Evaporative emission from China 5 and China 6 gasoline vehicles: Emission factors, profiles and future perspective

Vehicular evaporative emission is a major source of atmospheric volatile organic compounds (VOCs), while quantification and characterization of the evaporative emission in China, particularly for the vehicles meeting the latest emission standards, are rarely reported. In this study, we performed evaporative emission experiments in a sealed housing evaporative determination (SHED) using eleven new and in-use light-duty gasoline vehicles to investigate the evaporative VOCs emission from the China 5 and China 6 vehicles and unravel the deterioration of evaporation control system of in-use ones. The total hydrocarbon (THC) emission factors (EFs) of 24-h diurnal breathing loss from the new China 6, new China 5 and in-use China 5 vehicles are 0.25, 0.81 and 5.27 g/d respectively. Compared with headspace vapor, the emission profiles of both hot soak loss (HSL) and diurnal breathing loss (DBL) from all new tested vehicles contain more C7–C9 aromatics, particularly for the China 6 vehicles. C4–C5 alkanes and C7–C9 aromatics account for most of total VOCs mass for all China 5 vehicles, while emissions from the China 6 vehicles exhibit no strongly prevailing species for both HSL and DBL emission. Typical ratios like normalized ratios of benzene, toluene and ethylbenzene can be used to distinguish evaporative emission from vehicular exhaust. Ozone formation potentials (OFPs) of the in-use China 5 vehicles are 5.35 and 7.16 times higher than that of China 5 new ones in DBL and HSL experiments respectively. Secondary organic aerosol formation potential of all tests ranged from 17.30 to 29.76, with aromatics contributing the largest proportion (over 90.0%). With the implementation of China 6's standard, the evaporative THC emission in China may peak in 2022 and will be cut down by 76% until 2030. Also, the underestimation of evaporative emission was estimated when neglecting the difference of EFs between new and in-use vehicles.