In order to study the characteristics of major pollutants emitted by motor vehicles, a tunnel test was carried out in a representative tunnel in downtown Xi'an. Through continuous online monitoring at both entrance and exit of the tunnel, meteorological data, traffic parameters and mass concentration data of PM_2.5, CO, NO_x, HC and VOCs were obtained. By calculating the emission factors of motor vehicles, it was found that the average emission factors of PM_2.5, CO, NO_x, HC and VOCs were (0.016±0.005), (1.097± 0.398), (0.159±0.092), (0.179±0.089) and (0.317±0.172) g/(km·veh), respectively. The emission factors varied with time during the day, and the emission factors of PM_2.5 were obviously smaller than gaseous pollutants. In addition, the emission factors declined dramatically as compared to the previous study in China, which might owe to the improvement of fuel quality, engine efficiency, exhaust control technology and urban management.

tunnel test  /  pollutants emitted by motor vehicles  /  emission factors