Enhancing the methodology for calculating emission reductions in air quality policies

This study improves the calculation methods for emission reduction of individual policies and policy sets and validates the enhanced methodologies through scenario analysis experiments. First, to ensure that the policy's rule penetration does not exceed 100%, emission sources with excessive policy applications are classified and their reductions are adjusted accordingly. Second, each policy is applied sequentially and adjusts target emissions to reflect prior policy reductions. This prevents overestimation of the total reduction amount, and the reduction for each policy is calculated based on the adjusted value and then summed to obtain the total reduction for the policy set. We selected air pollutants, NO x , SO x , PM 2.5 , and VOCs to calculate reductions and analyzed the improvement effects through experimental scenarios in Korea's Seoul Metropolitan Area (SMA). According to the comparison between the Clean Air Policy Support System (CAPSS) inventory and the results of this study for 2019, NO x exhibited a difference of 6.8% in the non-improvement scenario, which was reduced to 0.1% after the improvement. The differences in SO x , PM 2.5 , and VOC decreased from 5.0% to 2.4%, 14.1%–7.9%, and 55.8%–30.6%, respectively. When comparing the NO x emission change rates from 2015 to 2018 with Globemission and CAPSS-KU inventories, the differences in the non-improvement scenario were 8.9%p and 9.6%p, respectively, but decreased to 4.4%p and 5.2%p after the improvement. Thus, existing policy research methodologies overestimate policy effects. This study is expected to contribute to a more accurate analysis of policy effects and provide useful data for establishing air quality policies. • Potential overestimation in the current policy evaluation process was indicated. • A refined method was developed for more accurate and effective evaluations. • The improved method provides a more accurate estimation of policy reductions.