Seasonal PM Management: (II) How Low PM2.5 Concentration in South Korea can be Achieved?

We quantitatively estimated PM2.5 (Particulate Matter of 2.5 & mu;m or less in diameter) reduction potential of domestic emissions in South Korea during the 2nd Seasonal PM Management (SPM; December 2020 -March 2021). A set of threedimensional air quality model simulations utilizing Community Multi-scale Air Quality (CMAQ) based on the Clean Air Policy Support System 2018 and Satellite Integrated Joint monitoring of Air Quality version 1 emissions inventories (EIs) were applied. Foreign or domestic emissions were reduced by 50% or 100% in turn to estimate the emission impacts in different simulations and/or adjusting approaches. Depending on choice on the perturbation rate and emission source area, EI-based domestic emission impacts ranged from 10.6 to 13.5 & mu;g/m3 (42 -54%) for the study period. The domestic emission impact estimated from a 100% reduction of national emissions was 2.9 & mu;g/m3 higher than that from a 50% reduction. It implies that appreciable nonlinear relationship exists between domestic emissions and the PM2.5 concentrations. Meanwhile, the EI-based PM2.5 simulations were underestimated by 7% in China and overestimated by 4% in South Korea, respectively. Considering the simulation uncertainty, domestic and foreign impacts were adjusted based on the PM2.5 observations. After the adjustment, the domestic impacts were assessed to 8.6 -13.0 & mu;g/m3 that can be interpreted as the maximum domestic PM2.5 reduction potential. When a 100% reduction of domestic emissions was assumed, the national PM2.5 concentration during the SPM barely satisfied the annual average air quality standard level (15 & mu;g/m3). On the other hand, it was predicted that simultaneously reductions of domestic and foreign emissions by 50% lowered the PM2.5 concentration in South Korea during the SPM to 13.0 & mu;g/m3. Considering that it is realistically impossible to reduce total domestic emissions (i.e., 100%), international cooperation among neighboring countries is imperative to achieve the target PM2.5 concentration in South Korea.