Analysis of High-Concentration PM2.5 Episodes during Winter 2019–2020 in Seoul, Korea

PM2.5 is a WHO-designated first-class carcinogen and coping with high-concentration situations with high human risk is becoming more important. In particular, Korea has a high concentration of PM2.5 in winter due to its geographical characteristics, which can be largely divided into foreign inflows and domestic atmospheric stability. To determine this, wind patterns and air pressure data were analyzed representatively and episodes about high concentration phenomena were classified. In this study, high-concentration PM2.5 episodes, where the daily average PM2.5 concentration in Seoul exceeded 35 μg/m3 between October 2019 to March 2020, were analyzed case-by-case. The criteria for the separation of consecutive episodes were established. Then, the designated episodes were classified into four categories based on cause: atmospheric stagnation, combination of causes, penetration from abroad, and accumulation. To identify the causes of the episodes, wind direction, wind speed data, wind roses, and air quality forecast modeling data obtained from “Air Korea” were studied. Fifteen episodes were identified and analyzed and each were given a classification type. Furthermore, the phenomenon of high-concentration episodes was summarized after detailed individual analysis of the episodes. As a result of case analysis, just before there was an inflow from abroad due to strong wind speed, a characteristic of low PM2.5 concentration of air quality as a kind of cleaning effect could be found. In addition, alarm-level PM2.5 concentrations of 75 μg/m3 or higher were often made by external inflow. This will contribute towards identifying the main causes of high PM2.5 concentration episodes in Korea when it is applied over a longer time period.