The kinetic multilayer model of gas-particle interactions in aerosols and clouds (KM-GAP) was used to simulate the uptake of ozone by BBOA particles and to determine the lifetime (i.e. e-folding timescale) of BrC within BBOA due to oxidative aging by ozone. The full description of this model can be found in , but a brief description is given here as well as a description of the updates for this implementation. KM-GAP consists of multiple model layers including a gas phase, a near-surface gas phase, a sorption layer, a near-surface bulk layer, and a number of bulk layers. KM-GAP explicitly treats the processes of gas-phase diffusion, adsorption and desorption, surface-to-bulk transport and bulk diffusion within the particle. In this work, for phase-separated particles, bulk mass transport includes transport between layers within each phase as well as transport between the two phases. Because the simulation scenarios included a hydrophilic core at very low RH, the original KM-GAP model was updated to include multiple core layers to account for potential diffusion limitations. Here we use 10 total layers in all simulations. In the phase-separated cases, these are divided as 5 layers in the shell phase and 5 layers in the core phase. Chemical reactions of ozone and BrC were treated in both phases. Kinetic parameters used in the simulations are given in Table . The product of the reaction between BrC and ozone was assumed to have the same properties as the BrC and the rest of the particle consists of non-reactive and non-volatile species. To quantify the lifetime of BrC, τBrC, we use the e-folding timescale, which represents the time it takes for the amount of BrC to reach 1/e of its final value relative to its initial value in the whole particle.