Abstract Number: 269 Working Group: Carbonaceous Aerosol
Abstract Soot particles, emitted into the atmosphere during combustion of carbonaceous material, often internally mix with secondary organic aerosol. The distribution of the mixing components within each soot particle affects its optical properties and therefore the soot radiative forcing. We performed an electron microscopy analysis of particles collected in a biogenically-dominated environment in Cool, California, during the Carbonaceous Aerosols and Radiative Effects Study (CARES), in 2010. The goal was to unveil relations between different soot mixing configurations and the viscosity of the mixing organic material. Because viscous particles deform upon impaction on a substrate - with the degree of deformation depending on their viscosity - we used tilted electron microscopy images to classify the organic particles into low, intermediate, and high viscosity groups based on their aspect ratio. We found that organic material in the intermediate viscosity regime almost always partially engulfed the soot particles they mixed with (90% by number). Highly viscous organic aerosol instead remained externally mixed with, or attached on the surface of, the soot particles. The viscosity of organic aerosol depends on temperature, humidity, and the material chemical composition; therefore, our findings can help model the mixing configuration of soot at given atmospheric conditions to improve the estimates of the soot impact on climate.