Spatiotemporal differences on the real-time physicochemical characteristics of PM2.5 particles in four Northeast Asian countries during Winter and Summer 2020–2021

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Northeast Asian countries have suffered from high concentration of the particulate matter (PM2.5). However, the lack of simultaneous real-time measurements on the PM2.5 physicochemical characteristics in the different Northeast Asian countries has retarded to understand and mitigate high PM2.5 air pollution in the continent. In this study, two simultaneous monitoring campaigns were conducted at five supersites in Northeast Asia by deploying same methods using real-time instruments during the winter and summer 2020–2021. Through the campaigns, several high PM2.5 events were observed in the same periods in the winter among some countries, which were related to the weather conditions. However, the formation and growth trends of PM2.5 were largely different among the countries, affecting on the spatiotemporal differences of PM2.5 physicochemical characteristics with local emission. PM2.5 mass concentration (CPM2.5) measured in Ulaanbaatar (Mongolia) in the winter showed the highest value due to primary emission by fuel-combustion, but lowest in the summer. In contrast, CPM2.5 in Noto (Japan) was lowest during the two campaigns among the countries as a background measurement site. Compared to Seosan and Seoul (Republic of Korea), Beijing (China) showed lower total number of PM2.5 particles during the winter campaign. However, the PM2.5 particles were grown larger in Beijing than the two Korean sites, resulting similar average CPM2.5 with the Korean sites in the winter. During the CPM2.5 increased, the real-time concentration of the nitrate increased simultaneously and became the dominant PM2.5 constituent, which was commonly observed at Seoul, Seosan and Beijing. However, the seasonal changes of the PM2.5 chemical constituents were different depending on the sites, causing the different seasonal changes of CPM2.5. Otherwise, sulfate and organics significantly contributed to the CPM2.5 (>80%) at Noto, where the CPM2.5 was generally <35 μg/m3 with little amount of nitrate.