In eq. ( ), η0 is the viscosity at infinite temperature, Df is the fragility parameter, and T0 is the Vogel temperature. We assumed values of Df = 10 31,53-55 and η0 = 1 × 10 -5 . By inserting a viscosity of 1 × 10 9 Pa s and T = 20 °C (293 K) into Eq. 1, we calculated T0 to be -49 °C for catechol SOA. Using this value for T0 and our assumptions for Df and η0, the viscosity of catechol SOA was predicted at temperatures > 20 °C (Fig. ). At temperatures of 36 and 52 °C, the viscosities were greater than 1 × 10 6 Pa s and 1 × 10 4 Pa s, respectively (Fig. ). From the viscosity results shown in Fig. , we calculated the diffusion coefficient and mixing time of CO2 within the SOA. The calculated diffusion coefficient and mixing time of CO2 will be an upper limit to the diffusion coefficient and mixing time of acetone within the SOA since diffusion coefficients and mixing times are inversely related to the radius of the diffusion species.