Quantification of temperature dependence of vehicle evaporative volatile organic compound emissions from different fuel types in China.

ABSTRACT

The evaporative emissions of volatile organic compounds (VOCs) from motor vehicles are dependent upon the ambient temperature. However, the quantitative relationship between evaporative VOC emissions and ambient temperature has rarely been reported, and it is not reflected in the Chinese VOCs emission inventory (EI). In this study, a series of evaporative tests were conducted on a parked gasoline-fueled vehicle in a Variable Temperature Sealed Housing Evaporative Determination chamber under seven temperatures from 298 K to 313 K at intervals of 2.5 K. Results showed that total hydrocarbon emissions at 313 K were 25.7, 12.3, and 26.7 times those at 298 K for China V, China VI, and ethanol-blended E10 fuels, respectively. China V consistently exhibited the lowest evaporative VOC emissions at all temperatures, while those of E10 surpassed even those of China VI and became the highest at 308 K and higher. Along with increasing temperature, the proportions of alkanes and alkenes gradually increased whereas those of aromatics and oxygenated VOCs decreased. Alkenes accounted for less than 20% of the evaporative VOC emissions but contributed to approximately 60% of the total OH loss (LOH) at 298 K and to over 70% at 313 K. cis-2-Butene and trans-2-butene were responsible for the greatest increase in LOH from China V, due to their higher OH reactivity. Our results clearly demonstrated the exponential increases of evaporative VOC emissions and the associated atmospheric reactivity with temperature, and also highlighted that upgrading the emission standard from China V to China IV and promoting the E10 fuel would not contribute to the reduction of evaporative VOC emissions. The strong temperature dependence of evaporative VOC emissions underscores the importance of developing a temperature-driven dynamic EI in China, and the functional relationships retrieved from this study form an essential step in developing such a dynamic EI.