THE PARTICULATE MATTER & PRECIPITATION
1)
2/12(There was precipitation)
Average daily concentration of particulate matter: 63 μg/m³
2/13(The next day)
Average daily concentration of particulate matter: 90 μg/m³
The accumulated precipitation from 18:00 to 21:00 on the 12th was about 4.4 mm,
exceeding precipitation standard needed for the PM reduction suggested in the paper 2.
Therefore, there is a possibility of PM reduction effect. The concentration of PM steadily decreased from 12 p.m. on February 12 to 1 a.m. on 13 with continuous rain.
However, PM levels continued to rise from 2 a.m. on February 13.
The average daily concentration of PM increased from 63 μg/m³ on February 12 to 90 μg/m³ on 13.
The reasons for this can be found in domestic atmospheric congestion and the inflow of PM from abroad.
According to paper 3, the rainfall intensity is less than 5 mm/h, so PM10 has a reduction effect of less than 40%. In addition, conditions are formed for atmospheric congestion when wind speeds are less than
1.8 m/s over time. The paper is based on PM2.5 high concentration cases, and the lack of prior studies on the correlation between atmospheric congestion and wind speed caused by PM10 made us to adopt
the paper as analysis tool.
According to the data on February 12, PM levels were high in the morning due to accumulation of previous day's PM by atmospheric congestion, and the PM concentration gradually decreased due to precipitation in the afternoon. It is believed that the concentration of PM in the early morning of February 13 will increase as some previous PM remains and PM generated in Korea will be added due to the atmospheric congestion in the afternoon.
In fact, the concentration of PM in the morning of the 13th tended to increase,
which is thought to be due to the inflow of PM from foreign countries and domestic PM accumulated
due to atmospheric congestion.
1)
5/9(There was precipitation)
5/10(There was precipitation & A day after precipitation)
5/11(A day after precipitation)
Analysis of Particulate Matter and Precipitation in February, March, April and May 2020
PM and precipitation in Seoul were analyzed on a daily basis in February, March, April and May 2020. The following indicated days of precipitation and the day after precipitation:
Based on the paper introduced earlier, not only the total daily rainfall, but also the rainfall intensity and accumulated rainfall are factors that directly affect the concentration of PM.
1. February
February had precipitation on 4, 12, 15, 16, 17, 21, 22, 25, 28, and 29.
The date marked in red is when PM did not decrease on the day after the rain.
According to the table, despite the rain on the 12th and 29th, PM levels rose on the 13th and March 1st.
The results were contrary to the initial hypothesis that "if it rains, the concentration of PM will decrease."
To analyze the reason for these results, the average concentration of PM per hour, precipitation per hour, and
wind speed per hour were investigated on February 12th and 13th, February 29th and March 1st.
2)
2/29(There was precipitation)
Average daily concentration of particulate matter: 26 μg/m³
3/1(The next day)
Average daily concentration of particulate matter: 57 μg/m³
Looking at the hourly precipitation data on February 29, there is no case of the rainfall per hour is more than 10 mm or 4 mm of accumulated precipitation if the duration is more than 3 hours.
It is difficult to see the effect of reducing PM caused by precipitation.
On February 29, due to smooth atmospheric diffusion, PM levels are low.
However, in night, PM flowed in from outside the country. Because of airflow collection and convergence air current in central regions, PM levels in Korea increased on March 1.
2. March
March had precipitation on 1, 10, 13, 26, and 27.
According to the table, despite the rain on the 13th, PM levels rose on the 14th.
The reasons for this were analyzed in the same way as in February.
1)
3/13(There was precipitation)
Average daily concentration of particulate matter: 32 μg/m³
3/14(The next day)
Average daily concentration of particulate matter: 46 μg/m³
Looking at the hourly precipitation data on March 13, there is no case of the rainfall per hour is more than 10 mm or 4 mm of accumulated precipitation if the duration is more than 3 hours.
It is difficult to see the effect of reducing PM caused by precipitation.
On March 13, PM levels are "normal" due to smooth atmospheric diffusion.
On the other hand, on March 14, there is a significant increase in the concentration of PM at night
due to the combination of atmospheric congestion in the morning and inflow of PM from abroad in the afternoon.
3. April
April had precipitation on 17, 19, and 20.
According to the table, despite the rain on the 20, PM levels rose on the 21.
The reasons for this were analyzed in the same way as in February.
1)
4/20(There was precipitation)
Average daily concentration of particulate matter: 19 μg/m³
4/21(The next day)
Average daily concentration of particulate matter: 33 μg/m³
Looking at the hourly precipitation data on April 20, there is no case of the rainfall per hour is more than
10 mm or 4 mm of accumulated precipitation if the duration is more than 3 hours.
It is difficult to see the effect of reducing PM caused by precipitation.
On April 20, the atmosphere was clean due to smooth atmospheric diffusion, but yellow dust originated in northern China in this afternoon.
Considering the speed and pressure of the northwest wind, it can be expected to reach the country within a day.
As expected, yellow dust from northern China flowed into Seoul on the 20, and at the same time, additional yellow dust from northeastern China flowed in on the 21.
For this reason, PM10 concentration was temporarily high during the day of the 21.
However, since the late afternoon, the atmosphere has been resolved by smooth atmospheric diffusion,
and the atmosphere has generally been clean.
4. May
May had precipitation on 9, 10, 11, 16, and 24.
According to the table, despite the rain on the 9th, 10th, 16th, and 24th, PM levels rose on the next days each.
The reasons for this were analyzed in the same way as in February.
Average daily concentration of particulate matter: 16 μg/m³
Average daily concentration of particulate matter: 37 μg/m³
Average daily concentration of particulate matter: 98 μg/m³
The concentration of PM increases compared to the previous day after the rain.
According to the hourly precipitation data on May 9, it rained from 0 to 17 without stopping.
The resulting accumulated rainfall is about 23.7 mm, exceeding the standard suggested in the paper 2 (precipitation of more than 4 mm lasting 3 hours).
So it is likely to have a PM reduction effect due to precipitation.
Because the rainfall intensity is less than 5 mm/h, the reduction effect of PM10 is less than 40%.
It rained all day, and the concentration of PM steadily decreased from 9th to 10th dawn.
However, the concentration of PM tends to increase from the afternoon of May 10.
Considering the wind speed, there would have been no atmospheric congestion on both May 9 and 10. Nevertheless, the PM concentration increases in the afternoon of May 10.
The reasons are inflow of foreign PM, yellow dust originated in northern Mongolia and the Gobi Desert
on the morning of May 9 which flows into Seoul from late afternoon May 10.
Looking at the hourly precipitation data on May 10, there is no case of the rainfall per hour is more than
10 mm or 4 mm of accumulated precipitation if the duration is more than 3 hours.
It is difficult to see the effect of reducing PM caused by precipitation.
PM began to rise gradually in the afternoon of May 10 and is showing a large figure in the afternoon of May 11.
Given wind speed conditions of 10 and 11, atmospheric congestion would not have occurred.
Then why did the concentration of PM on the 11 increase significantly compared to the 9 and 10?
First of all, the precipitation on the 10 and 11 decreased significantly compared to the 9.
In addition, yellow dust that originated on the 9 landed in Seoul on the afternoon of the 10, and additional yellow dust originated in northeastern China and the Inner Mongolia Plateau on the afternoon of the 11. On top of that, the inflow of PM from abroad also affected.
2)
5/16(There was precipitation)
Average daily concentration of particulate matter: 29 μg/m³
5/17(The next day)
Average daily concentration of particulate matter: 44 μg/m³
Looking at the hourly precipitation data on May 16, there is no case of the rainfall per hour is more than 10 mm or 4 mm of accumulated precipitation if the duration is more than 3 hours.
It is difficult to see the effect of reducing PM caused by precipitation.
Considering wind speed conditions, atmospheric congestion is likely to have occurred because wind speeds below 1.8 m/s continued from 2 a.m. to 4 p.m. on May 16.
PM generated in Korea has accumulated due to atmospheric congestion, and PM tends to gradually increase in the afternoon of the 16th. From midnight of the 16th to 17th, PM generated in Korea is accumulated due to atmospheric congestion caused by wind speed weakening, showing a tendency to gradually increase the concentration of PM.
3)
5/24(There was precipitation)
Average daily concentration of particulate matter: 29 μg/m³
5/25(The next day)
Average daily concentration of particulate matter: 45 μg/m³
According to the hourly precipitation data on May 24, it rained continuously from 3 a.m. to 9 a.m.
The resulting accumulated rainfall is about 14.5 mm, exceeding the standard suggested in the paper 2 (precipitation of more than 4 mm lasting more than 3 hours). This exceeds the standard level of precipitation needed for PM reduction suggested in the paper 2, so there is a possibility of PM reduction due to precipitation.
The rainfall intensity is 7.7 mm/h around 7 a.m. on the 24th.
Since the rainfall intensity is heavy rain with 7.5 mm/h or higher, PM10 reduction efficiency is over 60%. On the 24th, PM levels are not high due to smooth atmospheric diffusion and precipitation.
Then why did the concentration of PM increase on the 25th?
According to the wind speed data on the 25th, it is highly likely that the wind speed of 1.8 m/s or
less lasted for several hours in the morning, causing atmospheric congestion.
It can be interpreted that the concentration of PM in Korea gradually increased on the afternoon of the 25th due to such atmospheric congestion.