Evaporative emission characteristics of VOCs from in-use light-duty gasoline vehicles

VOCs are an important precursor pollutant of ozone (O3) and secondary organic aerosols (SOA). Vehicle evaporative emission is an essential source of VOCs in urban area, among which lack of localized tests of running loss process in China. This study tested all the evaporative emission processes of in-use light-duty gasoline vehicles (LDGVs), including refueling, running loss, hot soak, and 48-h diurnal breathing loss (DBL) based on the variable temperature Sealed Housing for Evaporative Determination (VT-SHED) of REU (China 4, China 5) vehicles and REC (China 6, with Onboard Refueling Vapor Recovery system) vehicles. The emission factors (EFs), species profiles, Ozone formation potential (OFP), and SOA formation potential (SOAP) of all evaporative emission processes of REU and REC vehicles were obtained. We found that the running loss emissions was less affected by the Onboard Refueling Vapor Recovery (ORVR) system, the average running loss EFs of REU and REC vehicles was 9.386 mg/km; refueling and DBL EFs of REC vehicles was 1.491 mg/L and 0.179 g/day, respectively, 99.8% and 56.0% lower than those of REU vehicles, the hot soak EFs was 0.087 g/h in average. The refueling emissions process was dominated by alkanes (REU: 77.8%; REC: 75.4%), and C4 and C5 species dominated (REU: 75.6%; REC: 67.6%). Among the running loss, hot soak and DBL emissions, alkanes, oxygenated VOCs (OVOCs) and aromatics were the dominant VOCs groups, OVOCs account for a higher proportion in REC vehicles than in REU vehicles. REC vehicles had higher proportion of C1-C3 than REU vehicles, it may be that ORVR has a better adsorption effect on species with large carbon numbers. Running loss VOCs species had a strong correlation with hot soak VOCs species. The OFP of running loss in REU and REC vehicles were 0.9-1.3 and 0.3-0.7 times higher than those of refueling and 48-h DBL, while the SOAP were 10.7-12.9 and both 1.1 times higher, respectively. These findings can provide valuable basis for emission estimation and characteristic analysis for evaporative process of LDGVs and support the development of appropriate pollution-control policy.