Field measurements of trace gases emitted by prescribed fires in southeastern US pine forests using an open-path FTIR system

摘要

We report trace-gas emission factors from three pine-understory prescribedfires in South Carolina, US measured during the fall of 2011. The fireswere more intense than many prescribed burns because the fuels includedmature pine stands not subjected to prescribed fire in decades that were litfollowing an extended drought. Emission factors were measured with a fixedopen-path Fourier transform infrared (OP-FTIR) system that was deployed onthe fire control lines. We compare these emission factors to those measuredwith a roving, point sampling, land-based FTIR and an airborne FTIR deployedon the same fires. We also compare to emission factors measured by a similarOP-FTIR system deployed on savanna fires in Africa. The data suggest thatthe method used to sample smoke can strongly influence the relativeabundance of the emissions that are observed. The majority of fire emissionswere lofted in the convection column and were sampled by the airborne FTIR.The roving, ground-based, point sampling FTIR measured the contribution ofindividual residual smoldering combustion fuel elements scattered throughoutthe burn site. The OP-FTIR provided a ~ 30 m path-integratedsample of emissions transported to the fixed path via complex ground-levelcirculation. The OP-FTIR typically probed two distinct combustion regimes,"flaming-like" (immediately after adjacent ignition and before theadjacent plume achieved significant vertical development) and"smoldering-like." These two regimes are denoted "early" and "late",respectively. The path-integratedsample of the ground-level smoke layer adjacent to the fire from the OP-FTIRprovided our best estimate of fire-line exposure to smoke for wildland firepersonnel. We provide a table of estimated fire-line exposures for numerousknown air toxics based on synthesizing results from several studies. Ourdata suggest that peak exposures are more likely to challenge permissibleexposure limits for wildland fire personnel than shift-average (8 h)exposures.