A method for determining carbonyl emissions from motor vehicles was developed in which exhaust gases from test vehicles running on a dynamometer are directly collected in 6-L Teflon bags and then introduced into pentafluorophenyl hydrazine -coated adsorbent tubes for derivatisation and subsequent analysis of generated derivatives by GC/MS. Twenty gasoline and LPG light-duty vehicles were sampled at a vehicle inspection station in Guangzhou, China, by running test vehicles over a transient testing cycle and analysed for carbonyls. Results show that the method can achieve a detection limit of 8-28 ng m −3 for individual carbonyls with a relative standard deviation of 14.5%. Twenty-four carbonyls were identified in the gasoline vehicle exhaust gases and their total concentration was 19.2 mg m −3 . For the LPG vehicles, 20 carbonyls were found in the exhaust gases with a total concentration of 4.71 mg m −3 . Based on the results, carbonyl emission factors for the gasoline and LPG vehicles were estimated to be 25.0 and 7.36 mg km −1 , respectively.