[Reason for choosing Seoul as the analysis region]

In this study, we used the data on precipitation and fine dust (PM10) at the Korea Meteorological Agency Meteorological Data Opening Portal. The study area was set at the Seoul Observatory of the Korea Meteorological Agency (37.57 north latitude, 126.98 east longitude) in Songwol-dong, Jongro-gu, Seoul. The PM10 observation network of the Ministry of the Environment has more specific data on the fine dust observation data, but it has been unified to the data of the Seoul Observatory of the Korea Meteorological Agency for accurate comparison with precipitation. Mircea (2000) assumed that the collision efficiency of the urban aerosol particles with the raindrops is higher than others. So we choose Seoul metropolitan as the analysis region to easily examine our hypothesis.

[Reason for setting February to May as the analysis period]

[2019 Average Monthly PM10 Concentration - Seoul]

: The monthly average concentration of PM 10 in March was the highest at 69 μg/m³, followed by 66 μg/m³ in January, 57 μg/m³ in February, and 52 μg/m³ in May. December (42 μg/m³), April (41 μg/m³) and November (40 μg/m³) were also high, similar figures.

[2020 Average Monthly PM10 Concentration - Seoul]

: The monthly average concentration of PM10 in March was the highest at 45 μg/m³, followed by 44 μg/m³ in April. January (42 μg/m³), February (41 μg/m³), November (42 μg/m³), and December (42 μg/m³) were also high, similar figures.

* Months of high PM 10 concentration among 2019 & 2020: January, February, March, April, May, November, December

- Since our group limited "precipitation" to "rain," January and December, which are more likely to cause snow than rain, were excluded from the analysis.

- November was excluded to establish and analyze a continuous period.

> We decided to investigate the correlation between "rain" and "PM 10" from February to May data.

[Characteristics of climate and particular matters in research area, Seoul]

The average annual temperature in Seoul is12.5℃. The average temperature per month is -2.4°C in January, the average temperature per month is 25.7°C in August, and the annual temperature range is 28.1°C.
The sum of summer precipitation (June, July, and August) was 892mm, accounting for about 61% of annual precipitation, which is very high in summer precipitation. On the other hand, the total amount of precipitation in winter (December, January, and February) was 67.3 mm, accounting for only 5% of the annual rainfall.
The average wind speed per month is 2.3 m/s, the lowest monthly wind speed of 1.9 m/s in September and the highest of 2.8 m/s in March and April.
The average annual relative humidity in Seoul is 64%, and the monthly relative humidity is the lowest at 56%, in April, and the highest at 78%, in July. The average relative humidity in summer is 74%, which is very humid, and the relative humidity in spring and winter is about 60%, which is relatively dry.
Seoul is geographically surrounded by Bukhansan, Dobongsan, and Gwanaksan, and there are many factors that can affect air quality deterioration due to population and traffic concentration in the Seoul metropolitan area, industrialization of China, desertification of the continent, and influence of western wind.