PNNL

Abstract

Atmospheric soot particles are often internally mixed with secondary organic aerosol (SOA). Spatial distribution of the mixing components affects the soot particles’ radiative properties. Here, we present an electron microscopy analysis of particles collected in a biogenic environment, aiming to understand how the viscosity of SOA relates to various soot mixing configurations. The shape of particles impacting on a substrate deforms according to their viscosity. We use the aspect ratio of individual particles determined by tilt angle imaging to classify them into low, intermediate, and high viscosity groups. The organic material partially engulfing soot is of intermediate viscosity for ~90% of the particles containing soot. In contrast, the highly viscous organic aerosol remain externally mixed with or attach to the surface of soot particles. Our results link the viscosity of organic aerosol with the mixing configuration of soot-containing particles, and could help improve the estimate of the soot radiative forcing.