging effect, whereas an obvious reduction of pollutants was shown under conditions of rainfall greater than 1 mm. A log-shaped regression equation was most suitable for the expression of pollutant reduction by precipitation amount. In urban areas, a lower correlation between precipitation and reduction of NO₂ concentration was also observed due to the mobile emission effect.