Paper 1 : Estimation of Effective Rainfalls Affecting the Reduction of Atmospheric Fine Dust

[Fig 1. Changes in precipitation and PM10 over 48 hours on 2014.07.24. ~ 2014.07.25]

00:00 ~ 03:00 am : accumulation rainfall is 13 mm → 04:00 am : reduction of PM10 is more than 95%
accumulation rainfall of 10 mm or less: small reduction in PM10.
accumulation rainfall of 10 mm and more: strong reduction effect.
The accumulated rainfall for 2~3 hours is effective in reducing PM10 even if it is 4mm. This means that precipitation duration plays an important role in reducing PM10.
Graph located on left, divided by 24:00: less amount of rainfall but the duration is longer than the right > PM10 is relatively low
Graph located on the right: large amount of rainfall but the duration is short > PM10 is relatively high

[Fig 2. PM10 reduction rate according to accumulation rainfall]

Accumulation rainfall for 1 hour: 4mm → Reduction rate : 0.55
For 2 hours: 4mm → Reduction rate: 0.7
For 3 hours: 13mm → Reduction rate: 0.95
For 5 hours: 31.5mm → Reduction rate: 0.85 (Since the concentration of PM10 was formed low from the beginning, the reduction rate is also lower than that of 3 hours.)

Paper2 : The Washing Effect of Precipitation on PM10 in the Atmosphere and Rainwater Quality Based on Rainfall Intensity

: This paper deals with the impact of precipitation intensity on particular matter and the resulting rainwater quality. The content of rainwater quality will not be addressed because it does not have much relevance to our team's hypotheses and analysis.

Target period : a total of 6 rainfalls from March to July 2020
Target place : Busan, South Korea

[Heavy rain : 4/17, 6/29, 7/27]

: (Rain intensity ≥ 7.5 mm/h) → (PM10 reduction efficiency ≥ 60%)

[April 17] maximum rain intensity : 8 mm/h, PM10 reduction efficiency: 62.8%

[June 29] maximum rain intensity : 22.5 mm/h, PM10 reduction efficiency: 64.8%
[July 27] maximum rain intensity : 8.5 mm/h, PM10 reduction efficiency: 75.4%

[Light rain : 3/9, 5/2, 7/30]

: (Rain intensity ≤ 5 mm/h) → (PM10 reduction efficiency ≤ 40%)

[May 2] maximum rain intensity: 2.5 mm/h, PM10 reduction efficiency: 28.7%

Paper3: A Study for Characteristics of Fine Particulate Matter and Atmospheric Stagnation Considering Elevation and Backward Trajectory

: Contrary to the initial hypothesis that the concentration of particulate matters will decrease when it rains, the actual analysis confirmed that there are exceptional cases where the concentration increases after rain. Our team thinks the reason is 'atmospheric congestion'. Therefore, we will address only the 'atmospheric congestion' mentioned in the paper.

"Atmospheric congestion" means the flow of air, or wind, slows down. Here, the wind is a vertical wind. The atmosphere is divided into a "boundary layer" where air pollutants generated near the surface are trapped and a "free atmosphere" above it. In summer, when the sun is strong, heated air near the ground mixes up and down well and the boundary layer rises to an altitude of 2km. But in winter, the atmosphere stabilizes as the ground cools, which makes the boundary layer lower. According to an analysis by the National Institute of Environmental Research, this layer in winter has recently been lowered to around 200m. Therefore, fine dust levels are generally higher in winter than in summer. In addition, when placed in the center of high atmospheric pressure, the horizontal wind stops, leaving the air pollutant trapped in a "congestion". While the main cause of high concentrations of fine dust is "atmospheric congestion," it is the "diffusion of the atmosphere" that resolves it. If the air pressure gap widens away from the center of high pressure, the air flow becomes stronger and the concentration of fine dust decreases.

Temperature range where PM2.5 high concentration cases occur frequently: 0.2~11.8°C, 18.0~22.3°C.
0.2~11.8°C: Temperatures from late fall (October) to early spring (April)
18.0~22.3 °C: Temperatures in May, June and September.
Humidity range in which PM2.5 high concentration cases occur frequently: 66–94%.
Wind speed with frequent PM2.5 high concentration cases: 1.8 m/s or less