Institute for Transport Studies (ITS)

Remote Sensing Vehicle Emissions

The ITS Vehicle Emission Measurement System (VEMS) senses the tailpipe emissions of vehicles as they drive-through a monitoring site. The instrument scans the exhaust plume trailing a vehicle. This approach is commonly used in the U.S. and Canada in large-scale emission testing programs. Manufactured by ESP Global, the ITS AccuScan 4600 instrument when installed at a good test-site is able to measure ratios of NO, CO, HC, Particles to CO2 i.e. fuel-based emission factors.

VEMS

The Vehicle Registration Mark (VRM with ANPR), speed and acceleration are also recorded. Coupling these emission measurements with detailed vehicle registration information (DVLA records) such as Euro standard, fuel type, engine size, weight etc, provides a rare opportunity to:

  • Study the composition of the vehicle fleet being driven on the road. This is important as for example, modern diesel passenger cars are now understood to be one of the main contributors towards the increase in primary NO2emissions. As they also complete many more miles per year than comparable petrol cars, it is becoming necessary to maintain an accurate and up-to-date knowledge of their proportions on the road; and
  • Study the on-road emission characteristics for each vehicle/ fuel type/ Euro standard sub-category. Whilst VEMS is not currently able to measure nitrogen dioxide (NO2) directly, with knowledge of a vehicles’ fuel type, Euro standard, nitrogen oxide emissions and recommended tail-pipe NO2 fraction, its NOX and NO2 contribution can be predicted.
VEMS - Predicted N02(%)/C02(%) ratios

Analysis of passenger car measurements from October 2009 and July 2010, supported by Calderdale MBC, has shown that whilst emission ratios for petrol cars are falling broadly in-line with each successive and more stringent Euro standard, NO and predicted NOX emissions from diesel cars show little sign of decline. The surge in vehicle miles driven by modern diesel vehicles is also predicted to contribute increasing amounts of NO2 from the tail-pipe. These findings are in-line with other work, that highlight an unwanted side-effect of new diesel engine emission abatement technologies is an increase in tail-pipe NO2emissions. As there’s little forecast improvement in the NO2 emission characteristics of diesel cars yet to be introduced (e.g. Euro 6), it is considered there’ll be little improvement/ a worsening of roadside NO2 concentrations at heavily trafficked UK and EU locations. Without a radical shift in direction, EU and UK NO2 limit values are likely to continue to be exceeded at the most polluted roadside sites.

This new approach, combining on-road VEMS measurements with detailed vehicle registration information offers an opportunity to extend and maintain an up-to-date evidence base, and contribute to the development of more targeted and effective management strategies. Researchers and Authorities interested in better understanding on-road vehicle emissions are encouraged to contact Dr James Tate.

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