Viscosities extended beyond 10 20 Pa s, however the y-axis was capped at this value. Shown in Figure are the calculated viscosities for the 10 unaged BBOA types listed in Table . Similar to Figure , we carried out calculations for the stratosphere at altitudes of 15 and 32 km and a water vapour mixing ratio of 15 ppmv. For the temperature range of 200 -250 K, all the BBOA types have viscosities of approximately 10 7 Pa s or greater (Fig. ). These extremely high viscosities are due to a combination of low RH values and low temperatures (Fig ). Furthermore, 8 out of the 10 BBOA types exhibit viscosities exceeding 10 12 Pa s for the entire temperature range of 200 -250 K, indicating that they are predicted to remain in a glassy solid state throughout this range. For the 2 proxies studied by Gregson et al. a glassy solid state was observed over a narrower range of temperatures (200 -230 K for the hydrophobic phase and 200 -240 K for hydrophilic phase), but the glassy state still dominated between 200 -250 K. Overall, these results suggest that the glass state dominates for unaged BBOA in the stratosphere for the 200 -250 K temperature range. At temperatures ≲ 200 K all of the BBOA types switch from a glassy solid state to a semisolid or liquid state (Fig. ) due to the heightened RH in this low-temperature regime (Figure ). At an altitude of 15 km, the transition from a glassy state to a semisolid/liquid state occurs at about 195 -200 K. At an altitude of 32 km, the transition occurs at about 180 -185 K.