Study On Emission Factors Of NOx And CO From Vehicles By Using The Inverse Model Method

Emission factors are defined as the mass or number of an air pollutant emitted by a vehicle when it traveled unit distance or unit mass of fuel used. Emission factors are the basic parameters not only in indicating vehicle pollutant emissions and estimating vehicle emission share in urban atmospheric pollutants, but also in employing and evaluating various control technologies on vehicle emissions. The objective of this paper is to determine the NOx and CO emission factors for the average vehicle fleet by using the inverse modeling method, and to estimate the NOx and CO emission factors for light-duty vehicles (LDV) and heavy-duty vehicles (HDV) by using the multiple regression method, on the basis of analyzing the characteristic of the NOx and CO concentrations and traffic flow in an urban street canyon. The results of the study can provide the reference parameters for evaluating the emission pollution of vehicles in city and the impact of vehicles exhaust pollutants on human health.The data used in this paper were observed at an environmental air quality monitoring station inside HG canyon Street and at a background monitoring station inside RG Street. The distance between RG Street and HG Street monitoring sites is 600 meters. The data used in this study are selected from June 1,2002 to January 31,2003, because the data in this period are continuous. The hourly-mean time series values include NOx and CO concentrations, traffic flow and meteorological parameters such as wind speed and wind direction etc.The NOx and CO average emission factors for the vehicle fleet are 2.809±0.026, 12.162±0.132g/(km-veh), respectively. The NOx emission factors for LDV and HDV are 2.448±0.129,12.588±3.430g/(km-veh), respectively. For CO, the emission factors for LDV and HDV are 15.621±0.659,73.083±17.504g/(km-veh), respectively. The statistical analyses show that the correlation coefficients (R) of the emission intensity of NOx and CO with traffic flow are 0.885 and 0.850, respectively.The estimated emission factors of NOx and CO in this study are compared with other published values. The comparison shows that the NOx and CO average emission factors for the vehicle fleet, the NOx emission factors for LDV and HDV and the CO emission factors for LDV in this study are all the same order of magnitude with other published findings, but the CO emission factors for LDV is significantly higher than the values from some comparable studies.