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Abstract
Abstract. Forest fires are major contributors of reactive gas- and particle-phase organic compounds to the atmosphere. We used offline high-resolution tandem mass spectrometry to perform a molecular-level speciation of gas- and particle-phase compounds sampled via aircraft from an evolving boreal forest fire smoke plume in Saskatchewan, Canada. We observed diverse multifunctional compounds containing oxygen, nitrogen, and sulfur (CHONS), whose structures, formation, and impacts are understudied. The dilution-corrected absolute ion abundance of particle-phase CHONS compounds increased with plume age by a factor of 6.4 over the first 4 h of downwind transport, and their relative contribution to the observed functionalized organic aerosol (OA) mixture increased from 19 % to 40 %. The dilution-corrected absolute ion abundance of particle-phase compounds with sulfide functional groups increased by a factor of 13 with plume age, and their relative contribution to observed OA increased from 4 % to 40 %. Sulfides were present in up to 75 % of CHONS compounds and the increases in sulfides were accompanied by increases in ring-bound nitrogen; both increased together with CHONS prevalence. A complex mixture of intermediate- and semi-volatile gas-phase organic sulfur species was observed in emissions from the fire and depleted downwind, representing potential precursors to particle-phase CHONS compounds. These results demonstrate CHONS formation from nitrogen- and oxygen-containing biomass burning emissions in the presence of reduced sulfur species. In addition, they highlight chemical pathways that may also be relevant in situations with elevated emissions of nitrogen- and sulfur-containing organic compounds from residential biomass burning and fossil fuel use (e.g., coal), respectively.
Highlights
Forest fires are predicted to become increasingly prevalent and severe with climate change (Abatzoglou and Williams, 2016; Barbero et al, 2015; Jolly et al, 2015)
Our analysis of functionalized organic aerosol (OA) showed several compositional trends in the evolving boreal forest fire smoke plume and exhibited marked changes after emissions from the oil sands facilities were mixed with the forest fire plume
There was a continual decrease in the relative abundance of particle-phase CHO compounds in the observed functionalized OA across screens 1–4, accompanied by a consistent relative increase in CHON and CHONS compounds (Fig. 1b)
Summary
Forest fires are predicted to become increasingly prevalent and severe with climate change (Abatzoglou and Williams, 2016; Barbero et al, 2015; Jolly et al, 2015) These fires are an important and uncontrolled source of gas- and particlephase compounds to the atmosphere, including a complex mixture of gas-phase reactive organic carbon, primary organic aerosol (POA), carbon monoxide, carbon dioxide, methane, ammonia, nitrogen oxides, and black carbon (Akagi et al, 2011; Gilman et al, 2015; Hatch et al, 2015, 2018; Koss et al, 2018; Vicente et al, 2013; Yokelson et al, 2013). Ditto et al.: Evolution of emissions from a boreal forest fire
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