Influence of biomass burning on suburban PM2.5 variability in Nakhon Pathom, Thailand: a multi-scale analysis of fire intensity and atmospheric transport

This study examined the influence of biomass burning on the variability of fine particulate matter (PM 2.5 , aerodynamic diameter ≤ 2.5 µm) at a suburban receptor site in Nakhon Pathom, Thailand, during the dry seasons of 2023 and 2024. Regional transport was characterized using backward trajectory clustering and concentration-weighted trajectory analysis, fire characteristics using satellite-derived fire radiative power, and local source–receptor relationships using time-lagged Spearman correlation stratified by wind direction. Northeasterly transport dominated in both seasons, declining from 57.43% to 47.52% of trajectories, and was the only direction along which biomass burning was consistently associated with PM 2.5 . Local wind measurements, cluster-level regression and lagged correlation converged on this conclusion. Burning within Nakhon Pathom province occurred almost entirely on agricultural land. Biomass burning increased between seasons, with hotspot counts within Thailand inside a 600 km radius rising from 11,949 to 13,728 and fire radiative power per detection unchanged at 3.7–3.8 MW, yet PM 2.5 did not increase. The association between burning and PM 2.5 weakened markedly in 2024, coinciding with a decline in northeasterly conditions at the receptor from 13 of 89 days to 3 of 90 during February–April and significantly higher daily wind speeds (medians 3.30 and 2.68 m/s, p < 0.001). These results indicate that hotspot counts alone are an insufficient proxy for PM 2.5 at this site, and that suburban air quality management must address transport conditions and persistent anthropogenic emissions alongside biomass burning.