Characteristics of volatile organic compounds from vehicle emissions through on-road test in Wuhan, China.

VOCs emissions from motor vehicles have become a main source of air pollution in many cities. However, the characteristics of VOCs emissions have not been fully elucidated. Ten representative vehicles were selected in Wuhan, China, and the VOCs emitted by these vehicles under actual working conditions were collected and analyzed through on-road tests. Results showed that the average concentrations of total VOCs emitted by gasoline and diesel vehicles were 5.9 ± 2.4 mg/m and 6.8 ± 3.0 mg/m, while the average emission factors were 5.3 ± 2.2 mg/km and 33.9 ± 22.7 mg/km, respectively. The five compounds emitted at the highest levels by gasoline and diesel vehicles were hexanal, acetone, toluene, p-xylene and iso-pentane. Emission concentration of diesel vehicles was slightly higher than that of gasoline vehicles. Emission factor of diesel vehicles was much higher, because they consumed more fuel and produced more power than gasoline vehicles. The average concentrations of total VOCs emitted by China III, IV and V vehicles were 8.4 ± 1.4 mg/m, 5.8 ± 3.4 mg/m and 5.3 ± 1.9 mg/m, and their average emission factors were 21.7 ± 18.6 mg/km, 19.4 ± 28.9 mg/km and 9.1 ± 7.2 mg/km, respectively. Vehicle emissions decreased obviously as the emission standards increased. The average concentrations of total VOCs emitted under low-speed and high-speed conditions were 9.4 ± 3.5 mg/m and 5.5 ± 1.8 mg/m. Concentrations of acetone, hexanal, toluene and p-xylene were the highest four VOCs under both conditions. The average emission factor of VOCs under high-speed conditions (24.0 ± 13.6 mg/km) was substantially lower than under low-speed conditions (54.0 ± 41.5 mg/km). Thus, tightening emission standards and reducing traffic congestion would help reduce VOCs emissions.