Recalcitrant Brown Carbon: Chemical Characteristics of Biomass Burning Organic Aerosol vs Soil Dust

RACHEL O'BRIEN, Janie (Yeaseul) Kim, Willow Hwang, Cassandra Gaston, Ann M. Dillner, Andrew P. Ault, Benjamin A. Nault, Manjula Canagaratna, Elise Palombella, Christopher Cappa, University of Michigan

     Abstract Number: 322
     Working Group: Remote and Regional Atmospheric Aerosol

Abstract
Brown carbon (BrC) in aerosol particles and cloud droplets can contribute to climate warming by absorbing solar radiation in the visible region of the solar spectrum. Large uncertainties remain in our parameterization of this warming, in part due to gaps in our knowledge of the atmospheric lifetimes of the light absorbing molecules in the mixtures. An important removal pathway includes chemical transformations that fragment the chromophore, thus removing its ability to absorb visible light. BrC is emitted from solid fuel combustion like wildfires (biomass burning organic aerosol, BBOA) and it can also be found in soil derived aerosol particles. A fraction of BrC from wildfires has been found to retain its brown color for days or longer in the atmosphere. The longer-term behavior of the BrC from soil derived aerosol is not well characterized, but we expect it to also retain some color. The characteristics of this recalcitrant material are important to characterize because it can contribute to warming long after the more photolabile portion has bleached. Here we characterize the chemical composition of soil derived dust samples and evaluate the extent to which soil dust is representative of the recalcitrant brown fraction of BBOA collected from smoldered samples generated in lab (pine, oak) as well as aerosol particles collected in Barbados after transport from Africa in a biomass burning plume.