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https://doi.org/10.5194/acp-2020-1119
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-1119
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  06 Nov 2020

06 Nov 2020

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This preprint is currently under review for the journal ACP.

Where there is smoke there is mercury: Assessing boreal forest fire mercury emissions using aircraft and highlighting uncertainties associated with upscaling emissions estimates

David S. McLagan1,2, Geoff W. Stupple1, Andrea Darlington1, Katherine Hayden1, and Alexandra Steffen1 David S. McLagan et al.
  • 1Air Quality Research Division (ARQD), Environment and Climate Change Canada, 4905 Dufferin St, North York, ON M3H 5T4, Canada
  • 2Dept. Environmental Geochemistry, Institute for Geoecology, Technical University of Braunschweig, Langer Kamp 19c, 38106 Braunschweig, Germany

Abstract. Mercury (Hg) emitted from biomass burning is an important source of the contaminant to the atmosphere and an integral component of the global Hg biogeochemical cycle. In 2018, measurements of gaseous elemental Hg (GEM) were taken on-board a research aircraft along with a series of co-emitted contaminants in the emissions plume of an 88 km2 boreal forest wildfire on the Garson Lake Plain (GLP) in NW Saskatchewan, Canada. A series of four flight tracks were made perpendicular to the emissions plume at increasing distances from the fire each with 3–5 passes at different altitudes at each downwind location. The maximum GEM concentration measured on the flight was 2.88 ng m−3, which represents a ≈2.4x increase in concentration above background. GEM concentrations were significantly correlated with the co-emitted carbon species (CO, CO2, and CH4). Emissions ratios (ERs) were calculated from measured GEM and carbon co-contaminants data. Using the least uncertain of these ratios (GEM : CO), GEM concentrations were estimated at the higher 0.5 Hz time resolution of the CO measurements resulting in maximum GEM concentrations and enhancements of 6.75 ng m−3 and ≈5.6x, respectively. Extrapolating the estimated maximum 0.5 Hz GEM concentration data from each downwind location back to source, 1 km and 1 m (from fire) concentrations were predicted to be 12.9 and 29.9 ng m−3, or enhancements of ≈11x and ≈25x, respectively. ERs and emissions factors (EFs) derived from the measured data and literature values were also used to calculate Hg emissions estimates on three spatial scales: (i) the GLP fires themselves, (ii) all boreal forest biomass burning, and (iii) global biomass burning. The most robust estimate was of the GLP fires (21 ± 10 kg of Hg) using calculated EFs that used minimal literature derived data. Using a Top-down Emission Rate Retrieval Algorithm (TERRA) we were able to determine a similar emission estimate of 22 ± 7 kg of Hg. The elevated uncertainties of the other estimates and high variability between the different methods used in the calculations highlight concerns with some of the assumptions that have been used in calculating Hg biomass burning in the literature. Among these problematic assumptions are variable ERs of contaminants based on vegetation type and fire intensity, differing atmospheric lifetimes of emitted contaminants, the use of only one co-contaminant in emissions estimate calculations, and the paucity of atmospheric Hg species concentration measurements in biomass burning plumes.

David S. McLagan et al.

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Short summary
An assessment of mercury emissions from a burning boreal forest was made by flying an aircraft through its plume to collect in-situ gas and particulate measurements. Direct data show that in plume gaseous elemental mercury concentrations reach up to 2.4x background for this fire and up to 5.6x when using a correlation with CO data. These unique data are applied to a series of known empirical emissions estimates and used to highlight current uncertainties in the literature.
An assessment of mercury emissions from a burning boreal forest was made by flying an aircraft...
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