Environmental policies corresponding to “fine particulate matter (PM2.5)” typically regulate economic activity in attempts to reduce anthropogenic emissions. As these regulations often inconvenience citizens to a certain extent, it is necessary to evaluate their impacts before they are implemented. We developed an evaluation model to assess the impacts of these regulations on surface PM2.5 in Seoul using a meteorological model and air quality models. We attempted to account for the impacts of five-year meteorological variability on the effectiveness of the regulations. 
It has been reported that air quality in Seoul has improved since the late 1990s due to various efforts by the national and local governments. However, PM2.5 in Seoul has fallen under the domestic annual PM2.5 standards over the past five years. We examined the monthly and hourly averages of PM2.5 using the urban air quality monitoring network in Seoul from January 2015 to March 2020. We found that high levels of PM2.5 occurred in wintertime during this period. Specifically, during the wintertime, the average PM2.5 levels in March were the highest in 2017 and 2019.
We investigated the main factors affecting the levels of PM2.5 are foreign and domestic air pollutant emissions and meteorological phenomena. Among meteorological phenomena, wind greatly affects the distribution of PM2.5. In this study, we analyzed the variability of PM2.5 in Seoul and selected Chinese cities according to the wind characteristics, and our results showed that the wind direction and wind speed substantially affected the surface levels of PM2.5 in these cities.
To forcus on the influence of meteorological phenomena, we conducted simulations of five-year wintertime PM2.5 using the constant anthropogenic emission inventories in East Asia. We found that the differences in monthly-averaged PM2.5 in Seoul were as high as 13 ㎍/㎥; it was confirmed that these differences can offset the effects of the regulations. We also showed that the assessment of PM2.5 regulation can vary between years due to the different meteorological conditions.
This study suggests that weather variability should be accounted for when assessing the impact of PM2.5 regulations. We also described several limitations in this study. To overcome these limitations, it is necessary to elaborate on the meteorological model and update domestic and foreign emissions. We concluded that the method of assessing the policy implementation rate and a method of verifying this method are necessary to improve the quality of the model developed in this study.