O3 exposure did not cause a detectable change in the chemical or morphological properties of the ice-active microplastics (PP-fibers b , PP-needles c , and PET-fibers b ) (Table , column 3 and column 4). On the other hand, O3 exposure caused a decrease in ice nucleation ability of the PPneedles c and PET-fibers b (Table , column 2). We conclude that O3 exposure must have caused some chemical and/or physical changes at the surface of the PP-needles c and PET-fibers b that were not detected with FTIR or SEM measurements. Future studies that use surface-focused analytical techniques, such as X-ray photoelectron spectroscopy for example, are needed to understand the relationship between O3 exposure and ice nucleation ability of microplastics.