Emission factors (EFs) of pollutants emitted by light-duty vehicles (LDV) were investigated in the Leopold II tunnel in Brussels city center (Belgium), in September 2011 and in January 2013, respectively. Two sampling sites were housing the instruments for the measurements of a large range of air pollutants, including non-methane volatile organic compounds (NMVOCs), nitrogen oxides (NO x) and carbon dioxide (CO 2). The NMVOCs and NO x traffic EFs for LDV were determined from their correlation with CO 2 using a single point analysis method. The emission factor of NO x is (544 ± 199) mg vehicle À1 km À1 ; NMVOCs emission factors vary from (0.26 ± 0.09) mg vehicle À1 km À1 for cis-but-2-ene to (8.11 ± 2.71) mg vehicle À1 km À1 for toluene. Good agreement is observed between the EFs determined in the Leopold II tunnel and the most recent EFs determined in another European roadway tunnel in 2004, with only a slight decrease of the EFs during the last decade. An historical perspective is provided and the observed trend in the NMVOCs emission factors reflect changes in the car fleet composition, the fuels and/or the engine technology that have occurred within the last three decades in Europe.