Ground Based Studies to Evaluate the Impacts of Prescribed Burning on Production of Secondary Species

RIME EL ASMAR, Rodney J. Weber, Greg Huey, M. Talat Odman, David Tanner, Georgia Institute of Technology

     Abstract Number: 287
     Working Group: Combustion

Abstract
The use of prescribed burning in managing ecosystems and preventing wildfires has been increasing in the US. Prescribed burning is conducted in favorable weather and fuel conditions to ensure maintaining control of the fire. These fires may negatively affect the local and regional air quality due to emissions of particulate matter (PM) and gaseous compounds and formation of secondary pollutants. In this work, ground-based measurements of smoke from prescribed fires in southeastern US were taken during the burning seasons of 2021, 2022, and 2023 at different US military Forts that perform regular prescribed burns. Emissions of trace gases (CO, O₃, and NO_x) and particles (PM_2.5 mass, BC, and BrC) and evolution of these species were studied. Ozone levels followed typical diurnal patterns with higher concentrations of 45-50 ppb during a typical afternoon in fair weather conditions. During these periods, additional ozone enhancements (∆O₃) were always observed in smoke impacted airmasses (range ∆O₃: 6.3-95.8 ppb), and ∆O₃/∆CO was found to be high in smoke of higher estimated ages for up to 6 hours, with a strong correlation of ∆O3/∆CO with physical age of smoke (r2=0.89). In all these cases, ∆PM_2.5/∆CO increase with physical age was also observed; there was a strong correlation between ∆PM_2.5/∆CO and age (r2=0.65). In contrast, no clear trend in ∆PM_2.5/∆CO with physical age was observed for smoke without ozone enhancements including plumes measured at night. This suggests that photochemically-driven secondary aerosol formation consistently occurred only in the plumes detected in the afternoon. The aim of this study is to investigate prescribed fire emissions and smoke evolution for evaluating models used in wildland fire management, to help sustain burning while minimizing adverse effects on air quality.