On-road emissions of fine particles and associated chemical components from motor vehicles in Wuhan, China

Vehicle emission is an important contributor to urban air pollution with the increasing number of motor vehicles. Ten typical vehicles were selected in Wuhan to study the emissions of fine particular matters (PM2.5) and associated chemical components by on-road tests through a Portable Emission Monitoring System (PEMS). The emission factors of PM2.5 and the compositions of it from different types of vehicle were obtained. Results showed that the average emission factors of PM2.5 from gasoline and diesel vehicles were 1.266 and 16.589 mg/km. As the emission standard of vehicles increased from China III to China V, PM2.5 emission factor gradually decreased from 17.385 to 1.520 mg/km. Emission rate of PM2.5 was 0.0384 mg/s under low speed, and it increased to 0.0775 and 0.0964 mg/s under the medium and high speeds. The ratio of organic carbon versus elemental carbon (OC/EC) in PM2.5 from gasoline vehicles was 6.89, which was greater than that of diesel vehicles as 3.12. Because gasoline was made of small molecules and the compression ratio of gasoline engine was relatively low, some OC remained in the area where the ignition failed in the cylinder. The top four water-soluble ions with high emission factors were Cl-, SO42-, Ca2+, and Na+, while K, Na, Ca and Mg had a larger emission factors in the 21 tested inorganic elements. These water-soluble ions and inorganic elements mainly came from the oil burning, fuel additives and engines wear. Results of PM2.5 emission characteristics would help to improve the air quality in Wuhan.