Production of peroxy nitrates in boreal biomass burning plumes over Canada during the BORTAS campaign

Abstract. The observations collected during the BORTAS campaign in summer 2011 over Canada are analysed to study the impact of forest fire emissions on the formation of ozone (O3) and total peroxy nitrates (ΣPNs, ΣROONO2). The suite of measurements on board the BAe-146 aircraft, deployed in this campaign, allows us to calculate the production of O3 and of ΣPNs, a long lived O3 reservoir whose concentration is supposed to be impacted by biomass burning emissions. In fire plumes, profiles of carbon monoxide (CO), which is a well-established tracer of pyrogenic emission, show concentration enhancements that are in strong correspondence with a significant increase of ΣPNs concentrations, whereas minimal increase of the concentrations of O3 and NO2 are observed. In those fire plumes the average ΣPNs production is 12 times greater than in the background plumes, by contrast the average O3 production is only 5 times greater. These results suggest that, at least for boreal forest fires and for the measurements recorded during the BORTAS campaign, fire emissions impact both the oxidized NOy and O3, but: (1) ΣPNs production is affected significantly respect to the O3 production and (2) in the forest fire plumes the ratio between the ΣPNs production and the O3 production is lower than the ratio evaluated in the background air masses, thus confirming that the role played by the ΣPNs produced during biomass burning is significant in the O3 budget. These observations are consistent with elevated production of PAN and concurrent low production (or sometimes loss) of O3 observed in some another campaigns (i.e. ARCTAS-B) focused on forest fire emissions. Moreover our observations extend ARCTAS-B results since PAN is one of the compounds included in the ΣPNs family detected during BORTAS. The implication of these observations is that fire emissions in some cases, for example Boreal forest fires and in the conditions reported here, may influence more long lived precursors of O3 than short lived pollutants, which in turn can be transported and eventually diluted in a wide area. These observations provide additional indirect evidence that O3 production may be enhanced as plumes from forest fires age.

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