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Preprints
https://doi.org/10.5194/acp-2020-239
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-239
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  20 Apr 2020

20 Apr 2020

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A revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Rapid Evolution of Aerosol Particles and their Optical Properties Downwind of Wildfires in the Western U.S.

Lawrence I. Kleinman1, Arthur J. Sedlacek III1, Kouji Adachi2, Peter R. Buseck3, Sonya Collier4,a, Manvendra K. Dubey5, Anna L. Hodshire6, Ernie Lewis1, Timothy B. Onasch7, Jeffery R. Pierce6, John Shilling8, Stephen R. Springston1, Jian Wang1,b, Qi Zhang4,b, Shan Zhou4,c, and Robert J. Yokelson9 Lawrence I. Kleinman et al.
  • 1Environmental and Climate Sciences Department, Brookhaven National Laboratory, Upton, NY, USA
  • 2Atmospheric Environment and Applied Meteorology Research Department, Meteorological Research Institute, Tsukuba, Japan
  • 3School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
  • 4Department of Environmental Toxicology, University of California, Davis, CA, USA
  • 5Earth Systems Observations, Los Alamos National Laboratory, Los Alamos, NM, USA
  • 6Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA
  • 7Aerodyne Research Inc., Billerica, MA, USA
  • 8Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA
  • 9Department of Chemistry and Biochemistry, University of Montana, Missoula, MT 59812
  • anow at: California Air Resources Board
  • bnow at: Center for Aerosol Science and Engineering, Washington University, St. Louis, MO
  • cnow at: Department of Chemistry, Syracuse University, Syracuse, NY

Abstract. During the first phase of the Biomass Burn Operational Project (BBOP) field campaign, conducted in the Pacific Northwest, the DOE G-1 aircraft was used to follow the time evolution of wildfire smoke from near the point of emission to locations 2–3.5 hours downwind. In nine flights we made repeated transects of wildfire plumes at varying downwind distances and could thereby follow the plume's time evolution. On average there was little change in dilution-normalized aerosol mass concentration as a function of downwind distance. This consistency hides a dynamic system in which primary aerosol particles are evaporating and secondary ones condensing. Organic aerosol is oxidized as a result. On all transect more than 90 % of aerosol is organic. In freshly emitted smoke aerosol, NH4+ is approximately equivalent to NO3. After two hours of daytime aging, NH4+ increased and is approximately equivalent to the sum of Cl, SO42− and NO3. Particle size increased with downwind distance causing particles to be more efficient scatters. Averaged over nine flights, mass scattering efficiency increased in ~ two hours by 56 % and in one fight doubled. Coagulation and material transport from small to large particles are discussed as mechanisms for increasing particle size. As absorption remained nearly constant with age the time evolution of single scatter albedo was controlled by age-dependent scattering. Near-fire aerosol had a single scatter albedo (SSA) of 0.8–0.9. After one to two hours of aging SSAs were typically 0.9 and greater. Assuming global-average surface and atmospheric conditions, the observed age-dependence in SSA would change the direct radiative effect of a wildfire plume from near zero near the fire to a cooling effect downwind.

Lawrence I. Kleinman et al.

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Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Lawrence I. Kleinman et al.

Lawrence I. Kleinman et al.

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Short summary
Aerosols from wildfires effect the Earth's temperature by absorbing light or reflecting it back into space. This study investigates time-dependent chemical, microphysical, and optical properties of aerosols generated by wildfires in the Pacific Northwest, USA. Wildfire smoke plumes were traversed by an instrumented aircraft at locations near the fire and up to 3.5-hour travel time downwind. Although there was no net aerosol production, aerosol particles grew and became more efficient scatters.
Aerosols from wildfires effect the Earth's temperature by absorbing light or reflecting it back...
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