Abstract. There are many fuels used for domestic purposes in east Africa, producing a significant atmospheric burden of the resulting aerosols, which includes biomass burning particles. However, the aerosol physicochemical properties are poorly understood. Here, combustion of Eucalyptus and Acacia fuels was performed at 500 and 800 °C in a tube furnace, followed by immediate filter collection for fresh samples or introduction into a photochemical chamber to simulate atmospheric photochemical aging under the influence of anthropogenic emissions. The aerosol generated in the latter experiment was collected onto filters after 12 hours of photochemical aging. 500 and 800 °C were selected to simulate smoldering and flaming combustion, respectively, and to cover a range of combustion conditions. Methanol extracts from Teflon filters were analyzed by ultra-performance liquid chromatography interfaced to both a diode array detector and an electrospray ionization high-resolution quadrupole time-of-flight mass spectrometer (UPLC/DAD-ESI-HR-QTOFMS) to determine the light-absorption properties of biomass burning organic aerosol constituents chemically characterized at the molecular level. Few chemical or UV/Visible differences were apparent between samples for either fuel when combusted at 800 °C. Differences in single scattering albedo (SSA) between fresh samples at this temperature were attributed to compounds not captured in this analysis, with eucalyptol being one suspected missing component. For fresh combustion at 500 °C, many species were present, where lignin pyrolysis and distillation products are more prevalent in Eucalyptus, while pyrolysis products of cellulose and at least one nitroaromatic species were more prevalent in Acacia. SSA trends are consistent with this, particularly if the absorption of those chromophores extends to the 500–570 nm region. Upon aging, both show that resorcinol or catechol was removed to the highest degree, and both aerosol types were dominated by loss of pyrolysis and distillation products, though both differed in the specific compounds being consumed by the photochemical aging process.

<p><strong>Abstract.</strong> An accurate measurement of optical properties of aerosols is critical for quantifying the effect of aerosols on climate. Uncertainties persist and measurement results vary significantly. Biomass burning (BB) aerosols have been extensively studied through both field and laboratory environments for North American fuels to understand the changes in optical and chemical properties as a function of aging. There is a clear research need for a wider sampling of fuels from different regions of the world for laboratory studies. This work represents the first such study the optical and chemical properties of three wood fuel samples used commonly for domestic use in east Africa. In general, combustion temperature plays a major role on the optical properties of the emitted aerosols. For fuels combusted at 800 °C SSA values are in the range between 0.287 and 0.439 while the SSA for fuels combusted at 500 °C, the range between 0.66 and 0.769. There is a clear but very small dependence of SSA on fuel type, with eucalyptus producing aerosol with higher SSA than olive and acacia. A significant increase in the scattering and extinction cross-section (mostly dominated by scattering) was observed, indicating the occurrence of chemistry, even during dark aging for combustion at 500 °C. This fact can't be explained by the heterogeneous chemistry and we hypothesized secondary organic aerosol formation as a potential phenomenon happing during dark aging. After 12 h of photochemical aging, BB aerosol becomes highly scattering with SSA values above 0.9, which can be attributed to oxidation in the chamber. Due to the very low number concentration of aerosols during aging studies of combustion at 800 °C, the results were inconclusive. We also attempted to simulate polluted urban environments by ejecting VOCs and BB aerosol into the chamber, but no distinct difference was observed, since measurements were done 12 hours after injection of VOCs.</p>

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