Boreal forest fire emissions in fresh Canadian smoke plumes: Csub1/sub-Csub10/sub volatile organic compounds (VOCs), COsub2/sub, CO, NOsub2/sub, NO, HCN and CHsub3/subCN

摘要

Boreal regions comprise about 17 % of the global land area, and they bothaffect and are influenced by climate change. To better understand borealforest fire emissions and plume evolution, 947 whole air samples werecollected aboard the NASA DC-8 research aircraft in summer 2008 as part ofthe ARCTAS-B field mission, and analyzed for 79 non-methane volatile organiccompounds (NMVOCs) using gas chromatography. Together with simultaneousmeasurements of CO₂, CO, CH₄, CH₂O, NO₂, NO, HCN andCH₃CN, these measurements represent the most comprehensive assessmentof trace gas emissions from boreal forest fires to date. Based on 105 airsamples collected in fresh Canadian smoke plumes, 57 of the 80 measuredNMVOCs (including CH₂O) were emitted from the fires, including 45species that were quantified from boreal forest fires for the first time.After CO₂, CO and CH₄, the largest emission factors (EFs) forindividual species were formaldehyde (2.1 ± 0.2 g kg?1), followedby methanol, NO₂, HCN, ethene, α-pinene, β-pinene, ethane, benzene,propene, acetone and CH₃CN. Globally, we estimate that boreal forestfires release 2.4 ± 0.6 Tg C yr?1 in the form of NMVOCs, withapproximately 41 % of the carbon released as C₁-C₂ NMVOCs and21 % as pinenes. These are the first reported field measurements ofmonoterpene emissions from boreal forest fires, and we speculate that thepinenes, which are relatively heavy molecules, were detected in the fireplumes as the result of distillation of stored terpenes as the vegetation isheated. Their inclusion in smoke chemistry models is expected to improvemodel predictions of secondary organic aerosol (SOA) formation. Thefire-averaged EF of dichloromethane or CH₂Cl₂, (6.9 ± 8.6) × 10?4 g kg?1, was not significantly different from zeroand supports recent findings that its global biomass burning source appearsto have been overestimated. Similarly, we found no evidence for emissions ofchloroform (CHCl₃) or methyl chloroform (CH₃CCl₃) from borealforest fires. The speciated hydrocarbon measurements presented here show theimportance of carbon released by short-chain NMVOCs, the strong contributionof pinene emissions from boreal forest fires, and the wide range of compoundclasses in the most abundantly emitted NMVOCs, all of which can be used toimprove biomass burning inventories in local/global models and reduceuncertainties in model estimates of trace gas emissions and their impact onthe atmosphere.