Traffic congestion and air pollution: Empirical evidence before/after COVID-19 in Seoul, Korea

Severe traffic congestion leads to toxic levels of air pollution. We attempt to explore how traffic congestion affects air pollution, especially PM10 and PM2.5, by focusing on the city of Seoul, Korea, which is one of the largest cities in the world and is plagued by severe traffic congestion. We employ a fixed-effect panel model with various datasets, including air pollution, travel speed, and weather conditions. The findings show that traffic congestion adversely affects air quality by increasing the concentration of PM10 and PM2.5. In particular, the impact of traffic congestion on PM10 and PM2.5 was 1.2 times and 1.7 times greater during the COVID-19 period than during the non-COVID-19 period, respectively. In addition, an increase in one unit of RCI is associated with 0.4 μg/m3 increase in PM10 during the peak hours, but 6.7 μg/m3 increase in PM10 during the non-peak hour because of the increased traffic of trucks and motorcycles induced by increased online shopping. To mitigate air pollution, it is suggested that not only reducing vehicle use, but also minimizing traffic congestion is important.