Air pollution in Southeast Asia is a serious issue, especially during the dry season when smoke from fires and human-made emissions significantly worsen air quality. To better understand the causes, the ASIA-AQ campaign collected air quality data across the region using aircraft, satellites, and ground stations.

In this study, we used a chemical transport model (CMAQ) to simulate air quality and track where it comes from. We tested different combinations of emissions data, including fire and anthropogenic emissions, and compared our results with ASIA-AQ measurements. We also used a tool called ISAM (Integrated Source Apportionment Method) to look at source contributions from different regions and activities.

Our results show that smoke from fires (biomass burning) was the main cause of fine particle pollution (PM2.5) and also strongly affected ozone levels during March 2024. The highest pollution was found in Myanmar, Laos, and Northern Thailand, especially from March 16–18. In countries like Cambodia and Laos, most pollution came from local sources, while other areas like Eastern Thailand and East Malaysia were more affected by pollution from neighboring countries.

These findings help us understand where air pollution comes from and can guide efforts to improve air quality both locally and across borders.