Long-Term Trend of the Levels of Ambient Air Pollutants of a Megacity and a Background Area in Korea

It is imperative to understand the changes of the levels of air pollutants in Northeast Asia with respect to the changes of the emissions of air pollutants. In this study, we analyzed long-term trends of both the chemical composition of fine particles and gaseous species in Seoul, a megacity, and Baengnyeong Island, a background area located in the Yellow Sea of Republic of Korea (South Korea) from 2012 to 2019. Long-term changes of the concentrations of air pollutants were analyzed using the Mann–Kendall trend test and Sen’s slope. Since the SO2 emissions in this region have been significantly reduced during last decade, NO3− has become the major species of fine particles instead of SO42−. Seoul and Baengnyeong Island are rich in NH4+ in the atmosphere, and due to the SO2 emission reduction, the balance of ammonia–nitric acid–sulfuric acid has been changed, and the concentration of NO3− has increased. This trend is more obvious in Baengnyeong Island than Seoul due to the lower local emissions in Baengnyeong Island. As a result of this study, it is possible to confirm that concentrations of air pollutants and the majority of aerosols affecting PM2.5 concentrations in Northeast Asia have changed according to the changes in emissions in this region.