.: T50 values of microplastics suspension samples and water blank with 83% confidence intervals. Two datasets are statistically distinct with a 95% confidence level if their respective 83% confidence bands do not overlap . Overall, exposure to O3 or UVC+O3 (referred to as photooxidation hereafter) either caused no change (i.e. the change was less than the uncertainties of the measurements) or a decrease in ice nucleation activity. For the non-ice nucleation active plastics (PP-spheres c , PET-spheres c , PEspheres c , PE-flakes b ) no statistically significant change in ice nucleation activity was observed after exposure to O3 or photooxidation. A similar result was observed for the ice-active sample PP-fibers b (i.e. no change was observed). On the other hand, for the ice nucleation active samples PP-needles c and PET-fibers b , nucleation temperatures decreased slightly after exposure to O3 and more strongly after photooxidation.