Evolution of Black Carbon upon Coating at the Wildland-Urban Interface with Biomass Burning Organic Aerosol Versus Coatings of Volatile Chemical Products in Urban Environments

CHRISTIAN ESCRITT, Katrina Betz, Micah Miles, Elijah Schnitzler, Oklahoma State University

     Abstract Number: 91
     Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires

Abstract
As the instances of severe wildfire increase across much of the US, the interactions between emissions of biomass burning and urban sources at the wildland-urban interface (WUI) become more critical to air quality and climate change. In the urban environment, uncoated aggregates of black carbon (BC), which initially have fractal branched morphologies, are commonly emitted from diesel engines. When biomass burning emissions are transported across the WUI, these BC aggregates are exposed to biomass burning organic aerosol (BBOA), composed of many compounds with wide ranges of chemical, physical, and optical properties, including volatility. The components of BBOA will partition onto the BC aggregates, and the resulting coatings will cause changes to the aggregates, specifically, compacting them into more sphere-like morphologies as well as changing the hygroscopicity of BC, which impacts its interactions with radiation and clouds. Here, we investigate the effects of different volatility fractions of BBOA, representative of different ages of plumes with respect to dilution in the atmosphere, on BC restructuring. From series of diameter growth factors for coated and coated-denuded BC particles, we determine that, as volatility decreases, more coating is necessary for the same amount of restructuring. This is two-fold because, as the plume travels and becomes lower volatility, less overall material is present in the plume. In urban environments, volatile chemical products (VCP) are also a significant source of organic compounds. Geranyl esters are representatives of these compounds, and we show they are extremely efficient at restructuring BC, due to their physicochemical properties (e.g., volatility). We will discuss the results and their implications in the context of previous studies of BC restructuring. Broadly, our observations indicate that fresh wildfire plumes may have more potential to impact the morphology of BC at the WUI while low concentrations of VCP can restructure BC in urban environments.