Trend Analysis of PM2.5 Source Contributions in Seoul and Ulsan, South Korea (2016-2022)

PM_2.5, identified as a health-hazardous substance and classified as a Group 1 carcinogen by the International Agency for Research on Cancer in 2013, poses significant risks to public health.  To combat these risks, the South Korean government established the ambient air quality standard for PM_2.5 mass concentration through the Air Quality Preservation Act in 2013, initially implemented in Seoul and expanded nationwide in 2015. Since December 2019, the Seasonal Management Program has targeted major PM_2.5 sources during winter (December–March), a period of frequent high concentration events. While these measures initially achieved notable reductions, the downward trend in PM_2.5 mass concentration has slowed in recent years. In 2022, South Korea recorded an annual average PM_2.5 mass concentration of 18.3 μg/m³, exceeding the national air quality standard of 15 μg/m³.

This study aimed to analyze long-term trends in PM_2.5 source contributions using the meteorologically adjusted Dispersion-Normalized Positive Matrix Factorization (DN-PMF) model. Hourly monitoring data from 2016 to 2022, provided by the National Institute of Environmental Research (NIER), were analyzed for two sites: Seoul, the capital city, and Ulsan, an industrial hub. The dataset included PM_2.5 mass concentrations, carbonaceous components (OC, EC), ionic species (NO₃^-, SO₄^2-, Cl^-, NH₄⁺, Na⁺, K⁺), and trace elements (S, K, Si, Al, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Ba, Pb). The Conditional Bivariate Probability Function (CBPF) model was utilized to identify the direction of local sources. Comprehensive trend analyses, including Theil-Sen regression, Seasonal Trend Decomposition based on LOESS (STL), and Piecewise Regression, were conducted to assess variations in source contributions over time.

This study resolved 10 sources through PMF modeling at each site: secondary sulfate, secondary nitrate, motor vehicles, biomass burning, incineration, oil combustion, coal combustion, soil, industry, and sea salt. Temporal variations revealed differing trends between the two sites. In Seoul, PM_2.5 mass concentrations consistently decreased, with significant reductions in contributions from incineration, oil combustion, and industry sources. In contrast, Ulsan exhibited a more rapid decline in PM_2.5 mass concentrations particularly for biomass burning and oil combustion sources. Addressing secondary sulfate and mobile sources remains critical for further air quality improvements.

This study provided essential receptor-based evidence to support the development of future air quality management strategies, addressing both local and transboundary PM₂.₅ sources effectively.

Acknowledgment

This research was supported by “Study on the analysis of medium- and long-term factors affecting PM_2.5 emission changes” funded by the National Air Emission Inventory and Research Center of the Ministry of Environment under grant, South Korea. This work was supported by the National Institute of Environmental Research (NIER) of the Ministry of Environment under grant, South Korea No. NIER-2021-03-03-001. This research was supported by the Particulate Matter Management Specialized Graduate Program through the Korea Environmental Industry & Technology Institute (KEITI) funded by the Ministry of Environment (MOE).