Laboratory studies of fresh and aged biomass burning aerosols emitted from east African biomass fuels – Part 1 – Optical properties

Abstract

<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>

Impact of combustion conditions on physical and morphological properties of biomass burning aerosol

“…This work was conducted at the North Carolina Agricultural and Technical State University (NCAT) indoor burning facility that has a well-equipped environmental chamber for the measurement of fresh and aged aerosol, which is described in detail elsewhere (Smith et al 2019(Smith et al , 2020a(Smith et al , 2020b. BB aerosol was generated by the combustion of biomass fuel in a tube furnace.…”