Initial Findings of the African Combustion Aerosol Collaborative Intercomparison Analysis (ACACIA) Pilot Project

MEGAN MOUTON, Vaios Moschos, Marc Fiddler, Kyle Gorkowski, Abu Sayeed Md Shawon, Nevil Franco, Katherine Benedict, Barbara Turpin, Jason Surratt, Manvendra Dubey, Solomon Bililign, North Carolina A&T State University

     Abstract Number: 378
     Working Group: Carbonaceous Aerosol

Abstract
Biomass burning (BB) plays a vital role in the formation of climate-relevant atmospheric aerosols, whose optical properties are influenced by factors such as combustion type, chemical composition, and aging processes. In this study, we analyzed the optical properties of carbonaceous aerosols emitted from common sub-Saharan African biomass fuels, including acacia, eucalyptus, mopane, wanza, savanna grass, and cow dung.

The emissions were generated by burning these fuels under controlled conditions in a tube furnace. At North Carolina A&T State University (NCAT), combustion emissions entered a 9-m³ indoor smog chamber, while at Los Alamos National Lab (LANL), they were introduced into a 0.034-m³ mixing tube.

At NCAT, we measured light-extinction (scattering + absorption), scattering, and attenuation coefficients using a cavity ring-down spectrometer (CRDS), an integrating-sphere nephelometer, and a dual-spot aethalometer (AE33), respectively. We calculated mass-normalized coefficients, Ångström exponents, and optical-based emission factors. The intensive BB aerosol optical properties show considerable variability, influenced by factors such as fuel type, chamber relative humidity, and simulated aging in the presence of atmospheric oxidants and UV light.

At LANL, we employed the AE33, a cavity attenuated phase shift single-scattering albedo particle monitor (CAPS PMssa), and a photoacoustic soot spectrometer (PASS-3) to determine the BB aerosol optical properties and single scattering albedo (SSA, scattering/extinction ratio) at blue, green, and red wavelengths. We examined the dependence of the AE33 multiple-scattering correction factor on SSA and the impact of combustion type and aging degree on both variables. Wavelength dependence in SSA was observed in smoldering-dominated (less efficient) burns emitting high amounts of organic carbon.

By presenting and comparing the results from both laboratory analyses, we aim to address the knowledge gap concerning BB aerosol emissions in Africa, a region that has been underrepresented in prior research.