Laboratory Experiments on Savannah and European Boreal Forest Fire Emissions

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Abstract Landscape fire is among the largest sources of aerosols and trace gases globally. However, the emissions are highly variable and strongly affected by the type of biomass and combustion characteristics. We investigated the effect of combustion characteristics on the burning emissions from three biomass types: woody plants and grasses from southern African savannah and European boreal forest surface based on experiments at the ILMARI combustion facility in Kuopio, Finland. Considering emission factors (EF) for organic aerosol (OA) and for the sum of volatile organic compounds (VOCs), we observed a linear increase in the EF with decreasing modified combustion efficiency (MCE) down to MCE of 0.6. For instance, for woody plants from savannah flaming combustion EF OA is 6.1 g kg −1 at MCE of 0.94, while extreme smoldering EF OA at MCE of 0.67 is 54 g kg −1 . Interestingly, the effect of biomass type was minor compared to MCE, which was also seen for aerosol particle number size distributions. Likewise, the absorption Ångström exponent increased with decreasing MCE. Furthermore, OA in our experiments is absorbing not only at the short wavelengths, which is typical of brown carbon, but even at the longest wavelengths (880 and 950 nm), which are often considered to represent only absorption by black carbon. The biomass type impacted the OA and VOC composition, especially in higher O:C ratio for savannah grass emissions, irrespective of combustion characteristics.

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