Spatial distribution of PM2.5 chemical components during winter at five sites in Northeast Asia: High temporal resolution measurement study

Abstract

The Center for Fine Particle Research Initiative in East Asia considering National Differences (FRIEND) project was launched in 2020 to characterize air pollution in Northeast Asia with effective collaboration. One of the goals of this study is to elucidate the spatiotemporal characteristics of atmospheric aerosols (e.g., PM2.5) in Northeast Asia. To achieve this objective, (1) the chemical speciation of fine particles was measured in high resolution, (2) the physical characteristics of fine particles were also elucidated, and (3) the gaseous and particulate components of the atmospheric aerosols were comprehensively monitored. The first field campaign was conducted from December 15, 2020, to January 15, 2021, and simultaneously monitored five key sites in Northeast Asia: Ulaanbaatar, Mongolia; Beijing, China; Seosan and Seoul, Republic of Korea (Korea); and Noto, Japan. The synoptic weather conditions mainly determined the periods of high PM2.5 mass concentration. During the first high-pollution event, the air over the Northeast Asian region was generally stagnant, and the inland wind speed over China, Korea, and Japan was very low. The PM2.5 mass concentration in Beijing, Seosan, and Seoul had increased simultaneously. Then, the prevailing westerlies in Northeast Asia caused the polluted air mass observed in Seoul to move to the background site in Noto. During the second high-pollution event, the Asian dust phenomenon occurred in the Gobi Desert and moved to all sites. Though the synoptic weather conditions largely determined the trend of the PM2.5 mass concentrations at the five sites, the levels of chemical components in both gaseous and particulate phases were different at each site, reflecting local emission and formation characteristics. Overall, the concentrations of air pollutants were highest in Ulaanbaatar; comparable in Beijing, Seoul, and Seosan and very low in Noto. A common characteristic of the five sites was the high organic aerosol (OA) proportion in fine particles. The chemical components that increased with the PM2.5 mass concentration were OA at Ulaanbaatar, OA and nitrate at Beijing and Seosan, nitrate at Seoul, and sulfate and OA at Noto. Further study directions for each site are discussed.