O3 Increment from Prescribed Burns: Implications for Air Quality and Public Health in the Southeastern United States

Abstract

Prescribed fire (PF) is extensively practiced across the southeastern United States (US) to maintain fire-adapted ecosystems and reduce wildfire risk. However, PF emits substantial quantities of ozone (O3) precursors that can elevate ground-level O3 through photochemical reactions. This study quantified PF contributions to ambient O3 and associated premature mortality across 12 southeastern US states from 2013 to 2021 using the Community Multiscale Air Quality (CMAQ) model at 12-km resolution. Model results were calibrated through data fusion with surface observations, and sensitivity to spatial resolution was examined with a nested 4-km simulation over Georgia. At 12-km resolution, contribution from PFs to daily maximum 8-h average O3 (MDA8 O3) concentrations averaged to 0.34 ± 0.12 ppb across the region, accounting for ∼0.9% of ambient levels. The PF contribution to daily maximum 1-h average O3 (MDA1 O3) averaged to 0.46 ± 0.18 ppb or ∼1.1% of ambient MDA1 O3. At state level, highest annual average PF-MDA8 O3 (0.59 ± 0.14 ppb) and PF-MDA1 O3 (0.84 ± 0.22 ppb) were estimated in Georgia. Seasonal peaks (January–April) coincided with higher burning activity, with PF-MDA1 O3 exceeding 1.0 ppb in Georgia, Alabama, Florida, and South Carolina. During the nine-year period, PF-related MDA8 O3 exposure (short-term + long-term) associated 8925 (95% CI: 6273–11,567) premature all-cause deaths, with 62% linked to long-term exposure. Florida (2618), Georgia (1465), and North Carolina (910) experienced the highest absolute mortality burdens. The 4-km resolution model performed better than the 12-km model in estimating MDA8 O3 concentrations. In Georgia, the 4-km simulation estimated approximately 10% lower PF-MDA8 O3 concentrations and, consequently, approximately 10% fewer PF-MDA8 O3-attributable premature deaths than the 12-km simulation. These findings highlight the regional health relevance of PF-related O3 and underscore the need to integrate air-quality and public-health considerations into future PF management, particularly under climate-driven increases in fire activity.