Preprints
https://doi.org/10.5194/acp-2019-1067
https://doi.org/10.5194/acp-2019-1067

  04 Feb 2020

04 Feb 2020

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

Evidence for a larger contribution of smoldering combustion to boreal forest fire emissions from tower observations in Alaska

Elizabeth B. Wiggins1, Arlyn Andrews2, Colm Sweeney2, John B. Miller2, Charles E. Miller3, Sander Veraverbeke4, Roisin Commane5, Steve Wofsy6, John M. Henderson7, and James T. Randerson1 Elizabeth B. Wiggins et al.
  • 1Department of Earth System Science, University of California, Irvine, California, USA
  • 2National Oceanic and Atmospheric Administration, Boulder, Colorado, USA
  • 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
  • 4Vrije University Amsterdam, Netherlands
  • 5Department of Earth and Environmental Sciences, Columbia University, Palisades, New York, USA
  • 6School of Engineering and Applied Sciences, Harvard, Cambridge, Massachusetts, USA
  • 7Atmospheric and Environmental Research, Inc., Lexington, Massachusetts, USA

Abstract. With recent increases in burned area within boreal forests that have been linked to climate warming, there is a need to better understand the composition of emissions and their impact on atmospheric composition. Most previous studies have estimated boreal fire emission factors from daytime samples collected via aircraft near fire plumes or at the surface near actively burning fires. Here we quantified emission factors for CO and CH4 from a massive regional fire complex in interior Alaska during the summer of 2015 using continuous high-resolution trace gas observations from the CRV tower (Fox, AK). Averaged over the 2015 fire season, the CO/CO2 emission ratio was 0.138±0.048 and the CO emission factor was 145±50 g CO per kg of dry biomass consumed. The CO/CO2 emission ratio was about 35 % higher and more variable than most previous aircraft-based estimates for fresh wildfire emissions. The mean CH4/CO2 emission ratio was 0.010±0.003 and the CH4 emission factor was 6.05±2.09 g CH4 per kg of dry biomass consumed, with means similar to previous reports. CO and CH4 emission factors varied in synchrony, with higher CH4 emission factors observed during periods with lower modified combustion efficiency (MCE). By coupling a fire emissions inventory with an atmospheric model, we identified that at least 35 individual fires contributed to trace gas variations measured at the CRV tower, representing a significant increase in sampling compared to the number of boreal fires measured in all previous boreal forest fire work. The model also indicated that typical mean transit times between trace gas emission and tower measurement were 1–3 days, indicating that the time series sampled combustion across day and night burning phases. The high and variable CO emission factor estimates reported here provide evidence for a more prominent role of smoldering combustion, highlighting the importance of continuously sampling of fires across time-varying environmental conditions that are representative of typical burning conditions.

Elizabeth B. Wiggins et al.

 
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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Elizabeth B. Wiggins et al.

Elizabeth B. Wiggins et al.

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Short summary
We analyzed high resolution trace gas measurements collected from a tower in Alaska during a very active fire season to improve our understanding of trace gas emissions from boreal forest fires. Our results suggest previous studies may have underestimated emissions from smoldering combustion in boreal forest fires. These fires likely emit more CO, CH4, and organic carbon aerosol into the atmosphere than previously thought.
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