As a case study to highlight the importance of LLPS and viscosity of BBOA, we focus on the heterogeneous reaction kinetics between ozone and BrC within BBOA. The BrC within BBOA can absorb solar radiation and lead to warming of the earth-atmospheric system . In the atmosphere, heterogenous reactions between ozone and BrC can lead to whitening . Recently, Schnitzler et al. showed that the whitening rate of BrC by ozone was strongly dependent upon the viscosity, with lifetimes of BrC (τBrC) in the upper troposphere extending to more than one day and τBrC in the planetary boundary layer less than one day . However, this study only investigated the properties of the water-soluble component of BBOA, which is analogous to studying only the hydrophilic phase in this work. Here we study how both LLPS and viscosity may impact the atmospheric lifetime of BrC in BBOA.