Exposure-crossover observations of air pollution after large-scale fireworks in two Korean megacities, Seoul and Busan: Empirical evidence toward sustainable festivals.

Firework burning can significantly contribute to emissions of ambient air pollutants such as particulate matters (PM), which might pose serious public health concerns. Nevertheless, environmental research and public health attention to this matter are limited in many countries, particularly in Korea where firework festivals remain popular in megacities. This study aimed to examine temporal and spatial patterns of ambient air pollution during large-scale firework festivals in two megacities of Korea, focusing on each event held in Seoul (the second highest population in the world, as a metropolitan area) and Busan (the second highest population in Korea) in 2023. We used self-matched exposure-crossover design to compare ambient air pollution trends on exposure-event days (firework festival dates) with those on reference days (one week before and after festival dates) to evaluate a sole contribution of firework display. We analyzed data from air quality monitoring stations and visualized spatiotemporal changes in concentrations of air pollutants (i.e., PM, PM, and SO) during the festival period. Analysis of the Seoul festival revealed significant increases in PM and PM concentrations following fireworks, with peaks reaching 320 and 371 μg/m. Similar patterns were observed after the Busan festival, with peak concentrations of 241 and 253 μg/m for PM and PM. These concentrations were 7.4-12.2 times higher than those observed on reference days. Spatiotemporal analysis demonstrated that PM and PM emitted from fireworks dispersed in the direction of wind. In contrast to high increases in PM and PM, SO levels showed light increases after both festivals, with a peak concentration of 4.9 ppb in Seoul and 5.7 ppb in Busan. Considering the estimated attendance of about a million at each festival and the high-density population area around two firework locations, the potential health risk posed by firework-related air pollution is a significant public health concern.