The primary tool for combating air pollution from road transport is vehicle emission legislation. There are currently two main levels of emission legislation: type approval, and periodic in-service/roadworthiness technical inspection.
Emission tests are normally required for the type approval of all new passenger car (M1, M2) and light-duty vehicles (N1, N2), and for the engines used in heavy-duty vehicles. Emission limits have been applied to vehicles and engines at the type approval stage since the early 1970s. The exhaust pollutants which are regulated are CO, unburnt hydrocarbons (HC), NOx and PM. The limits have been reduced in stages since they were first introduced (through progressive ‘Euro’ standards), and changes have been made to the test methods to make them more realistic and effective.
Emission-control technologies have developed accordingly.
For cars and light-duty vehicles the test procedures and limit values have been consolidated in the Euro 5 and Euro 6 legislation (Regulation (EC) No. 692/2008). In the exhaust emission test a production vehicle is placed on a power-absorbing chassis dynamometer. The driver must follow a driving cycle and the vehicle’s emissions are collected and analysed. Emissions are measured over the New European Driving Cycle (NEDC), which is composed of low-speed ‘urban’ segments and one high-speed ‘extra-urban’ segment. The vehicle exhaust gases are diluted with filtered air to prevent condensation or reaction between the exhaust gas components.
Dedicated analysers are used for CO, NOx, HC and carbon dioxide8. For diesel vehicles up to and including Euro 4, PM was collected separately from the other pollutants on a filter. For Euro 5 and Euro 6 vehicles PM mass and PN are measured using the new Particulate Measurement procedure. The PN limit is designed to prevent the possibility of the PM mass limit being met using technologies that would enable a high number of ultrafine particles (<0.1 μm diameter) to pass.