The Effect of Combustion Conditions on Emissions of Elemental Carbon and Organic Carbon and Formation of Secondary Organic Carbon in Simulated Wildland Fires ACS ES&T Air

We investigated the influence of combustion conditions on emissions of elemental carbon (EC) and organic carbon (OC) and the formation of secondary organic carbon (SOC) in wildland fires. We performed combustion experiments using fuel beds representative of three ecoregions in the Southeastern U.S. and varied the fuel-bed moisture content to simulate either prescribed fires (Rx) or drought-induced wildfires (Wild). We used fire radiative energy normalized by fuel-bed mass (FREnorm) as a proxy for combustion conditions. For fuel beds that contained surface fuels only, the higher moisture content in Rx led to lower FREnorm compared to Wild and consequently led to lower EC emissions, but higher OC emissions and SOC formation. For fuel beds that contained duff in addition to surface fuels, duff did not ignite in Rx because of the high moisture content. However, duff ignited in Wild, leading to prolonged smoldering and substantially lower FREnorm in Wild compared to Rx. Consequently, OC emissions and SOC formation were an order of magnitude higher in Wild compared to Rx for the duff-containing fuel beds. These findings indicate that characterizing fuel availability and variability in combustion conditions, which emerges from variability in fuel-bed composition and environmental conditions, is crucial for determining carbonaceous aerosol formation in wildland fires. Grant no. NA22SEC4810015 Grant no. NA22SEC4810015