Statistical analysis of the vehicle pollutant emissions derived from several European road tunnel studies

Real-world emission rates of road traffic can be quantified by measurements in road tunnels. Emission factors (EFs) of in-use vehicles can be determined and the impact of major changes in technology and fuel composition can be estimated. Here, we present tunnel measurements of nitrogen oxides (NOx), carbon monoxide (CO), and total volatile organic compounds (t-VOCs) performed in spring 2001 in the Lundby tunnel (Sweden), in fall 2001 in the Plabutsch tunnel (Austria) and in fall 2002 in the Gubrist tunnel (Switzerland). In this paper, we derive EFs for light and heavy duty vehicles (LDVs and HDVs) by the statistical method of linear and non-linear regression analysis. The results demonstrate the large effect of the tunnel road gradient for NOx emissions of HDVs, whereas the influence of the road gradient is less pronounced for LDV emissions of NOx and CO. The developed statistical modeling approach allows the determination of EFs as a function of vehicle speed. The results also indicate a dependence of the EFs on the day of the week, probably caused by differences in the fleet composition.