Cerium Dioxide-Based Scavenging of Environmentally Persistent Free Radicals in Fine Particulate Matter: A Prospective...

Environmental persistent free radicals (EPFRs) are a class of long-lived, redox-active species that persist on fine particulate matter (PM_2.5) surfaces for days to months. Upon inhalation, EPFRs catalyze the generation of hydroxyl radicals through Fenton-like cycling, driving oxidative stress and inflammation at the site of deposition. Current air filtration technology focuses almost exclusively on physical interception of particulate matter, leaving the surface-bound radical activity of captured PM entirely unaddressed. This review advances a testable hypothesis rather than reporting a validated outcome: that cerium dioxide (CeO₂)-based materials, whose Ce³⁺/Ce⁴⁺ redox cycling is well-established as a broad-spectrum antioxidant mechanism in biomedical contexts, can be functionally migrated to air filtration to chemically quench EPFRs on captured PM_2.5. We first summarize the formation and health impacts of EPFRs, then introduce the mechanistic basis of CeO₂ radical scavenging, emphasizing its self-regenerating valence cycling. We then examine the existing but functionally distinct use of CeO₂ in air pollution control, including its role as an oxygen storage component in three-way catalysis and as an additive in filter media, and argue that these high-temperature oxidation applications do not constitute a functional precedent for ambient-temperature radical scavenging. The central gap is that no study has systematically tested whether CeO₂ can chemically quench EPFRs on PM_2.5 surfaces under filtration conditions. We articulate the key experimental questions that must be resolved-direct EPFR quenching versus ROS interception, the effects of humidity, airflow, and contact time, and the long-term fate of CeO₂ under realistic filtration conditions-and argue that the demonstrated gaseous ROS scavenging of CeO₂ in cigarette smoke, together with its self-recovery capability, provides sufficient mechanistic justification to pursue this direction experimentally.