On-Road Evaporation Emissions: An Important Contributor to Ozone Pollution

Tropospheric ozone has become a major air quality concern, with nonmethane volatile organic compounds (NMVOCs) as key precursors. Previous on-road emission studies suggest on-road evaporation emissions now rival or exceed exhaust emissions as NMVOC sources in urban areas, driving increased regulatory attention. However, the effectiveness of evaporation emission control in mitigating ambient ozone remains poorly quantified. Using chemical transport model simulations over eastern China during summer 2017, we investigate regional ozone responses to 100% reductions in on-road evaporation NMVOC emissions. Results reveal pronounced regional variation in O 3 benefit tied to local photochemical regimes. In VOC-limited regions (Beijing–Tianjin–Hebei and the Yangtze River Delta), evaporation emission controls reduce maximum daily 8-h average ozone (MDA8h O 3 ) by up to 8 ppbv, equivalent to a 10% relative decrease. In contrast, non-VOC-limited regions exhibit minimal response (<1 ppbv), indicating negligible O 3 health benefits from evaporation controls alone. These findings demonstrate that uniform national evaporation emission standards may raise regional health inequality in ozone benefits. We recommend prioritizing evaporation emission regulations in these regions while pursuing concurrent NO x -VOC cocontrol strategies in transitional and NO x -limited areas to maximize ozone mitigation effectiveness.