The temperature and RH in the troposphere can vary from approximately 200 K to 300 K and 10% to 100%. To parameterize the measurements of viscosity of the two phases in BBOA as a function of both RH and temperature, we combine the Arrhenius mixing rule expression with the Vogel-Fulcher-Tamman equation (Section S2). The temperature-and RH-dependent viscosities of the hydrophilic and hydrophobic phases in BBOA are reported in Fig. and. The viscosity of the hydrophilic phase shows a strong dependence on both the temperature and the RH, similar to the viscosity of the water soluble component of BBOA and secondary organic aerosol observed in other studies . In sharp contrast, the viscosity of the hydrophobic phase is largely independent of the RH between values from 0 to approximately 95% at all temperatures. For temperatures between 293 K and 230 K, the hydrophobic phase is semisolid (viscosity > 10 2 Pa s) for all RH values below 95%, and for colder temperatures the hydrophobic state is glassy (viscosity > 10 12 Pa s) at all RHs below 95%. Although previous studies have identified that atmospheric aerosol can exhibit glassy states at low temperatures and low RHs , to our knowledge this is the first study to show glassy states could be present in atmospheric aerosol at RHs as high as 95%. Furthermore, for numerous temperatures and at higher RH conditions, the viscosity of the hydrophobic phase can be many orders of magnitude higher than that of the hydrophilic phase, as evidenced in the plot of the viscosity difference between the two phases in Figure .