Wavelength and Particle Mass-dependent Optical Profiles of Aerosols from Burning African Biomass

Africa is a significant and growing source of biomass burning (BB) emissions. Particulate matter from burning fuels for heating and cooking affects air quality, human health, and the climate. During the African Combustion Aerosol Collaborative Intercomparison Analysis (ACACIA) pilot study at Los Alamos National Laboratory, we examined the optical properties of BB aerosol produced from combusting authentic African fuels under smoldering conditions. Fuels were burnt in a tube furnace at 450 ^oC and sampled through a stainless-steel mixing tank. Particle mobility diameter was selected with a differential mobility analyzer, and selection for particle mass-to-charge used an aerosol mass analyzer. The concentration of these mass and size-selected particles was measured with a condensation particle counter, and they were characterized for their optical properties at wavelengths of 405, 450, and 532 nm. This setup allowed for calculating optical mass cross sections as a function of particle mass. Preliminary data exhibits a linear relationship between particle optical cross section and particle mass, yielding a mass scattering coefficient of (2.1±0.1) • 10^–15 and (4.5±0.3) • 10^–15 m²/fg for Mopane leaves and Mukuzi hardwood, respectively, at 450 nm. Additional results for BB aerosol from Mosetlha, Mokala, and wild Olive will be presented.

This work will also present results for the single scattering albedo, extinction emission factor, and mass scattering, absorption, and extinction cross-section as a function of wavelength and modified combustion efficiency. This work was done using the NCA&T smog chamber, where aerosol optical properties were characterized using a combination of aethalometry, nephelometry, and cavity ring-down spectroscopy. This chamber allows for studying the effects of dark and photochemical aging and the effects of humidification on aerosol properties.

This was supported by the Department of Energy award DE-SC0023051 and we acknowledge Dr. Gizaw Mengistu Tsidu at BIUST for providing biomass fuel samples from Botswana.