Lawrence Berkeley National Laboratory

The size and thickness of organic aerosol particles from five field campaigns were compared to those of laboratory generated secondary organic aerosols (SOA) using scanning transmission x-ray microscopy (STXM). Impacted organic particles were identified and the total carbon absorbance (TCA) was analyzed as a function of the area equivalent diameter of the particle on the substrate. Because they flatten less upon impaction, particles with higher viscosity and surface tension can be identified by a steeper slope on a plot of TCA vs. size. The slopes of the ambient data are statistically similar indicating a small range of average viscosities and surface tensions across five field campaigns. Steeper slopes were observed for the plots corresponding to ambient particles, while smaller slopes were indicative of the laboratory generated SOA. This suggests that, on average, ambient organic particles have higher viscosities and surface tensions than the more liquid like laboratory generated SOA particles.