Abstract
At two monitoring points established inside the Xi'an urban road tunnel, China, measurements of concentrations of the pollutants from motor vehicles, observations of meteorological conditions in the tunnel, and counting and classification of vehicles passing through the tunnel were conducted. The emission factors of CO, HC, and NOx from the motor vehicles on urban main road in China were 33.279±12.158, 3.577±1.816, and 4.605±1.981mg/(m.veh), respectively, which were derived from the mass balance equation based on the measured data. In comparison with the emission factors in the developed countries, the CO, HC and NOX emission factors of the vehicles on urban main road in china are nearly 7-8 times, 8-10 times and 3-4 times, respectively.