25 Apr 2022
25 Apr 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Emissions of Organic Compounds from Western US Wildfires and Their Near Fire Transformations

Yutong Liang1,, Christos Stamatis2,a,, Edward C. Fortner3, Rebecca A. Wernis4, Paul Van Rooy2, Francesca Majluf3, Tara I. Yacovitch3, Conner Daube3, Scott C. Herndon3, Nathan M. Kreisberg5, Kelley C. Barsanti2, and Allen H. Goldstein1,4 Yutong Liang et al.
  • 1Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA, 94720, USA
  • 2Department of Chemical and Environmental Engineering and College of Engineering – Center for Environmental Research and Technology (CE-CERT), University of California, Riverside, Riverside, CA, 92507, USA
  • 3Aerodyne Research, Inc., 45 Manning Road, Billerica, MA, 01821, USA
  • 4Department of Civil and Environmental Engineering, University of California, Berkeley, California 94720, USA
  • 5Aerosol Dynamics, Inc., Berkeley, CA 94710, USA
  • anow at: Charles E. Via Jr. Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA, 24061, USA
  • These authors contributed equally to this work.

Abstract. The size and frequency of wildfires in the western United States have been increasing and this trend is projected to continue, with increasing adverse consequences for human health. Gas- and particle-phase organic compounds are the main component of wildfire emissions. Some of the directly emitted compounds are hazardous air pollutants, while others can react with oxidants to form secondary air pollutants such as ozone and secondary organic aerosol (SOA). Further, compounds emitted in the particle phase can volatize during smoke transport and can then serve as precursors for SOA. The extent of pollutant formation from wildfire emissions is dependent in part on the speciation of organic compounds. The most detailed speciation of organic compounds has been achieved in laboratory studies, though recent field campaigns are leading to an increase in such measurements in the field. In this study, we identified and quantified hundreds of gas- and particle-phase organic compounds emitted from conifer-dominated wildfires in the western US, using two two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC ToFMS) instruments. Observed emission factors (EFs) and emission ratios are reported for four wildfires. As has been demonstrated previously, modified combustion efficiency (MCE) was a good predictor of particle phase EFs, except for elemental carbon. Higher emissions of diterpenoids, resin acids and monoterpenes were observed in the field relative to laboratory studies; likely due to distillation from unburned heated vegetation, which may be underrepresented in laboratory studies. These diterpenoids and resin acids accounted for up to 45 % of total quantified organic aerosol, higher than the contribution from sugar and sugar derivatives. The low volatility of resin acids makes them ideal markers for conifer fire smoke. The speciated measurements also show that evaporation of semi-volatile organic compounds took place in smoke plumes, which suggests that the evaporated primary organic aerosol can be precursors of SOAs in wildfire smoke plumes.

Yutong Liang et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-297', Anonymous Referee #1, 26 May 2022
  • RC2: 'Comment on acp-2022-297', Anonymous Referee #2, 03 Jun 2022
  • AC1: 'Comment on acp-2022-297', Yutong Liang, 29 Jun 2022

Yutong Liang et al.

Yutong Liang et al.


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Short summary
This article reports the measurements of organic compounds emitted from western US wildfires. We have identified and quantified 240 particle-phase compounds and 72 gas-phase compounds emitted in wildfire, and related the emissions with the modified combustion efficiency. Higher emissions of diterpenoids and monoterpenes were observed, likely due to distillation from unburned heated vegetation. Our results can benefit future source apportionment or modeling studies and exposure assessments.