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Abstract. An accurate measurement of the optical properties of aerosol is critical for quantifying the effect of aerosol on climate. Uncertainties persist and results of measurements vary significantly. Biomass burning (BB) aerosol has been extensively studied through both field and laboratory environments for North American fuels to understand the changes in opticaland chemical properties as a function of aging. There is a need for a widersampling of fuels from different regions of the world for laboratory studies. This work represents the first such study of the optical andchemical properties of wood fuel samples commonly used for domestic purposes ineast Africa. In general, combustion temperature or modified combustionefficiency (MCE) plays a major role in the optical properties of the emitted aerosol. For fuels combusted with MCE of 0.974±0.015, which is referred to as flaming-dominated combustion, the single-scattering albedo (SSA) values were in the range of 0.287 to 0.439, while for fuels combusted with MCE of 0.878±0.008, which is referred to as smoldering-dominated combustion, the SSA values were in the range of 0.66 to 0.769. There is a clear but very small dependence of SSA on fuel type. A significant increase in the scattering and extinction cross section (with no significant change inabsorption cross section) was observed, indicating themore »occurrence of chemistry, even during dark aging for smoldering-dominated combustion. Thisfact cannot be explained by heterogeneous oxidation in the particle phase,and we hypothesize that secondary organic aerosol formation is potentiallyhappening during dark aging. After 12 h of photochemical aging, BB aerosolbecomes highly scattering with SSA values above 0.9, which can be attributedto oxidation in the chamber. Aging studies of aerosol from flaming-dominatedcombustion were inconclusive due to the very low aerosol number concentration. We also attempted to simulate polluted urban environments byinjecting volatile organic compounds (VOCs) and BB aerosol into the chamber, but no distinct difference was observed when compared to photochemical aging in the absence of VOCs.« less

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, the combustion of eucalyptus, acacia, and olive 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 h 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 (UV: ultraviolet) differences were apparent between samples for the fuels 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 suspectedmore »missing component. For fresh combustion at 500 ∘C, many species were present; lignin pyrolysis and distillation products are more prevalent in eucalyptus, while pyrolysis products of cellulose and at least one nitro-aromatic species were more prevalent in acacia. SSA trends areconsistent with this, particularly if the absorption of those chromophoresextends to the 500–570 nm region. Upon aging, both show that resorcinolor catechol was removed to the highest degree, and both aerosol types weredominated by loss of pyrolysis and distillation products, though they differed in the specific compounds being consumed by the photochemical aging process.« less