Atmos. Chem. Phys. Discuss., 13, 14069-14114, 2013
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Airborne observations of trace gases over boreal Canada during BORTAS: campaign climatology, airmass analysis and enhancement ratios
S. J. O'Shea1, G. Allen1, M. W. Gallagher1, S. J.-B. Bauguitte2, S. M. Illingworth1, M. Le Breton1, J. B. A. Muller1, C. J. Percival1, A. T. Archibald3, D. E. Oram4, M. Parrington5, P. I. Palmer5, and A. C. Lewis6
1School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
2Facility for Airborne Atmospheric Measurements (FAAM), Building 125, Cranfield University, Cranfield, Bedford, MK43 0AL, UK
3Centre for Atmospheric Science, University of Cambridge, Cambridge CB2 1EW, UK
4National Centre for Atmospheric Science, School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
5School of GeoSciences, The University of Edinburgh, Edinburgh, UK
6National Centre for Atmospheric Science (NCAS), University of York, Heslington, York YO10 5DD, UK

Abstract. In situ airborne measurements were made over Eastern Canada in summer 2011 as part of the BORTAS experiment (Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and~Satellites). In this paper we present observations of greenhouse gases (CO2 and CH4) and other biomass burning tracers and related trace gases, both climatologically and through case studies, as recorded on board the FAAM BAe-146 research aircraft. Vertical profiles of CO2 were generally characterised by depleted boundary layer concentrations relative to the free troposphere, consistent with terrestrial biospheric uptake. In contrast, CH4 concentrations were found to rise with decreasing altitude due to strong local and regional surface sources. We use coincident tracer-tracer correlations and a Lagrangian trajectory model to characterise and differentiate air mass history of intercepted plumes. In particular, CO, HCN and CH3CN were used to identify air masses that have been recently influenced by biomass burning. Concentrations of CO2 were found to have a mean tropospheric, campaign-average concentration of 384.8 ppm (ranging between 371.5 and 397.1 ppm), whilst CH4 concentrations had a mean value of 1859 ppb (ranging between 1797 and 1968 ppb), representing the episodic sampling of local fire plumes. CH4 and CO2 concentrations during BORTAS were found to be broadly comparable to previous measurements in the region during the regional burning season and with reanalysed composition fields from the EU Monitoring Atmospheric Composition and Change (MACC) project. By examining individual case studies we were able to quantify emissions from biomass burning. Using both near-field (<1 day) and far-field (>1 day) sampling, boreal forest fire plumes were identified throughout the troposphere. Fresh plumes from fires in Northwest Ontario yield emission factors for CH4 and CO2 of 8.5 ± 0.9 g (kg dry matter)−1 and 1512 g ± 185 g (kg dry matter)−1, respectively. We have also investigated the efficacy of calculating emission factors from far-field sampling, in which there might be expected to be limited mixing with background and other characteristic air masses and we provide guidance on best practice and limitations in such analysis. We have found that for measurements within plumes that originated from fires in Northwest Ontario 2–4 days upwind, emission factors can be calculated that range between 1618 ± 216 and 1702 ± 173 g (kg dry matter)−1 for CO2 and 1.8 ± 0.2 and 6.1± 1 g (kg dry matter)−1 for CH4.

Citation: O'Shea, S. J., Allen, G., Gallagher, M. W., Bauguitte, S. J.-B., Illingworth, S. M., Le Breton, M., Muller, J. B. A., Percival, C. J., Archibald, A. T., Oram, D. E., Parrington, M., Palmer, P. I., and Lewis, A. C.: Airborne observations of trace gases over boreal Canada during BORTAS: campaign climatology, airmass analysis and enhancement ratios, Atmos. Chem. Phys. Discuss., 13, 14069-14114, doi:10.5194/acpd-13-14069-2013, 2013.
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