Changes in Biomass Burning Aerosol Radiative Properties Due to Atmospheric Processing of Wildfire Plumes Over the Northwestern United States

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This study will provide new insights about the chemical and physical properties of wildfire smoke. Ground-based measurements using state-of-the-art optical instrumentation will provide data on the aerosol optical and physico-chemical properties from wildfires and prescribed burns in the northwestern United States as part of an interagency collaborative field campaign (FIREX-AQ) funded by NOAA and NASA. A better understanding of the properties of smoke aerosol will improve both air quality and climate models. During the summer in 2019, a dual-cell, multi-wavelength integrated photoacoustic-nephelometer spectrometer and a portable asymmetry parameter monitor will be deployed to Boise Idaho for 4 weeks to characterize and constrain aerosol spectral optical properties as a function of fire phase, wildland fuel type, and daytime and nighttime aging of smoke. Controlled heterogeneous oxidation experiments of organic aerosol will be performed during select smoldering phase episodes using a Potential Aerosol Mass (PAM) oxidation flow tube reactor, which creates a highly oxidizing environment that simulates atmospheric oxidation processes on timescales ranging from a day up to several weeks in a short period of a few minutes. Some of the research questions that will be investigated as part of this study include the following: (1) How do the aerosol optical properties, scattering and absorption cross-sections, single scattering albedo, Angstrom exponent, and asymmetry parameter evolve with varying oxidation states, size, hygroscopicity, wildland fuel type and fire phase? (2) How do the wavelength-dependent complex refractive indices of light absorbing organic aerosol change with different degrees of atmospheric processing? (3) What is the contribution of the water-soluble organic carbon to absorption by organic aerosol? (4) What are the enhancement factors for mass absorption and scattering cross-sections of black carbon upon various degrees of internal mixing with organic aerosol? (5) Could mechanistic insight and simpler parameterizations using the concept of scaling laws be obtained for integration in process-based models? And (6) Can generalized inferences be deduced regarding distinctive and differentiating properties of organic aerosol microphysical and optical properties from real-world versus laboratory burns?This project includes several outreach activities, such as summer teacher training workshops for middle and high school teachers on air pollution.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.