N.C. A&T, LANL Study Optical Properties of Aerosols from African Biomass Fuel Burning

EAST GREENSBORO, N.C. (June 9, 2023) – Research teams from North Carolina Agricultural and Technical State University and Los Alamos National Laboratory (LANL) in New Mexico have initiated the first phases of the African Combustion Aerosol Collaborative Intercomparison Analysis (ACACIA) pilot study. The project titled “Studies of optical and chemical properties of aged and fresh biomass burning absorbing aerosols for climate models” is funded by the Department of Energy.

Principal investigator (PI) Solomon Bililign, Ph.D., a professor in N.C. A&T’s departments of physics and applied science and technology (AST), co-PI Marc Fiddler, Ph.D., and LANL lab group leader Manvendra Dubey, Ph.D., established the collaboration, enhancing the university’s leading expertise in air quality and African biomass fuel burning through the use of LANL’s advanced instrumentation to validate measurements taken at the university’s laboratory.

Although the research project focuses on burning biomass fuels native to Africa – the least-studied region in the world – the findings also will inform global air pollution implications and strategies, since wildfires affect various areas.

“The work in our group looks at detailed characterization of the chemical composition and their light-absorbing scattering properties to be able to understand their impact on health and climate,” Bililign noted in the grant’s abstract.

This project also creates opportunities for team members like Vaios Moschos, Ph.D., an A&T postdoctoral research fellow and LANL visiting scientist, and Megan Mouton, an AST Ph.D. candidate, to enhance their research portfolios while collaborating with other experts at a national laboratory. The pair visited LANL for two weeks in the spring. Moschos designed the experiments, while Mouton was responsible for analyzing the optical measurements.

The first phase of the ACACIA pilot study included “analyzing particle emissions produced by burning multiple African biomass fuels at LANL – including acacia, eucalyptus, mopane, wanza, cow-dung and savanna grass that have a moisture content below 15% as measured at LANL – and focusing on various combustion conditions, by adjusting the temperature of a tube furnace, according to gas analyzer data and modified combustion efficiency calculations.”

LANL postdoctoral research associates Kyle Gorkowski, Ph.D., and Abu Sayeed Md Shawon, Ph.D., were responsible for overseeing the combustion system and operating the LANL instruments and were assisted by postdoctoral researcher Nevil A. Franco, Ph.D.

Here are the team’s reported methods and initial findings:

• The team employs the photoacoustic soot spectrometer (PASS-3) and the Cavity Attenuated Phase Shift single-scattering albedo monitor (CAPS PMssa) to gather data on the light absorption and scattering properties of the generated primary particles. This information enables the calculation of the single-scattering albedo (SSA) at three wavelengths (blue, green, red).
• Moschos measures light transmission through particle-laden filters using a dual-spot aethalometer (AE33) and converts the data into light-attenuation coefficients. He compares the filter-based findings with in situ absorption measurements to establish AE33 calibration coefficients, which account for apparent absorption due to multiple scattering artifacts, and further examines the influence of experimental conditions on these correction factors.
• Moschos initially hypothesized that the AE33 multiple scattering correction is influenced by aerosol size, composition, aging, and morphology. He aims to assess the calibration coefficients' wider applicability in various environments since the AE33 is ideal for long-term unattended measurements and has recently proven its effectiveness and robustness in an N.C. A&T lab campaign.
• During the first week of the two-week visit, the researchers discovered that the SSA depends on wavelength in smoldering burns but not in flaming-dominated burns. The initial hypothesis was validated, showing that the AE33 calibration is influenced by combustion conditions and chemical composition, with higher values observed in smoldering burns. The relationship between AE33 calibration coefficients and SSA is currently being examined.
• In the second week, the team investigated black carbon formation in mixed-combustion and flaming-dominated burns using a single-particle soot photometer (SP2), according to Katherine Benedict,D., a research scientist at LANL. The team further performs aging experiments on selected African fuel-derived primary combustion emissions using an oxidation flow reactor.

The team will share these initial findings at The American Association for Aerosol Research Conference in Portland, Oregon this fall. Bililign and Fiddler will initiate the pilot’s second phase with MarkieSha James, an AST applied chemistry Ph.D. candidate, by visiting LANL for a new measurement campaign this July.