Past and recent changes in the pollution characteristics of PM10 and SO2 in the largest industrial city in South Korea

Abstract

PM10 and SO2 are major air pollutants in Ulsan, the largest industrial city in South Korea. The purpose of this study was to evaluate the effectiveness of pollution reduction policies by comparing the pollution characteristics of PM10 and SO2 between 2012 and 2020. The concentrations of PM10 and SO2 have substantially decreased over time. Local industry was the primary driver of SO2 levels, whereas various sources were associated with PM10 levels. In 2012 and 2020, the spatial distributions of SO2 were similar, with hot spots around petrochemical and nonferrous industrial complexes, whereas the sources of PM10 differed between the two years. Although industrial emissions of PM10 decreased from 2012 to 2020, the concentrations derived from an air dispersion model were slightly higher in 2020 due to changes in both wind patterns and the strength of the emission sources. In contrast, modeled SO2 levels were higher in 2012 than in 2020 due to greater emissions in 2012. Eastern and northeastern China were identified as potential source areas for the long-range atmospheric transport of both PM10 and SO2, though its influence was significantly lower in 2020. A comparison of the PM10 and SO2 concentrations predicted by a random forest model and the measured concentrations indicates that government policies have been effective in reducing the emissions and ambient air concentrations of both pollutants. In conclusion, this study demonstrates that local industry remains a significant contributor to air pollution in Ulsan despite the effects of governmental policy. Furthermore, as the influence of external sources weakens, there is a pressing need to strengthen the management of local sources to effectively mitigate air pollution in Ulsan.