Real-world VOCs from ethanol gasoline vehicles: Speciation, ozone formation potential, and inter-city differences

Ethanol-blended gasoline is increasingly deployed to decarbonize transport, yet its real-world impacts on vehicular volatile organic compound (VOC) speciation and ozone/secondary aerosol formation remain uncertain. We combined on-road exhaust measurements from six light-duty ethanol gasoline vehicles (EGVs), equipped with gasoline direct injection engines and fueled with commercial China VI-B E10, with tunnel and urban observations in China. We quantified 108 VOC species and evaluated their associated ozone formation potential (OFP) and secondary organic aerosol formation potentials (SOAFP). As emission standards tightened from China V to China VI-a, ∑VOC emissions declined substantially from 1290 ± 270 to 686 ± 154 mg/kg-fuel, with higher driving speeds further lowing ∑VOC. Relative to pre-generation VI-A E10, the VI-B fuel reshaped speciation more than it reduced total emissions: oxygenated VOCs (OVOCs) increased by ∼40 %, while alkenes+aromatics decrease by ∼26 %, yielding an order-of-magnitude reduction in ≥C₆ BTEX. Unburned ethanol was the defining species (472 ± 113 mg/kg-fuel; 46 ± 11 % of ∑VOC) and the largest single contributor to OFP (∑OFP 1590 ± 264 mg O₃/kg-fuel), shifting OFP composition toward OVOC dominance (53-58 %). Inter-city contrasts in mixing and emission ratios (mandatory > adjacent > distant regions; R² = 0.61-0.71 between tunnel and urban sites) indicate that mandated E10 use elevates ambient ethanol and acetaldehyde and modifies downwind precursor mixtures, with potential implications for regional ozone and other secondary pollutants. These findings provide critical constraints for improving emission inventories and regional air-quality models, underscoring the potential for EGVs to influence air quality over broader spatial scales.