Dynamic Chemical Exposure from Face Masks Induced by Ambient Ozone Oxidation Chemistry

The widespread use of face masks on a global scale calls for a comprehensive evaluation of the associated chemical exposure. However, researchers mainly focus on the chemicals directly emitted from masks, with no consideration given to their possible transformation chemistry and the associated potential health impacts during the use of masks. Here, via mask wearing experiments (by volunteers), ambient air-mask interaction experiments, and ozone-mask reaction experiments, we find that the chemical exposure will be substantially changed during mask wearing due to gas-mask multiphase reactions with ambient ozone. In particular, this ozone oxidation chemistry leads to the formation of gaseous carbonyl compounds and a surface-bound organophosphate ester tris(2,4-di-tert-butylphenyl) phosphate (TDtBPP, an emerging contaminant), with concentrations up to five times higher than those present in unused masks. While exposure assessments indicate that the health risks posed by gaseous carbonyl compounds and surface-bound organophosphate esters are likely to be minor, the present work emphasizes the importance of considering the dynamic evolution of mask-related chemicals when evaluating the overall chemical exposure related to face mask usage.