We assumed that BBOA forms a single phase when mixed with H2SO4. Previous studies have shown that when secondary organic aerosol with an average O/C ratio ≳ 0.8 is mixed with ammonium sulfate aerosols, the resulting particles form a single phase. Studies are needed to confirm if a similar threshold applies for BBOA mixed with H2SO4. 3) To calculate the viscosity of BBOA particles from their glass transition temperatures, we assumed a fragility parameter (D) of 10, consistent with values used in previous studies. Measurements are needed to confirm that a fragility of 10 is appropriate for BBOA. 4) To calculate the viscosity of aged BBOA-H2SO4 particles, we used the ZSR method and the AIOMFAC-VISC thermodynamic model. Observations are needed to confirm the validity of this approach specifically for laboratory-generated and field-collected BBOA-H2SO4 particles.