The glass transition temperature of dry BBOA (Tg,BBOA) and the volume-based hygroscopicity parameter of the BBOA (κ) have been reported for several types of unaged BBOA (Table ). The variability in Tg,BBOA and κ is likely due to differences in experimental conditions used to generate and sample the BBOA, such as the fuel type, combustion conditions, and dilution. Here we calculated the viscosity of unaged BBOA using each of the Tg,BBOA and κ pairs shown in Table to determine the possible range of viscosities and phase states of unaged BBOA in the stratosphere.