The results of this study were consistent with other vehi cle OFP studies. Bermudez et al. (2011a, 2011b) obtained that OFP of diesel passenger cars was 983 mg O3/km and 967–1281 mg O3/km under different conditions. Tsai et al. (2012) showed that OFP of light-duty diesel vehicles was 852 mg O3/km for FTP-75 cycle and 478 mg O3/km for highway cycle. As for gasoline-powered vehicle, it was tested to emitted 37.6 mg/km carbonyls and the OFP was 228 mg O3/km (Ban-Weiss et al., 2008), which was much lower than that of diesel vehicles. However, for NMHCs, Chang et al. (2001) measured that the average emission factor of four gasoline-powered passenger cars was 403 mg/km, and the OFP was estimated up to 1828 mg O3/km. Total OFP of gasoline-powered vehicles exhaust seems higher than that of diesel vehicles, but the large proportion of carbonyls in the OFP of diesel exhaust needs to be concerned.