Establishing PM2.5 conversion factors for South Korea at provincial level

Abstract

As air pollution remains a pressing issue in South Korea, identifying appropriate emission reduction measures to improve air quality remains a major challenge. Given that the 17 administrative provinces in South Korea have distinct emissions footprints, a uniform nationwide emissions-reduction measure could be ineffective. Therefore, this study calculates province-specific control measures to improve the overall air quality in the country. The conversion factor (CF) is a proposed metric that quantifies the reduction in PM2.5 per metric ton (MT) of emission reduction (in μg/m3/MT). For this work, using the conventional brute-force method to determine the impacts of reducing emissions from the 17 provinces on the national PM2.5 level becomes computationally demanding. This problem led us to utilize the sensitivity calculations from the CMAQ-DDM model to determine the conversion factors. The CFs were calculated in this study by dividing the PM2.5 sensitivities from the CMAQ-DDM model by the provincial emissions. The provincial CFs for NOx, SO2, NH3, benzene, toluene, and xylene emissions across four seasons were calculated. The results revealed stark differences in the CFs across the 17 provinces, suggesting the need for province-specific emission reduction actions. Based on these results, policymakers are urged to shift their focus to NH3 rather than NOx and SO2, as NH3 was found to be the most effective control species for reducing PM2.5. In particular, reducing NH3 in rural areas was identified as the most efficient action to abate national levels of PM2.5. For example, the reduction of a metric ton of NH3 in rural Gangwon-do can result in decreases in national PM2.5 of 5.5 × 10−2, 3.2 × 10−2, 1.8 × 10−2, and 5.0 × 10−2 μg/m3, while in urban Seoul, the decreases are only 6 × 10−4, 1.1 × 10−3, 6 × 10−4, and 1.3 × 10−3 μg/m3 during winter, spring, summer, and fall, respectively. © 2026