Abstract
In March 2020, the average concentration of PM2.5 in Seoul decreased by 44% compared to that in March 2019 (from 45 µg m–3 to 25 µg m–3). In this study, the synoptic and local meteorological conditions during the period with reduced PM2.5 concentrations were analyzed. The synoptic meteorological conditions during March 2020 show a common characteristic of strong zonal flow and winds. Therefore, air circulation was active and meteorological conditions were unfavorable to long-range transboundary transport. Local meteorological conditions such as wind and turbulent motion at the surface were sensitive to PM2.5 concentrations. Our analyses indicate that the greatly reduced PM2.5 concentrations were mainly influenced by synoptic rather than local conditions. Decreased demand for heating of buildings due to warmer temperatures in March 2020, the economic slowdown following the outbreak of COVID-19, and the implementation of guidelines aimed at controlling particulate matter (PM) were other important causes of reduced PM2.5 emissions. A decrease in long-range transboundary transport contributed to the reduced PM2.5 concentrations.
Highlights
Seoul, the capital city of South Korea, is a megacity with approximately 10 million inhabitants in an area of 605 km2
The results of our analysis indicate that the reduction in PM2.5 concentrations in March 2020 during the COVID-19 epidemic was mainly influenced by synoptic meteorological conditions
We estimate that the PM2.5 concentrations during March 2020 were reduced to approximately 9 μg m–3 by the synoptic meteorological conditions around the northern and eastern areas of the Korean Peninsula
Summary
The capital city of South Korea, is a megacity with approximately 10 million inhabitants in an area of 605 km. The terrain around Seoul is dominated by the complex terrain of the surrounding mountains, which range in elevation from 600 m to 900 m, except to the west. Studies have shown that the concentration of particulate matter with ≤ 2.5 μm diameter (PM2.5) is affected by local emissions, meteorological conditions, and long-range transport processes (Park et al, 2019, 2020). The first case of COVID-19 in South Korea was confirmed on January 20, 2020 (KCDC, 2020a). On February 23, 2020, the Korean government raised its COVID-19 alert to the highest level of “red” in order to strengthen the overall response system (KCDC, 2020b)
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