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Abstract. Western US wildlands experience frequent and large-scale wildfires which arepredicted to increase in the future. As a result, wildfire smoke emissionsare expected to play an increasing role in atmospheric chemistry whilenegatively impacting regional air quality and human health. Understanding theimpacts of smoke on the environment is informed by identifying andquantifying the chemical compounds that are emitted during wildfires and byproviding empirical relationships that describe how the amount andcomposition of the emissions change based upon different fire conditions andfuels. This study examined particulate organic compounds emitted from burningcommon western US wildland fuels at the US Forest Service Fire ScienceLaboratory. Thousands of intermediate and semi-volatile organic compounds(I/SVOCs) were separated and quantified into fire-integrated emission factors(EFs) using a thermal desorption, two-dimensional gas chromatograph withonline derivatization coupled to an electron ionization/vacuum ultraviolethigh-resolution time-of-flight mass spectrometer(TD-GC × GC-EI/VUV-HRToFMS). Mass spectra, EFs as a function ofmodified combustion efficiency (MCE), fuel source, and other definingcharacteristics for the separated compounds are provided in the accompanyingmass spectral library. Results show that EFs for total organic carbon (OC),chemical families of I/SVOCs, and most individual I/SVOCs span 2–5 orders ofmagnitude, with higher EFs at smoldering conditions (low MCE) than flaming.Logarithmic fits applied to the observations showed that log (EFs) forparticulate organic compounds were inversely proportional to MCE. Thesemeasurements and relationships provide useful estimates of EFs for OC,elemental carbon (EC), organic chemical families, and individual I/SVOCs as afunction of fire conditions.
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Reconciling the total carbon budget for boreal forest wildfire emissions using airborne observations
Wildfire impacts on air quality and climate are expected to be exacerbatedby climate change with the most pronounced impacts in the boreal biome.Despite the large geographic coverage, there is limited information onboreal forest wildfire emissions, particularly for organic compounds, whichare critical inputs for air quality model predictions of downwind impacts.In this study, airborne measurements of 193 compounds from 15 instruments,including 173 non-methane organics compounds (NMOG), were used to providethe most detailed characterization, to date, of boreal forest wildfireemissions. Highly speciated measurements showed a large diversity ofchemical classes highlighting the complexity of emissions. Usingmeasurements of the total NMOG carbon (NMOGT), the ΣNMOG wasfound to be 50 % ± 3 % to 53 % ± 3 % of NMOGT, of which, theintermediate- and semi-volatile organic compounds (I/SVOCs) were estimatedto account for 7 % to 10 %. These estimates of I/SVOC emission factorsexpand the volatility range of NMOG typically reported. Despite extensivespeciation, a substantial portion of NMOGT remained unidentified(47 % ± 15 % to 50 % ± 15 %), with expected contributions from morehighly-functionalized VOCs and I/SVOCs. The emission factors derived in thisstudy improve wildfire chemical speciation profiles and are especiallyrelevant for air quality modelling of boreal forest wildfires. Theseaircraft-derived emission estimates were further linked with those derivedfrom satellite observations demonstrating their combined value in assessingvariability in modelled emissions. These results contribute to theverification and improvement of models that are essential for reliablepredictions of near-source and downwind pollution resulting from borealforest wildfires.
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- Award ID(s):
- 1764126
- PAR ID:
- 10493757
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Copernicus
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 22
- Issue:
- 18
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 12493 to 12523
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-22-12493-2022
