The entry of HCl into 60-68 wt % D2SO4 and HBr into 68 wt % acid containing 0-0.18 M 1-butanol was monitored by measuring the fractions of impinging HCl and HBr molecules that desorb as DCl and DBr after undergoing H -> D exchange within the deuterated acid. The addition of 0.18 M butanol to the acid creates butyl films that reach similar to 80% surface coverage at 213 K. Surprisingly, this butyl film does not impede exchange but instead enhances it: the HCl -> DCl exchange fractions increase from 0.52 to 0.74 for 60 wt % D2SO4 and from 0.14 to 0.27 for 68 wt % D2SO4. HBr -> DBr exchange increases even more sharply, rising from 0.22 to 0.65 for 68 wt % D2SO4. We demonstrate that this enhanced exchange corresponds to enhanced uptake into the butyl-coated acid for HBr and infer this equivalence for HCl. In contrast, the entry probability of the basic molecule CF3CH2OH exceeds 0.85 at all acid concentrations and is only slightly diminished by the butyl film. The OD groups of surface butanol molecules may assist entry by providing extra interfacial protonation sites for HCl and HBr dissociation. The experiments suggest that short-chain surfactants in sulfuric acid aerosols do not hinder heterogeneous reactions of HCl or HBr with other solute species.