Science & Environment

Scientists sniff out vehicle emissions

Vehicles Image copyright IUP HEIDLEBERG
Image caption Old and new, motorcycles to buses: A big fraction of NO2 emissions comes from just a few vehicles

German scientists have developed a smart way to investigate the emissions coming out of vehicles on the road.

The Volkswagen scandal underlined the inadequacy of standard lab tests which do not reflect the exhausts produced when driving in the real world.

But the University of Heidelberg team is now getting more reliable data by following behind city cars and buses to "sniff" their tailpipe gases.

Denis Pöhler described the set-up at the European Geosciences Union meeting.

"It's very simple. We've got a small instrument on the back seat of our car. We just suck in the air at the front of our car, taking in this plume from the vehicle in front, and get some values."

GPS tracks the location. A camera identifies the type of vehicle - motorcycle, car, lorry or bus - and the manufacturer.

The team is particularly interested in oxides of nitrogen, which are produced in the combustion process and can be a serious health hazard.

Image copyright IUP HEIDLEBERG
Image caption The Heidelberg chase car: Sampling real driving emissions

For two years, the Heidelberg scientists have been chasing motor vehicles through the streets of a number of Germany towns, with some often quite surprising results.

They have seen a lot of variability in emissions.

Yes, the newest models had, by and large, the cleanest plumes, but this was not always so.

The group would often come across high-polluting vehicles that had been built to comply with the very latest emissions standards (and before you ask: these were not all VWs).

This may indicate faults in the systems installed in these vehicles to clean up tailpipe gases.

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Media captionDenis Pöhler: "We've developed a fast and precise measurement system"

Typically, many of the worst offenders were buses, in particular some older models.

Bizarrely, one of the buses in Mainz producing very high concentrations of nitrogen dioxide was emblazoned with a campaign urging people to get onboard in order to lower emissions.

One clear message, however, does seem to come out of the research: a relatively small number of vehicles on the road is responsible for a high fraction of total emissions.

In the case of Mainz, the plumes of 7.6% of vehicles contained more than 500 parts per billion by volume (about 1,000 microgram per cubic metre) of nitrogen dioxide (NO2). But if you could somehow take just these vehicles off the road, you would reduce emissions by 45%.

"So if you exclude only these high emitters, you have a big impact on air quality," explained Dr Pöhler from Heidelberg's Institute of Environmental Physics.

"If you were to do the same just with old cars, you would have a much smaller impact. It is really important that we focus on the small number of vehicles with very high concentrations."

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