On-road measurements of NMVOCs and NOx: Determination of light-duty vehicles emission factors from tunnel studies in Brussels city center

The emission factor of NOx is (544 ± 199) mg vehicle−1 km−1; NMVOCs emission factors vary from (0.26 ± 0.09) mg vehicle−1 km−1 for cis-but-2-ene to (8.11 ± 2.71) mg vehicle−1 km−1 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.