Speciated volatile organic compounds and hydroxyl radical reactivity characteristics of evaporation emissions from China VI and China V in-use light-duty gasoline vehicles

Abstract. Vehicle evaporation emission is one of the important sources of volatile organic compounds (VOCs) in the atmosphere. Research on its emission factors and chemical composition, especially the emissions from in-use vehicles under the new regulatory standards, is still scarce and affects the understanding of evaporation emissions. In this work, evaporative emission measurement for in-use gasoline vehicles was carried out for the China VI and China V vehicles, and their emission factors, chemical compositions and hydroxyl radical total reactivity (kOH) were measured. These three evaporative emission processes, hot soak loss (HSL), diurnal breathing loss (DBL) 24 h, and DBL 48 h emission factors, China V vehicles can reach 3.2, 4.6 and 7.6 times that of China VI vehicles, and high mileage vehicle aging and abnormal evaporative emission control systems can significantly increase emissions. In the HSL process, aromatics dominate, with contributions from China VI and China V reaching 44.1 % and 42.8 %, followed by light carbon alkanes (LC-alkanes, ≤ C6). In the DBL process, the chemical components were dominated by LC-alkanes, contributing 40.7 %–50.5 %. The source profiles of evaporative emissions have been established, with n-butane (3.2 %–26.1 %), isopentane (6.2 %–13.5 %), toluene (6.1 %– 16.0 %) being the more important components. It was also discovered that n-pentane/ethane and methyl tert-butyl ether/benzene with can be used to discriminate the sources of evaporative emissions and exhaust. The kOH analysis revealed that branched chain alkenes (BC-alkenes), linear alkenes and aromatics were the most reactive components, such as mainly 2-methyl-2-butene, 2-methyl-1-butene, trans-2-pentene and toluene etc. The measurement of BC-alkenes has expanded our understanding of highly reactive components. It is necessary to strengthen the measurement of high reactivity alkenes, especially BC-alkenes, in future research.