One geoengineering mitigation strategy for global temperature rises is to inject particles into the stratosphere to scatter solar radiation back to space. However, the injection of such particles must not perturb ozone. We measured the rate of uptake of HO₂ radicals, an important stratospheric intermediate, onto TiO₂ particles. Using the atmospheric model TOMCAT, we showed that surface reactions between HO₂ and TiO₂ would have a negligible effect on stratospheric concentrations of HO₂ and ozone.