Abstract
Abstract. We have measured emission factors for 19 trace gas species and particulate matter (PM2.5) from 14 prescribed fires in chaparral and oak savanna in the southwestern US, as well as conifer forest understory in the southeastern US and Sierra Nevada mountains of California. These are likely the most extensive emission factor field measurements for temperate biomass burning to date and the only published emission factors for temperate oak savanna fuels. This study helps to close the gap in emissions data available for temperate zone fires relative to tropical biomass burning. We present the first field measurements of the biomass burning emissions of glycolaldehyde, a possible precursor for aqueous phase secondary organic aerosol formation. We also measured the emissions of phenol, another aqueous phase secondary organic aerosol precursor. Our data confirm previous observations that urban deposition can impact the NOx emission factors and thus subsequent plume chemistry. For two fires, we measured both the emissions in the convective smoke plume from our airborne platform and the unlofted residual smoldering combustion emissions with our ground-based platform. The smoke from residual smoldering combustion was characterized by emission factors for hydrocarbon and oxygenated organic species that were up to ten times higher than in the lofted plume, including high 1,3-butadiene and isoprene concentrations which were not observed in the lofted plume. This should be considered in modeling the air quality impacts for smoke that disperses at ground level. We also show that the often ignored unlofted emissions can significantly impact estimates of total emissions. Preliminary evidence suggests large emissions of monoterpenes in the residual smoldering smoke. These data should lead to an improved capacity to model the impacts of biomass burning in similar temperate ecosystems.
Highlights
Biomass burning is the largest source of primary, fine carbonaceous particles and a significant source of trace gases in the global atmosphere (Bond et al, 2004; Crutzen and Andreae, 1990) and impacts both the chemical composition as well as the radiative balance of the atmosphere
Area Burned noa nob nob nob yes no yesc noc nob nob nob yes yes yes a Fire was ignited after the daytime Terra and Aqua overpasses. b Fire was obscured by clouds during the daytime Terra and Aqua overpasses. c Fire was obscured by clouds during the daytime Terra and Aqua overpasses; the Turtle Fire was detected by the nighttime Terra overpass
Since the majority of the carbon mass (>98– 99 %) is represented by the compounds CO2, CO, and CH4; considering only the carbon-containing compounds that are detected by the FTIR in the mass balance approach only inflates the emission factors by ∼1–2 % (Yokelson et al, 2007b)
Summary
Biomass burning is the largest source of primary, fine carbonaceous particles and a significant source of trace gases in the global atmosphere (Bond et al, 2004; Crutzen and Andreae, 1990) and impacts both the chemical composition as well as the radiative balance of the atmosphere. The low MODIS detection rate for small fires is not critical in the western US where large wildfires dominate annual burned area; it poses a significant impediment to the development of fire emission inventories in the southeast where small, prescribed fires (average size = 60 ha) comprise ∼60 % of annual burned area for 2001–2010 (NIFC, 2011). The contribution of these US temperate burning emissions is relatively small on the global scale (van der Werf et al, 2010). Wilmington, NC Fresno, CA Fresno, CA Vandenberg AFB, CA Vandenberg AFB, CA Vandenberg AFB, CA Buellton, CA Ventura, CA Sierra Vista, AZ
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