Greenhouse gas emissions from laboratory-scale fires in wildland fuels depend on fire spread mode and phase of combustion

N C Surawski,C P Meyer,S H Roxburgh,A L Sullivan,P J Polglase

doi:10.5194/acp-15-5259-2015

N C Surawski, C P Meyer + Show 3 more

Open Access

https://doi.org/10.5194/acp-15-5259-2015

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Abstract

Abstract. Free-burning experimental fires were conducted in a wind tunnel to explore the role of ignition type and thus fire spread mode on the resulting emissions profile from combustion of fine (< 6 mm in diameter) Eucalyptus litter fuels. Fires were burnt spreading with the wind (heading fire), perpendicular to the wind (flanking fire) and against the wind (backing fire). Greenhouse gas compounds (i.e. CO2, CH4 and N2O) and CO were quantified using off-axis integrated-cavity-output spectroscopy. Emissions factors calculated using a carbon mass balance technique (along with statistical testing) showed that most of the carbon was emitted as CO2, with heading fires emitting 17% more CO2 than flanking and 9.5% more CO2 than backing fires, and about twice as much CO as flanking and backing fires. Heading fires had less than half as much carbon remaining in combustion residues. Statistically significant differences in CH4 and N2O emissions factors were not found with respect to fire spread mode. Emissions factors calculated per unit of dry fuel consumed showed that combustion phase (i.e. flaming or smouldering) had a statistically significant impact, with CO and N2O emissions increasing during smouldering combustion and CO2 emissions decreasing. Findings on the equivalence of different emissions factor reporting methods are discussed along with the impact of our results for emissions accounting and potential sampling biases associated with our work. The primary implication of this study is that prescribed fire practices could be modified to mitigate greenhouse gas emissions from forests by judicial use of ignition methods to induce flanking and backing fires over heading fires.

Highlights

Wildfires emit a variety of pollutants to the atmosphere which have impacts on global warming, biogeochemical cycles, ambient air quality and human health (Mack et al, 2011; Monks et al, 2009; Weinhold, 2011)
This study has explored the hypothesis that fire spread mode and phase of combustion can lead to differences in emissions factors of greenhouse gases from laboratory-scale fires conducted in a wind tunnel facility
We found that both fire spread mode and combustion phase had statistically significant impacts on emissions of greenhouse gases

Summary

Introduction

Wildfires emit a variety of pollutants to the atmosphere which have impacts on global warming, biogeochemical cycles, ambient air quality and human health (Mack et al, 2011; Monks et al, 2009; Weinhold, 2011). Wildfires contribute approximately 23 % of total anthropogenic greenhouse gas equivalent emissions (Houghton et al, 2009; van der Werf et al, 2010) there can be significant year-to-year variability. The main greenhouse gas species of interest emitted by wildfire include CO2, CH4 and N2O. Wildfires emit particulate matter (PM) to the atmosphere that has an impact on climate due to its ability to absorb and scatter light (Reid et al, 2005). The effect of wildfire PM on the aerosol indirect effect (i.e. cloud formation) remains poorly quantified at present (Bowman et al, 2009)

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