Unveiling TWC replacement benefits in in-use vehicles from a concentration-reactivity-toxicity perspective.

Vehicular exhaust represents a major anthropogenic source of atmospheric volatile organic compounds (VOCs), which serve as critical precursors for atmospheric ozone and PM2.5 formation, and characterizing its emission profile and associated health risks provides essential scientific basis for establishing effective emission control standards. Given that Three-Way Catalysts (TWC) currently represent an effective technology for controlling conventional pollutants, this study investigates their indirect benefits for VOC emission reduction on high-mileage China V vehicles. Exhaust samples were collected across multiple driving speed segments and start-up temperature conditions to analyze vehicle VOC emission factors, ozone formation potential, and both non-carcinogenic and carcinogenic health risks. Research findings indicate that renewing the TWC can reduce total emissions of VOCs by more than 88%. Notably, replacing aged TWCs eliminates acrolein, reduces benzene, and lowers 1,3-butadiene emissions, while post-replacement priority pollutants shift to xylenes, ethylbenzene, and acetaldehyde. Alkanes warrant mass-based controls, alkenes demand reactivity management, halogenated VOCs require carcinogenic risk regulation, and both OVOCs and aromatics necessitate integrated health-environmental mitigation strategies targeting their distinct toxic mechanisms. This study provides a new perspective on treatment of in-use vehicle aging TWC from the aspects of emissions, environmental impact, and health risks from a single-vehicle case.