Heavy rain falls within an hour of all the dates surveyed. All the rest of the precipitation is light rain, with low PM reduction efficiency. There were no cases where rainfall intensity was more than 10 mm, and there were many cases where accumulated rainfall was more than 4 mm if the duration was more than 3 hours. Therefore, despite the possibility of reducing PM through precipitation, the cause of the increase in PM the next day can be largely summarized into two types, domestic and foreign. If particular matter or yellow dust enters from abroad, it will reach the central part of Korea within a day to increase the concentration of PM, considering the wind speed of the month. And when atmospheric congestion occurs in Korea, PM levels tend to increase in a short period of time.