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Diesel cars slammed in new pollution test

Diesel cars have been slammed in a new pollution test showing that nitrogen oxide (NOX) emissions exceed the laboratory results in real-world testing.

THE INTERNATIONAL Council on Clean Transportation claims there’s a wide discrepancy between official certification of nitrogen oxide (NOx) levels and actual NOX emissions in real-world use, in a new report. The ICCT report focussed on NOx due to the affect it can have on respiratory health, claiming its testing of 15 diesel cars revealed that real-world NOx emissions were up to seven times higher than the official figure.

The report stated, “Ambient NOx concentrations in Europe regularly exceed current EU air quality standards (200 µg/m3 one-hour average for nitrogen dioxide, 40 µg/m3 one-year average), especially in urban areas. And Europe’s transport sector is the single largest contributor (about 40%) to total ambient NOx concentrations”.

“Standards regulating NOx and other exhaust emissions from passenger cars in the EU have become more stringent over time: The permissible limit for emissions of nitrogen oxides (NOx) from diesel cars declined from 500 milligrams per kilometer (mg/km) under Euro 3 (effective January 2000) to 80 mg/km under Euro 6 (effective September 2014).”

New cars are certified as meeting the required standards via a laboratory test, but the ICCT reports those test results aren’t accurate.

The ICCT report looked at the on-road emissions performance of 15 new diesel cars, 12 certified to the Euro 6 standard and three to the US equivalent (Tier 2 Bin 5), using portable emissions measurement systems (PEMS), which provide a continuous stream of vehicle data signals including emission rates, velocity, acceleration, road gradient and exhaust temperature.

According to the ICCT, “Emissions were measured over 97 trips, totaling more than 140 hours of operation and 6400km driven. The high temporal and spatial resolution of PEMS datasets permitted the analysis to link elevated NOx mass emission rates to the driving conditions that caused them.

“This is the first systematic analysis of the real-world performance of modern diesel passenger cars, and the most comprehensive profile available of the on-road behaviour of the latest generation of diesel passenger cars”.

ICCT testing revealed that real-world NOx emissions from the tested vehicles were a staggering seven times higher than the official limit set by Euro 6. “If applied to the entire new vehicle fleet, this would correspond to an on-road level of about 560 mg/km of NOx (compared to the regulatory limit under Euro 6 of 80 mg/km),” the ICCT reported.

One criticism of such tests is that the spiked results are often caused by ‘extreme’ driving, but the ICCT said that wasn’t the case with its results. It said, “Instead, they were due to transient increases in engine load typical of everyday driving (e.g., going up a slight incline), or to normal regeneration events in the normal diesel exhaust after-treatment systems.

But it wasn’t all doom and gloom, “Performance differences among the vehicles tested indicate that the technologies for real-world clean diesels already exist. Some of the tested vehicles had average emissions below Euro 6 emission limits, suggesting that the technologies to achieve that level of performance are available, but that policies are not yet in place that can force manufacturers use these technologies and calibrate them to effectively control emissions over the majority of in-use operating conditions, not just those covered by the test cycle.”

The ICCT is calling on the European Commission to introduce on-road pollution testing for the passenger-car type-approval process in the EU.


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Isaac Bober

Isaac Bober