AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Western US Wildfire Emissions of Ice Nucleating Particles
PAUL DEMOTT, Kevin Barry, Ezra Levin, Kathryn Moore, Thomas Hill, Cynthia Twohy, Darin Toohey, Amy P. Sullivan, Sonia Kreidenweis, Emily Fischer, Colorado State University
Abstract Number: 632 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract The sources, abundance and nature of emissions of ice nucleating particles (INPs) affect aerosol-cloud interactions, precipitation, and climate in ways that are not well characterized. Contribution of biomass burning INPs is particularly poorly resolved. Most previous sampling of INPs emitted during wildfires was conducted from surface sites. There is need to examine INP emissions directly in wildfire plumes, including subsequent interactions with clouds, as INP inputs may vary with fire size, fuel, combustion efficiency and age, and may include lofted soils, ash, and plant material [McCluskey et al., J. Geophys. Res. Atmos., 119, 10,458–10,470, 2014].
INP measurements using an online continuous flow diffusion chamber and bulk offline filter collections for immersion freezing measurements were made via an isokinetic inlet, and from smoke-affected cloud particle residues via a counterflow virtual impactor inlet on the NSF/NCAR C-130 as part of the Western Wildfire Experiment for Cloud Chemistry, Aerosol, Absorption and Nitrogen study. Based from Boise, ID in summer 2018, numerous plumes and diffuse smoke regions were sampled over the intermountain west and northwest United States. In agreement with previous surface-based studies, order of magnitude average enhancements in INPs were observed in wildfire plumes compared to background air, indicating highly selective production of INPs compared to greater enhancements of total particles. Production with aging was inferred in some cases.
INP compositions, determined by TEM/EDS and chemical treatments of bulk samples, were dominated by thermally stable organic carbon mixtures with sulfates and other inorganics. Mineral and mixed INPs were always found, although in the minority compared to organic types. INP mode size was below 500 nm in cases analyzed thus far. Future work will develop parameterizations for wildfire INP sources over the full mixed-phase cloud temperature range, and utilize these for numerical modeling studies.