Impact of Prescribed Fire Emissions on Ambient PM2.5 and Its Components in the Southeastern US

Abstract

Under the framework of the United Nations Sustainable Development Goals, mitigating global PM_2.5 exposure, which poses a substantial health threat, has become a critical global priority. However, in the southeastern United States (US), the increased use of prescribed fire (PF) or controlled burning as a predominant management tool to prevent destructive wildfires is a major source of PM_2.5. Despite widespread smoke exposure in this region, the concentrations of PF-induced PM_2.5 (PF–PM_2.5), its chemical composition, and its seasonal variability remain poorly understood. Moreover, it is important to quantify the contribution of PF to black carbon in the atmosphere to assess the climatic impact of these burns. We employed a multistage modeling framework to estimate year-round, long-term effects of PF on air quality. The framework integrates a chemical transport model with a data-fusion approach to estimate 24 h average PF–PM_2.5 and its components [elemental carbon (EC), organic carbon (OC), nitrate (NO^–₃), sulfate (SO^2–₄), and others] attributable to PF from 2013 to 2021 in 12 southeastern US. We estimated average PF–PM_2.5 to be 0.50 ± 0.20 μg/m³ (mean ± SD), which was approximately 8% of the ambient PM_2.5. The hot spots with a high PF–PM_2.5 concentration appeared over southeast Alabama, southwest Georgia, and northwestern Florida. From 2013–2021, average PF–PM_2.5 contributed 0.85 ± 0.17 μg/m³ (12% of ambient PM_2.5) in Georgia and 0.83 ± 0.16 μg/m³ (11% of ambient PM_2.5) in Alabama. However, during the extensive burning season (January–April), average PF–PM_2.5 levels accounted for 1.38 ± 0.31 μg/m³ (20% of ambient PM_2.5) in Georgia and 1.11 ± 0.27 μg/m³ (16% of ambient PM_2.5) in Alabama. The 2013–2021 average PF-EC value was 0.067 ± 0.028 μg/m³ over the 12 states, which was 27% of ambient EC and increased to 35% of ambient EC during the extensive burning season (0.091 ± 0.045 μg/m³). The average PF-OC concentration was also high, 0.23 ± 0.09 μg/m³ (13% of ambient OC); however, average concentrations of PF-NO^-₃, PF-SO^2-₄, and other components were very low during the study period. The PF–PM_2.5 and its components’ concentrations were highly dependent on place and season. This data set can be used as a tool to aid in understanding the interplay between forest management, air quality, and human health in the southeastern US.