Prescribed burn related increases of population exposure to PM2.5 and O3 pollution in the southeastern US over 2013–2020

Ambient air quality across the southeastern US has improved substantially in recent decades. However, emissions from prescribed burns remain high, which may pose a substantial health threat. We employed a multistage modeling framework to estimate year-round, long-term effects of prescribed burns on air quality and premature deaths. The framework integrates a chemical transport model with a data-fusion approach to estimate 24-h average PM_2.5 and maximum daily 8-h averaged O₃ (MDA8-O₃) concentrations attributable to prescribed burns for the period 2013-2020. The Global Exposure Mortality Model and a log-linear exposure-response function were used to estimate the premature deaths ascribed to long-term prescribed burn PM_2.5 and MDA8-O₃ exposure in ten southeastern states. Our results indicate that prescribed burns contributed on annual average 0.59 ± 0.20 µg/m³ of PM_2.5 (∼10 % of ambient PM_2.5) over the ten southeastern states during the study period. On average around 15 % of the state-level ambient PM_2.5 concentrations were contributed by prescribed burns in Alabama (0.90 ± 0.15 µg/m³), Florida (0.65 ± 0.19 µg/m³), Georgia (0.91 ± 0.19 µg/m³), Mississippi (0.65 ± 0.10 µg/m³) and South Carolina (0.65 ± 0.09 µg/m³). In the extensive burning season (January-April), daily average contributions to ambient PM_2.5 increased up to 22 % in those states. A large part of Alabama and Georgia experiences ≥3.5 µg/m³ prescribed burn PM_2.5 over 30 days/year. Additionally, prescribed burns are responsible for an average increase of 0.32 ± 0.12 ppb of MDA8-O₃ (0.8 % of ambient MDA8-O₃) over the ten southeastern states. The combined effect of prescribed burn PM_2.5 exposure, population growth, and increase of baseline mortality over time resulted in a total of 20,416 (95 % confidence interval (CI): 16,562-24,174) excess non-accidental premature deaths in the ten southeastern states, with 25 % of these deaths in Georgia. Prescribed burn MDA8-O₃ was responsible for an additional 1,332 (95 % CI: 858-1,803) premature deaths in the ten southeastern states. These findings indicate significant impacts from prescribed burns, suggesting potential benefits of enhanced forest management strategies.