Near Infrared-Absorbing, Non-Black Carbon Particulate Material from Biomass Burning
TIMOTHY ONASCH, Ernie R. Lewis, Arthur J. Sedlacek,
Aerodyne Research, Inc. Abstract Number: 398
Working Group: Carbonaceous Aerosol
AbstractBiomass burning produces two classes of light absorbing particles: black carbon (BC) and light- absorbing organic commonly referred to as brown carbon (BrC). BC particles absorb throughout UV, visible, and near-IR wavelengths, whereas BrC particles absorb mainly in the UV-VIS. Recent field and laboratory studies have identified, and begun to quantify, BrC that absorbs light from the UV-VIS out to the near infrared (NIR), which we call NIR-BrC. Examples of such particles are tar balls and BrC strongly associated with BC. NIR absorption by organic material from biomass burning represents a positive longwave radiative forcing. For example, while BC has an approximately 10x greater mass absorption cross-section than tar balls at 950 nm, tar balls can be present in near-source biomass burning plumes at 5-10x greater mass concentrations than BC, resulting in roughly the same absorption by both types of particles at 950 nm.
The Soot Particle Soot Photometer (SP2) can be utilized to detect NIR absorption by NIR-BrC particles. Here we are working to extend the novel SP2 analysis technique described by Corbin and Gysel (2019), which uses the time series of the scattering signal of non-BC-containing particles to determine if absorption of the 1064 nm laser energy results in particle shrinkage. We are applying this technique to ground-based SP2 measurements of smoke plumes collected as part of the 2019 FIREx campaign. This technique offers the unique potential for providing particle-resolved measurements of NIR-BrC, an estimate of the fraction of OA that absorbs in the NIR, and a basis for delineating the NIR absorption contributions between BC and NIR-BrC. These observations may provide an important quantitative assessment of NIR-BrC particles and their importance to radiative forcing.