Brown carbon emissions from laboratory combustion of Eurasian arctic-boreal and South African savanna biomass

Abstract. Warming climate is predicted to increase forest fires which can be a major source of black and brown carbon (BC and BrC) into the atmosphere. Unlike North American forest fires, very limited studies have characterized North Eurasian biomass burning (BB) emissions. In this work, we defined the emission factors of carbonaceous aerosols and characterized light absorption of BrC emitted from boreal and peat burning through offline filter extraction method. The results were compared to African savanna emissions. Effects of atmospheric dilution and oxidative aging on BrC absorptivity were investigated for selected BB emissions sampled into an environmental chamber. Organic carbon (OC) and elemental carbon (EC) emission factors of fresh BB emissions ranged between 1.30–89.9 g kg^-1 and 0.01–4.80 g kg^-1 respectively. Methanol soluble OC (MSOC) represented more than 92 % of fresh BB emissions but intrinsic chemical differences among samples resulted in MAC_MSOC values ranging from 0.46–1.48 m² g^-1 at 365 nm. Fresh BB emissions formed weakly absorbing BrC with k_{550_MSOC} ranging from 0.002 and 0.011. Water soluble OC (WSOC) fractions varied among fresh BB emissions but overall exhibited higher MAC₃₆₅ than MSOC. Dilution-related evaporative loss in environmental chamber resulted in less volatile OC, making them less soluble in methanol. Photochemical and dark oxidative aging further increased the ELVOC fraction of the organics along with oxidation state. Our estimated OC-EC emission factors and k_MSOC for fresh BB emissions can be used for future modelling purposes. Further online measurements are needed to account for non-soluble strong BrC in aged BB emissions.