Associations between PM_2.5 from prescribed burning and emergency department visits in 11 Southeastern US states

Longer, more severe wildfire seasons are becoming the norm in fire-prone areas. Prescribed burning is a tool used to mitigate wildfire spread. However, prescribed burning also contributes to air pollution, including PM_2.5 (particulate matter with aerodynamic diameter <= 2.5 µm). While the health impacts of wildfire smoke (WFS) are well-studied, relatively less is known about the effects of prescribed fire smoke (PFS). Our study leverages healthcare claims available for residents of 11 Southeastern US states (2013-2021) to investigate the health impacts associated with PFS. We used a chemical transport model (CTM) and data fusion-based method to estimate county-level outdoor PFS-specific PM_2.5 concentrations and employed a time-stratified case-crossover design to quantify the relative risk of emergency department (ED) visits associated with PM_2.5 levels lagged 0-3 days. Models adjusted for non-prescribed fire PM_2.5 and O₃, temperature, humidity, and holidays. We also examined how relative risks varied across population subgroups. PFS-specific PM_2.5 was associated with a relative risk of ED visits for non-external causes (1.01, 95 % confidence interval (CI): 1.01, 1.02) comparing 4.3 µg/m₃ (95th percentile) versus 0 µg/m³, upper respiratory infections (1.04, 95 % CI: 1.01, 1.07), and ischemic heart disease (1.06, 95 % CI: 1.01, 1.11). We did not observe an increased risk for overall respiratory outcomes, asthma, or COPD, which differs from published WFS findings. Relative risks varied across outcomes and modestly across population subgroups defined by age and markers of social vulnerability. However, after correcting for multiple comparisons, these differences were not significant. Some findings differed from associations previously reported elsewhere for WFS, highlighting the need for direct comparisons of the health impacts of WFS versus PFS for evaluating safety of prescribed burning as a fire management tool.