Characterization of trace gas emissions from controlled laboratory burning of Canadian boreal forest fuels

Afroz, Rowshon; Shen, Hongru; Isenor, Bradley H.; Moussa, Samar G.; Hanashiro Moraes, Amanda; Talebian, Shakiba; Liu-Kang, Carolyn; Wentzell, Jeremy J. B.; Olfert, Oscar; Leithead, Amy; Marshall, Ginny; Staebler, Ralf M.; Mihele, Cris; Chan, Arthur W. H.; Olfert, Jason; Liggio, John; Abbatt, Jonathan; Zhao, Ran; Wren, Sumi N.

doi:10.5194/egusphere-2026-2661

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https://doi.org/10.5194/egusphere-2026-2661

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21 May 2026

| 21 May 2026

Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Characterization of trace gas emissions from controlled laboratory burning of Canadian boreal forest fuels

Rowshon Afroz, Hongru Shen, Bradley H. Isenor, Samar G. Moussa, Amanda Hanashiro Moraes, Shakiba Talebian, Carolyn Liu-Kang, Jeremy J. B. Wentzell, Oscar Olfert, Amy Leithead, Ginny Marshall, Ralf M. Staebler, Cris Mihele, Arthur W. H. Chan, Jason Olfert, John Liggio, Jonathan Abbatt, Ran Zhao, and Sumi N. Wren

Abstract. Although boreal wildfires are a major global source of trace gases, their emissions remain poorly characterized. To address this gap, controlled burns of Canadian Boreal surface and ground fuels were conducted during the Biomass Burning Canada (BBCan) Campaign. Emission factors (EF) for 46 volatile organic compounds (VOC) were determined using iodide chemical ionization mass spectrometry (I-CIMS) and Vocus proton transfer reaction mass spectrometry (Vocus PTR-MS). Total non-methane organic compound (NMOC) emissions, which were measured separately, were found to account for 1–13 % of total emitted gas-phase carbon (i.e., CO₂, CO, CH₄, NMOC), with total quantified VOCs (ΣVOCs) accounting for 13–34 % of that fraction. The dominant compounds contributing to the measured ΣVOCs include oxygenates and organic reactive nitrogen (Nr) species. Boreal peat fuels, which are prone to residual smoldering combustion, produced significantly higher total NMOC, total Nr, and individual VOC emissions than the other fuels. In contrast, boreal mulch, which burned very efficiently, produced low emissions. Combustion efficiency was observed to have a strong impact on total and individual VOC emissions, but VOC emission profiles were also dependent on fuel type and moisture content. The findings indicate that the EFs currently used to speciate NMOC emission may not adequately capture emissions from smoldering boreal peat fires. Study results provide the first comprehensive VOC EF for fresh emissions for a range of Canadian boreal surface and ground fuels, which can be used to improve emission inventories and enhance predictions of wildfire smoke impacts on air quality, climate, and health.

Received: 08 May 2026 – Discussion started: 21 May 2026

Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.

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RC1:
'Comment on egusphere-2026-2661', Anonymous Referee #1, 03 Jul 2026 reply
In this manuscript, Afroz et al. fill the gap in the current understanding of Canadian wildfire boreal surface fuels and provide useful implications for evaluating current Canadian wildfire emission inventories, which underestimate the Canadian boreal peat EF. This manuscript also takes advantage of two Picarro measurements to quantify the total NMOC and provides promising insight by using fuel moisture to explain the variability in VOC emissions. However, several aspects require further clarification. In particular, the manuscript needs better justification for the duct-flow-based EF calculation method relative to the more commonly used carbon mass balance approach, and for missing low-molecular-weight VOCs and gas-particle partitioning. In addition, some comparisons between laboratory and aircraft-based measurements would benefit from a more cautious interpretation that accounts for differences in fuel type, combustion conditions, plume age, dilution, chemical processing, and sampling platform.
My major comments are below:
Many of the studies used for comparison (like Koss et al., 2018; Permar et al., 2021) use the carbon-mass balance method for calculating EF. The manuscript should clarify the advantages and limitations of this method relative to the carbon-mass balance method. Because this study directly relies on measured duct flow, it would also be useful to describe whether and how the hood/duct system was validated to ensure complete smoke capture.

The emission factor calculation equation is defined for mixing ratio (ppb); then it should be converted to 10^-9 mol/mol. The authors should check the equation.

For the 46 VOC EFs, it would be helpful to compare the full set of reported VOCs with previous VOCs’ full mass spectrum biomass-burning studies. This comparison would also help clarify the origin of the “missing VOC” percentage discussed for Figure 3(c) and Lines 345–350. Important low-molecular-weight compounds, such as methanol and formaldehyde, were not quantified in this study, although these species have been shown in previous laboratory and wildfire studies to contribute substantially to total VOC mass. The manuscript would benefit from a simple quantitative comparison or discussion of the expected contribution of these missing compounds to better place the reported VOC mass fraction in context.

For Figure S7(c). GR (dry) and MU (dry) correlation is poor (R² =0.31). Additional explanation would be helpful. And are there any factors that affect it? Even for GR (dry, 20% moisture) and MU (dry, 4% moisture), they are considered “Dry”. Absolute fuel moisture can be a factor impacting the EF of VOCs beyond the fuel itself. It is helpful to clarify it.

Regarding the “Mag-Mode" the manuscript described in the supplementary material, the manuscript should explain more clearly how this bias was corrected. Are there any high m/z species that are underestimated?

Lines 270–275, gas and aerosol partitioning can play an important role in BB emission (May et al., 2013; Pagonis et al., 2023). This topic needs to be included in the discussion.

Detailed comments are:
Line 319, acrylic acid should be C₃H₄O₂.
Line 330-334, guaiacol is considered a low-temperature pyrolysis indicator in a PMF analysis. Even high- or low-temperature pyrolysis does not correspond exactly to the commonly used “flaming” or “smoldering”, but it still can be helpful to add here.
Line 372, can you explain why MU has poor correlations?
Line 391, most of the quantified VOC. How many? Can you present XX out of 46 or as a percentage?
Line 560, the higher EFs of HONO, NO, VOCs, and other species observed in lab studies compared with aircraft measurements cannot be explained simply by the difference between fresh and aged smoke. Other factors, such as differences in fuel type, peat contribution, fuel nitrogen content, combustion conditions, and sampling platform, can also affect this. For example, peat fuels can emit more N-containing species, while aircraft measurements of aged plumes may be affected by chemical processing, gas-particle partitioning, dilution, and possible loss or evaporation of SVOCs, IVOCs, etc.
Citation:
https://pubs.acs.org/doi/abs/10.1021/acs.est.3c05017
www.atmos-chem-phys.net/14/199/2014/
10.5194/acp-11-12197-2011
https://doi.org/10.1002/jgrd.50828

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Citation: https://doi.org/10.5194/egusphere-2026-2661-RC1

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https://doi.org/10.5194/egusphere-2026-2661-supplement

Data sets

Replication data for: Emission factors for gaseous species measured at the individual burn level using I-CIMS and Vocus PTR-MS Rowshon Afroz https://doi.org/10.5683/SP3/OGR3J1

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Short summary

Wildfires represent a dominant source of gaseous pollutants that affect air quality, climate, and health, but emissions from Canadian boreal fuels are not well characterized. We conducted controlled laboratory burns of representative fuels and measured gas emissions in detail. Emissions varied strongly with fuel type, moisture, and burning conditions, with peat producing especially high levels. These results improve emission estimates and help predict wildfire smoke impacts.


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