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ICCT: New RDE regulations not enough to control diesel car NOx fully; additional actions required

Real-world NOx emissions from new diesel cars could still exceed the Euro 6 emission limit of 80 mg/km by a factor of three or more, even after the new Real-Driving Emissions (RDE) regulation takes effect, according to a new white paper released by the International Council on Clean Transportation (ICCT). However, taking specific actions beyond those mandated in the regulation—such as introducing spot checks for randomly selected vehicles and expanding the range of driving conditions covered by RDE testing—could reduce new diesel car NOx emissions to 96 mg/km—just 1.2 times the Euro 6 limit—by 2022.

For the study, the team analyzed an extensive set of diesel car emissions data using modeling of the boundary conditions of the RDE regulation. The researchers also examined the impact of ICCT’s proposed modifications.

The authors, Josh Miller and Vicente Franco, modeled real-world emission factors for the Baseline RDE scenario and each progressive RDE+ step using ICCT’s PEMS database of Euro 6 diesel cars combined with expert assumptions on the emissions behavior associated with four types of driving conditions (normal, cold-start, extended driving, and defeat devices/poor calibrations).

Monte Carlo analysis was performed to assess the sensitivity of the modeled emission factors to variations in these input assumptions. The modeled real-world emission factors were combined with EU passenger car stock and activity data and projections up to the year 2030 to forecast the trends in passenger car NOx emissions under various assumptions for RDE and diesel market share. Reference scenarios modeled a relatively constant new diesel car market share; market-shift scenarios examined the sensitivity of results to a decline in diesel market share.

Average real-world NOx emission factors for passenger cars in the EU. Source: The ICCT. Click to enlarge.

Among the findings:

  • Under a Baseline RDE scenario, real-world NOx emissions of new Euro 6 diesel cars will be reduced from 5–7 times the Euro 6 limit of 80 mg/km to 4 times that limit. This multiplier is higher than the regulated conformity factor of 2.1 since it includes real-world emissions resulting from defeat devices, poor calibrations, and driving conditions not covered by the RDE test. Total NOx emissions from passenger cars in the EU-28 are projected to decrease through 2030 as a result of the RDE program and Euro 6 standards.

  • Under a Conservative RDE+ scenario, in which cold-start provisions are added to the RDE test procedure in 2020 and market surveillance and tightened conformity factors are added in 2023, real-world NOx emissions of new Euro 6 diesel cars would be reduced to 2.1 times the Euro 6 limit. If diesel cars retain their current market share, the Conservative RDE+ scenario would reduce NOx emissions from cars in the EU-28 by 210,000 metric tons per year in 2030 compared to the Baseline RDE scenario.

  • In an Accelerated RDE+ scenario, under which the provisions in the Conservative RDE+ scenario are introduced earlier—in 2018 and 2020—followed by a more stringent step in 2022, real-world NOx emissions of new Euro 6 diesel cars would be reduced to 1.2 times the Euro 6 limit. The last, more stringent, step in 2022 would go beyond the current expectations for the RDE, including real-world emissions monitoring via remote sensing, expanded boundaries of the RDE test procedure, and publication of RDE test results to enable independent verification.

Projections of real-world NOx emissions for passenger cars in the EU-28. Source: The ICCT. Click to enlarge.

Since September 2015, all new diesel cars in the EU are required by the Euro 6 standard to meet a NOx emission limit of 80 mg/km. However, investigations in the aftermath of the Volkswagen diesel emissions scandal—for example by the German type-approval agency KBA—have confirmed that the majority of current vehicles meet the Euro 6 NOx limit only during laboratory testing. On-road emissions are much higher—about 5–7 times the Euro 6 limit (400–560 mg/km), on average.

Beginning in September 2017, the Real-Driving Emissions (RDE) regulation will require that diesel cars also undergo emissions testing while driving on the road. NOx emission levels during RDE testing will be limited to a maximum of 2.1 times the Euro 6 limit (168 mg/km) until September 2019, when the RDE emissions limit will be lowered to 1.5 times the Euro 6 limit (120 mg/km).

However, the RDE regulation needs to be further developed to meet those limits, says the ICCT.

Unlike the name suggests, the RDE regulation does not fully cover the real-driving conditions of normal vehicles. This is because a number of driving situations, such as driving at unusually cold or hot temperatures or driving at higher speeds, are still excluded in the current version of RDE testing. Also, vehicle manufacturers can decide which vehicle to test—typically a carefully prepared prototype version. They can carry out the testing themselves and thereby optimize the results.

—Dr. Peter Mock, Managing Director of ICCT in Europe

Vehicles with defeat devices installed have an especially large impact on average NOx emission levels.

The RDE regulation is an important step in the right direction. But the current version of RDE is not designed to detect defeat devices, and without further provisions to test in-service vehicles rather than prototypes and to expand the range of driving conditions covered by the test, resulting real-world emission levels will be higher than the adopted RDE emission limits suggest.

—Joshua Miller, ICCT researcher co-author

The European Commission, against resistance of some vehicle manufacturers and EU member states, is planning to introduce regular spot checks for randomly selected vehicles and force governments to impose financial penalties and recalls if on-road emissions are found to be too high. The issue will be brought forward for discussion as part of a working group meeting on 17 January 17 in Brussels.

Although the planned move by the European Commission is welcome, a realistic view is needed with respect to timing, the ICCT says.

Even in our most optimistic scenario, with a substantial improvement in NOx technology applications and enforcement practices, we expect the average real-world NOx emissions level of new diesel cars to drop to 96 mg/km only in 2022. This highlights the need for further tightening vehicle emissions testing procedures. Otherwise, diesel car NOx emissions will remain above the regulatory limit for many years to come, and at levels much higher than those of gasoline cars.

—Joshua Miller

The analysis also shows that at the local level, a 50% reduction in NOx emissions could occur 8 years sooner via introduction of a low-emission zone that progressively excludes older diesel cars from entering the city center.



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