Assessment of alternative fuels for on-road volatile organic compounds emission characteristics: Ethanol-containing gasoline and natural gas

Despite the growing popularity of alternative fuels, their impact on exhaust emissions, particularly those of speciated volatile organic compounds (VOCs), remains insufficiently recognized. Herein, the impacts of alternative fuels (including ethanol-containing gasoline and compressed natural gas) on regulated gaseous and VOC emissions were compared to those of conventional gasoline. One private car and one bi-fuel taxi were tested based on portable emission measurement systems in the Real Drive Emission testing, representing real on-road driving conditions. Although an adverse effect of compressed natural gas on NOx emissions was found, alternative fuels could effectively reduce other regulated gases and VOC emissions. With the decrease in VOC emission factors for alternative fuels, VOC reactivity and ozone formation potential showed more significant decreases than VOC emission factors, demonstrating favorable environmental implications for alternative fuels. A greater proportion of OVOC species, which are closely related to urban air pollution and persistent pollutant formation, was observed in the exhaust gases of alternative fuels, showing that OVOC control cannot be neglected once alternative fuels become widespread. These results facilitate an understanding of the environmental benefits of replacing gasoline with alternative fuels in light-duty vehicles. It will be further beneficial to future engine optimizations and advanced emission control technologies and provide environmental-based guidance on the utilization of alternative fuels.