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 PM_2.5 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.