Abstract:
Vehicle soak duration (i.e., ‘parking time’) is closely related to fuel vaporization efficiency and the operating temperature of the three-way catalytic converter (TWC) during restart, thereby influencing tailpipe emissions. To investigate the impact e of soak duration on VOC emissions from gasoline vehicles, this study performed chassis dynamometer- tests on two representative China VI light-duty gasoline vehicles under three soak conditions (t < 0.5 h, 1.5 h < t < 4 h, and t > 6 h). Tailpipe VOCs were sampled and analyzed, and their ozone formation potential (OFP) was calculated using the Maximum Incremental Reactivity (MIR) method. Results showed that as soak duration increased from t < 1.5 h to t > 6 h, the average VOC emission factor increased from 10.9 mg/km to 30.6 mg/km, and the OFP rose from 26.1 mgO
3/km to 109.4 mgO
3/km. The proportion of highly reactive species such as olefins and aromatics also increased significantly. When soak duration exceeded 1.5 h, VOCs emitted during the first 589 s (start-up phase) accounted for over 75% of total emissions in the 1800 s test cycle, and contributed more than 85% of the total OFP. It is recommended to develop a refined VOC emission inventory that incorporates soak duration parameters based on typical vehicle usage patterns in China, and to promote emission control technologies for cold-start conditions following long soak periods.