Measurements of emissions from agricultural fires and wildfires in the U.S.
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Biomass burning (BB) produces significant amounts of trace gases and aerosol, which play important roles in atmospheric chemistry and climate. This study presents detailed airborne measurements of emissions from 15 agricultural fires and 3 wildfires in the U.S. during the 2013 Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and the Biomass Burning Observation Project (BBOP). A detailed set of emission factors (EFs) for 25 trace gases and 6 components of submicron particulate matter (PM1) was reported for the agricultural fires located in the southeastern U.S. Observed EFs are generally consistent with previous measurements of crop residue burning, but the fires studied here emitted high amounts of oxygenated volatile organic compounds, sulfur dioxide, and fine particles. Filter-based measurements of aerosol light absorption implied that brown carbon was ubiquitous in the plumes. The rapid chemical evolution of the primary emissions in 7 out of 15 agricultural plumes was examined in detail for ~1.2 hr. A Lagrangian plume cross-section model was used to simulate the evolution of ozone, reactive nitrogen species, and organic aerosol (OA). For the western wildfires, we measured an extensive set of EFs for over 80 gases and 5 PM1 species. The wildfires emitted high amounts of PM1 (in which OA comprised most of the mass) with an average EF that is over two times of prescribed fire EFs. The EFs were used to estimate the annual regional emissions from agricultural fires and wildfires for CO, NOx, total non-methane organic compounds, and PM1. Our wildfire PM1 emission estimate (1530 ± 570 Gg yr-1) from 11 western states is over three times that of the 2011 National Emissions Inventory (NEI) PM2.5 estimate, mainly due to our high EF(PM1), and also higher than the PM2.5 emitted from all other sources in these states according to NEI. This supports the practice of prescribed burning that could reduce fine particle emissions.