In this work, we report that methyl-substituted succinic acid present at or near the surface of aqueous organic droplets can be efficiently oxidized by gas-phase OH radicals. The alkoxy radical chemistry appears to be an important reaction pathway. In addition, our model simulations reveal the relative importance of functionalization and fragmentation processes, alongside volatilization, in the evolution of the particle-phase reaction, which is largely dependent on the extent of oxidation.