Liquid fuel intrusion causes carbon canister deterioration and excess evaporative VOC emissions from in-use vehicles.

Vehicular evaporative emissions are major sources of urban volatile organic compounds (VOCs), significantly contributing to secondary organic aerosols (SOA) and ozone (O3) formation. While most research has centered on characterizing fundamental emissions profiles, the mechanisms and quantification of high-emitters remain unexplored. Here, an investigation involving full-process evaporative emission testing of hot soak, diurnal, refueling and running loss was conducted on 11 in-use vehicles. A critical anomaly revealed that all high-emitters exhibited fuel intrusion within the carbon canister (the core control device for evaporative emissions), elevating emission levels 3-9 times above normal vehicles, with VOC profiles resembling fresh fuel vapor. Furthermore, we integrated experiments-including six-degree-of-freedom (6-DOF) motion simulation, emission tests and carbon characterization. Results showed that 0.5 h of driving could induce up to 16 mL of fuel intrusion, with 100 mL cumulative intrusion disabling the canister. Fuel intrusion is primarily triggered by vehicles driving on slopes, curves or rough roads. The intruded fuel blocked key activated carbon pores (0.5-1.6 nm and 2-3 nm), reducing pore volume by 11.5% and 9.1%, respectively, and irreversibly deteriorating adsorption capacity. Inventory results indicate that fuel intrusion vehicles accounted for 51.2% of evaporative emissions in Tianjin. Combining field and lab studies confirms that fuel intrusion-an overlooked mechanism-significantly increases evaporative emissions from in-use vehicles, highlighting the need for stricter regulatory oversight.