Probing rBC-containing particle morphology with a single-particle soot photometer (SP2)

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Description

Knowledge of the structure and mixing state of black-carbon-containing particles is important for calculating their radiative forcing and provides insight into their sources and life cycles. Recent analysis of the single-particle signals from a single-particle soot photometer (SP2) instrument for black-carbon-containing particles has identified a significant fraction where the black carbon component may reside on or near the surface of the particle as opposed to in a core-shell configuration. Traditionally, core-shell configurations are assumed in which the black carbon core is surrounded by a shell of non-refractory material. During the DOE-sponsored Aerosol Life Cycle field campaign held in summer 2011 at Brookhaven National Laboratory on Long Island, New York, episodes were encountered in which a high fraction of particles containing black carbon had such configurations. These episodes corresponded to air masses that contained biomass burning plumes (Sedlacek et al. 2012). Subsequent analysis found similar episodes in additional field campaigns in Colorado and California in which high fractions of black-carbon-containing particles exhibited a similar configuration. These episodes also corresponded to biomass burning plumes. In an effort to evaluate this interpretation and explore formation mechanisms for these types of particle morphologies, a series of laboratory-based experiments examining the coagulation of Regal black (surrogate for collapsed soot) with model non-refractory coatings dioctyl sebacate (surrogate for organic aerosols with liquid-like character) and deliquesced ammonium sulfate (solid) were carried out. The results of these experiments and their potential implications on black carbon radiative forcing will be discussed. In addition to the laboratory study, preliminary analysis from the summer portion of the Two-Column Aerosol Project (TCAP) field campaign will also be presented.

Sedlacek III, Arthur, ER Lewis, LI Kleinman, J Xu, and Q Zhang. 2012. “Determination of and Evidence for Non-core-shell structure of particles containing black carbon using the single particle soot photometer (SP2).” Geophysical Research Letters 39: L06802, doi:10.1029/2012GL050905.