10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Speciated Molecular Emission Factors and Volatilities of Biomass Burning Aerosols from Western US Forest Fuels
COTY JEN, Lindsay Hatch, Nathan Kreisberg, Christos Stamatis, Vanessa Selimovic, Robert J. Yokelson, Kelley Barsanti, Allen H. Goldstein, University of California, Berkeley
Abstract Number: 104 Working Group: Carbonaceous Aerosol
Abstract Wildfires are predicted to become larger and more frequent in many temperate and boreal forests, primarily due to changing climate (e.g. longer springs and summers, earlier snow melts, and prolonged droughts). Wildfires, and biomass burning more generally, are a dominant source of carbonaceous aerosols into the atmosphere, and represent a large fraction of gaseous volatile organic compound (VOC) emissions globally. It is predicted that > 50% of the non-methane organic chemicals from biomass burning are intermediate and/or semi volatile compounds (I/SVOCs) that can further react and partition into aerosol particles. The identities and quantities of most of I/SVOCs remain unknown, leading to uncertainty in predicting the extent to which wildfire smoke impacts air quality, human health, and the environment now and in the future.
This study examines the chemical identities and volatilities of molecules found in smoke produced from laboratory fires during the FIREX Fire Laboratory (US Forest Service, Missoula, MT) campaign and prescribed burning in the foothills of the Sierra Nevada (Blodgett Forest Research Station, CA). Filter and sorbent tube samples of fresh emissions were collected from the smoke stack at the Fire Lab for a variety of trees, ground cover, and shrubs typically found in the Western US, a region susceptible to large scale wildfires. These observations were then compared to real fire samples collected from prescribed burns conducted at Blodgett Forest Research Station. Smoke samples were collected using an unmanned aircraft system (UAS) that flew 25-50 m above the burns and a ground-base station. A two-dimensional gas chromatogram coupled to an electron impact or vacuum ultra violet light high-resolution time of flight mass spectrometer (GCxGC EI/VUV HRToFMS) was used to speciate and quantify the I/SVOCs in collected smoke samples from both campaigns. In addition, vapor pressures and log of the effective saturation concentrations (log C*) for all ~3000 observed compounds were estimated from their retention times based on fit to known standards. Results indicate that smoldering burns (low modified combustion efficiency, MCE) from rotten logs and duff fuels produced the highest emission factors and likely produce the vast majority of smoke during wildfire burns. Higher MCE values or more flaming conditions, produced lower emission factors for all observed compounds across all fuel types. In addition, we combined GCxGC measurements of sorbent tubes and filters to quantify amounts of each compound class across the volatility groups. These results can be used in the future to construct partitioning models and help predict aerosol chemistry.