Photochemical Evolution of the 2013 California Rim Fire: Synergistic Impacts of Reactive Hydrocarbons and Enhanced Oxidants
- 1Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
- 2Department of Oceanic and Atmospheric Science, University of Maryland, College Park, MD, USA
- 3Department of Chemistry, University of California Irvine, Irvine, CA, USA
- 4Institute for Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
- 5Department of Chemistry, University of Oslo, Oslo, Norway
- 6Chemical Sciences Laboratory, NOAA, Boulder, CO, USA
- 7Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA
- 8Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
- 9Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, USA
- 10School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- 11Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA
- 12Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
- 13Department of Chemistry, University of Colorado Boulder, Boulder, CO, USA
- 14Atmsopheric Sciences Branch, NASA Ames Research Center, Moffett Field, CA, USA
- 15NASA Langley Research Center, Hampton, VA, USA
- 16National Institute of Aerospace, Hampton, VA, USA
- 17Department of Earth and Planetary Sciences, University of California, Berkeley, CA, USA
- 18College of Chemistry, University of California, Berkeley, CA, USA
- anow at: Scientific Aviation, Boulder, CO, USA
- bnow at: Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA
- cnow at: Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, MD, USA
- dnow at: Fifty Years, San Francisco, CA, USA
- enow at: California Air Resource Board, Los Angeles, CA, USA
Abstract. Large wildfires markedly alter regional atmospheric composition, but chemical complexity challenges model predictions of downwind impacts. Here, we elucidate key facets of gas-phase photochemistry and assess novel chemical processes via a case study of the 2013 California Rim Fire plume. Airborne in situ observations, acquired during the NASA Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) mission, illustrate the evolution of volatile organic compounds (VOC), oxidants, and reactive nitrogen over 12 hours of atmospheric aging. Measurements show rapid formation of ozone and peroxyacyl nitrates (PNs), sustained peroxide production, and prolonged enhancements in oxygenated VOC and nitrogen oxides (NOx).
Measurements and Lagrangian trajectories constrain a 0-D puff model that approximates plume photochemical history and provides a framework for evaluating key processes. Simulations examine the effects of 1) previously-unmeasured reactive VOC identified in recent laboratory studies, and 2) emissions and secondary production of nitrous acid (HONO). Inclusion of estimated unmeasured VOC leads to a 250 % increase in OH reactivity and a 70 % increase in radical production via oxygenated VOC photolysis. HONO amplifies radical cycling and serves as a downwind NOx source, although two different HONO production mechanisms (particulate nitrate photolysis and heterogeneous NO2 conversion) exhibit markedly different effects on ozone, NOx, and PNs. Analysis of radical initiation rates suggests that oxygenated VOC photolysis is a major radical source, exceeding HONO photolysis when averaged over the first 2 hours of aging. Ozone production chemistry transitions from VOC-sensitive to NOx-sensitive within the first hour of plume aging, with both peroxide and organic nitrate formation contributing significantly to radical termination. To simulate smoke plume chemistry accurately, models should simultaneously account for the full reactive VOC pool and all relevant oxidant sources.
Glenn M. Wolfe et al.
Glenn M. Wolfe et al.
SEAC4RS observations https://www-air.larc.nasa.gov/cgi-bin/ArcView/seac4rs
Model code and software
F0AM Box Model https://github.com/AirChem/F0AM/releases/tag/v4.2.1
Glenn M. Wolfe et al.
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