10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Optical Properties of Biomass Burning Carbonaceous Aerosol from Controlled Laboratory Burns and Ambient Wildfires
DIAN ROMONOSKY, Samantha Gomez, Jared Lam, Christian Carrico, Allison Aiken, Petr Chylek, Thom Rahn, Manvendra Dubey, Los Alamos National Lab
Abstract Number: 1403 Working Group: Carbonaceous Aerosol
Abstract Biomass burning and wildfires are important regional sources of particles and trace gases that degrade air quality, visibility, and impact climate. Light absorbing carbonaceous aerosol (LACA) and light scattering carbonaceous aerosol (LSCA) are major components of these optically complex emissions. The most absorbing class of LACA is refractory-LACA (r-LACA), commonly referred to as soot. Another component of LACA includes brown carbon (BrC), which is formed in the atmosphere, is non-refractory (nr-LACA), and has steeper absorption at shorter wavelengths than r-LACA. Both r-LACA and nr-LACA from biomass burning sources contribute to atmospheric warming. However, different processes control the amount of r-LACA and nr-LACA that are emitted and their evolution in the atmosphere, which determines the aerosol properties. These processes include fuel composition and combustion phase in the near field as well as the water affinity, volatility and photochemical processes in the far field. To better understand the optical properties of biomass burning aerosol, laboratory studies of smoke emissions were conducted in the Center for Aerosol Experiments (CAFÉ), at Los Alamos National Laboratory. The focus was on both native and invasive species found in the Southwestern U.S. to examine the influence fuel type and combustion conditions had on biomass burning emissions. During this time, ambient events were also measured at CAFÉ, including the El Cajete/Bonita wildfire (June 2017) and the Jemez/Valles Caldera prescribed burns (October 2017). Here we report and analyze single scattering albedo (SSA), absorption angstrom exponent (AAE), and mass absorption coefficient (MAC) values from the laboratory burns and wildfire events. Preliminary results show our laboratory burns produced aerosol with a wide range of optical properties, with some producing more strongly light-absorbing particles (SSA at 405 nm = 0.4-0.5) and others producing weakly light absorbing particles (SSA at 405 nm ≈1). AAE (405/780 nm) ranged from 1, indicative of r-LACA, to 4.5, suggesting the presence of nr-LACA during flaming and smoldering combustion phases. MACs for r-LACA show variability attributed to mixing state changes. The variability in our laboratory burns was found to be greater than in ambient fires, indicating a confluence of optical properties for ambient aged aerosol in comparison to the near-field laboratory emissions. We will present direct measurements of MACs of organic aerosol (including LACA and LSCA) using our SP-AMS. Mie theory calculations constrained by observed size distributions are used to interpret the optical properties of the smoke. Our results will gain insights into fundamental processes controlling the optical properties of biomass burning smoke and explain its variability to better predict their impact on climate.