A study of the change of the ice nucleating ability of biological particles by atmospheric oxidants is presented. For this, particles derived from SNOMAX® bacteria and birch pollen were exposed to hydroxyl radical (OH) and ozone (O3) in a flow tube and environmental chamber, and ice nucleation activity was measured using a flow diffusion chamber. The setup allowed us to investigate in detail the effect of different oxidant concentrations and the importance of oxidation time scales on the processing of the particles.