Gerrit Kadijk BSc
- emission factors
Clean air is vital to health. Air quality can be improved by cutting road-vehicle emissions. TNO has been commissioned by the Ministry of Infrastructure and the Environment to conduct an In-Service Conformity programme for passenger cars, to obtain a better understanding of their emissions. As part of that programme, TNO is carrying out real-world measurements to gather objective data on passenger-car emissions. The emission of particulate matter is one of the programme’s focus areas.
The combustion of diesel fuel in a vehicle’s engine produces particulates, which are often referred to as ‘particulate matter’ or ‘PM’. These particulates are emitted to the environment through the exhaust. Particulates have a negative impact on human health, because they enter the human body through the lungs.
To reduce the emissions of particulate matter, modern diesel passenger cars and vans are fitted with a closed diesel particulate filter (DPF). In everyday practice, the introduction of diesel particulate filters has cut particulate emissions from these road vehicles by 95% to 99%.
However, particulate filters are sometimes removed, for various reasons, and this has a major adverse impact on air quality. Thus, it is important to ensure that particulate filters remain in place throughout the operational life of the vehicle, and that they continue to function properly.
In the current MOT, the Periodic Technical Inspection for passenger cars and vans, the emissions of modern diesel vehicles fitted with particulate filters are checked by retrieving data from the On-Board Diagnostics (OBD) system. However, when the particulate filter is physically removed, the vehicle’s software is also modified in order to prevent fault codes from occurring. For this reason, the OBD check will not show whether the particulate filter has been removed.
Older diesel vehicles (up to and including Euro 4) are subjected to a smoke measurement. Such measurements have been used for many decades. Only those cars that produce very high emissions fail this test. Modern diesel vehicles (Euro 5 and Euro 6), fitted with a DPF, undergo a smoke measurement if they fail the OBD test. However, they can easily meet the outdated, high limits for smoke emissions, even without a particulate filter. For this reason, in the current MOT, it is not possible to determine whether or not the particulate filter has been removed.
The report entitled ‘Diesel particulate filters for light-duty vehicles: operation, maintenance, repair, and inspection’, at the bottom of this page, describes, in accessible terms, the most important aspects of particle filters. It also gives details of the options for checking them in the MOT, to see whether they are performing properly.
This report is mainly based on four studies commissioned by the Ministry of Infrastructure and the Environment and carried out by TNO. Those studies (the reports of which can also be found on this page) are briefly discussed below.