Reconciling the total carbon budget for boreal forest wildfire emissions using airborne observations

Abstract

Abstract. Wildfire impacts on air quality and climate are expected to be exacerbated by climate change with the most pronounced impacts in the boreal biome. Despite the large geographic coverage, there is limited information on boreal forest wildfire emissions, particularly for organic compounds, which are 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 provide the most detailed characterization, to date, of boreal forest wildfire emissions. Highly speciated measurements showed a large diversity of chemical classes highlighting the complexity of emissions. Using measurements of the total NMOG carbon (NMOGT), the ΣNMOG was found to be 50 % ± 3 % to 53 % ± 3 % of NMOGT, of which, the intermediate- and semi-volatile organic compounds (I/SVOCs) were estimated to account for 7 % to 10 %. These estimates of I/SVOC emission factors expand the volatility range of NMOG typically reported. Despite extensive speciation, a substantial portion of NMOGT remained unidentified (47 % ± 15 % to 50 % ± 15 %), with expected contributions from more highly-functionalized VOCs and I/SVOCs. The emission factors derived in this study improve wildfire chemical speciation profiles and are especially relevant for air quality modelling of boreal forest wildfires. These aircraft-derived emission estimates were further linked with those derived from satellite observations demonstrating their combined value in assessing variability in modelled emissions. These results contribute to the verification and improvement of models that are essential for reliable predictions of near-source and downwind pollution resulting from boreal forest wildfires.

Contribution of Carbonyl Chromophores in Secondary Brown Carbon from Nighttime Oxidation of Unsaturated Heterocyclic Volatile Organic Compounds

“…Given that biomass burning releases a variety of N-containing heterocyclic VOC precursors, − the formation of N-containing carbonyl chromophores could be a potentially significant contributor to the light absorption of secondary BrC. Furthermore, as widely observed in field studies of wildfire emissions, ,,, N-containing carbonyl chromophores offer another pivot in addition to the nitroaromatic chromophores for a more in-depth understanding of secondary BrC formation, particularly the wavelength-dependent change of BrC light absorption as well as the diverse physicochemical processes. Although nitroaromatic chromophores may likely possess stronger absorptivity compared to carbonyl chromophores, the former are largely related to anthropogenic emissions of NO x , , whereas the latter may be generated by more divergent atmospheric oxidation pathways, such as OH-driven oxidation of VOCs .…”

Total organic carbon measurements reveal major gaps in petrochemical emissions reporting

“…TC concentrations (excluding methane) were measured in April to July 2018 across box-shaped ( n = 16) and downwind flights ( n = 14) (table S1) in the Athabasca oil sands region (Alberta, Canada) by using an aircraft deployment of paired carbon dioxide (CO 2 ) analyzers, one with a catalyst-outfitted inlet to convert all organic gases to CO 2 ( 18 ). Elevated TC concentrations [>0.2 parts per million by carbon (ppmC)] were observed across facility locations and types (six surface mining and six in situ) (examples are given in Fig.…”

“…3). For example, flights 25 and 26 initially focused on a forest fire ( 18 , 35 ) upwind of oil sands operations, with the fifth screen, which was downwind of all major surface mining facilities, showing a marked enhancement in SVOC abundances and mass spectra indicative of oil sands–derived emissions (Figs. 2C and 3, A and B, and fig.…”

The Global Forest Fire Emissions Prediction System version 1.0

“…Other regional studies may provide additional validation data through remote sensing, particularly on a regional or individual fire basis. For example, Nguyen and Wooster (2020) estimated biomass burning in Africa using geostationary fire radiative power (FRP) and aerosol optical depth (AOD); Hayden et al (2022) Future direction of the GFFEPS model includes integration with the GEM-MACH chemical transport model, and 690 running the model operationally to provide boundary data and input for the regional CFFEPS model. This would allow for the transcontinental transport of smoke emissions into the air-quality forecasts for Canada.…”