The importance of periodic vehicle emission tests for air quality

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European legislation has a very good instrument to detect high emitting vehicles in use – the periodic emission test of vehicles. It should identify failures or manipulation of emission systems and force the owner of the vehicle into repair or maintenance work. Unfortunately the currents periodic emission test is not applicable any more for modern diesel and patrol vehicles.

Why? The current test procedure was developed over 25 years ago and only slightly adopted to the development of modern vehicles. This means e. g. that a EURO 5 diesel vehicle would pass the periodic emission test even if the particular trap is removed and the smoke emission increase by 500 times. In addition, important pollutants like NOx cannot be measured at all.

The consequences are that manipulation or even normal deterioration of the emission systems cannot be detected during the periodic emission test. This again means that millions of vehicles in Europe are so called gross polluter with a dramatic negative impact on air quality. The EC estimates that only 5 % of these vehicles are responsible for minimum 25% of all the emissions caused by vehicles with combustion engine. If we would be able to detect the gross polluting vehicles with a modern emission test we could reduce the emissions dramatically.

There’s an urgent need to modernize the periodic emission test. The European wide CITA SET I study shows that on a short term perspective it would be very helpful to introduce a mandatory tail pipe test and OBD reading in combination with more stringent thresholds. This could be implemented with the current test procedures and the equipment. Germany e. g. is going this way starting this year.

The kind and the amount of pollutants of new vehicles changed a lot over the last years. I just want to give two examples: The size of particulate matters (PM) of diesel vehicles is becoming smaller and smaller and a high efficient engine, e.g. EURO 6 is producing much more NOx than a EURO 4 engine. Therefore very effective but also expensive after treatment systems are necessary to clean the emissions of modern vehicles. On the other hand petrol direct injecting vehicles are emitting PM like diesel vehicles which makes a particulate emission test also for petrol vehicles meaningful.

First studies show that for a proper evaluation, especially of NOx emissions, a simple loaded test in combination with a comprehensive and standardized OBD reading is very promising. If we want to keep the emission standard of modern vehicles on a high level during the whole life cycle then we need a modernized periodic emission test. As long as defects or manipulation are not detected nobody would repair it.

This new approach for an emission test  doesn’t automatically increase costs for the car owner. Even if the measurement equipment would become more costly, the more expensive part of an emission test is the working time of the inspector. If the test could be conducted faster than today, you could compensate additional costs for the equipment. If we really want to improve air quality in urban areas where still for many years the combustion engine will be the most widespread propulsion, we need to conduct proper and valid emission tests.

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