Accelerating progress from Euro 4/IV to Euro 6/VI vehicle emissions standards

After the adoption of Euro 5/V standards in the EU, certain shortcomings in the regulation became apparent. For heavy-duty vehicles, Euro V standards have not achieved hoped-for reductions for NOx emissions. And while Euro 5 standards have resulted in dramatic reductions in PM emissions from light-duty diesels, real-world diesel NOX emissions have continued to exceed certification limits. Regulators should weigh these regulatory weaknesses when considering whether to move directly to Euro 6 and VI or to include the intermediate stages.

The type-approval process is critical to ensuring that reductions in limit values translate into reductions in real-world emissions from light- and heavy-duty vehicles. The process specified for both Euro IV and V HDV standards does not ensure that NOx controls operate effectively in urban driving conditions. For LDVs, the current type-approval procedure allows certification of vehicles with real-world NOx emissions far above regulatory limits.

These problems with type-approval procedures have been addressed: for HDVs, through the move to World Harmonized Test Cycles and efforts to improve real-world conformity to NOx limits in Euro VI, and for LDVs in the Real-World Driving Emissions (RDE) provision of Euro 6c and the transition from the NEDC to the World-Harmonized Light-Duty Test Procedure (WLTP). While Euro 5 standards have forced use of diesel particulate filters for light-duty diesels, the Euro VI standard introduces a particle number limit for heavy-duty vehicles, which necessitates the use of diesel particulate filters for all diesel vehicles.

Given the availability of ultra-low sulfur fuel (sulfur content less than 10 ppm), greater air-quality benefits can be gained from a leap from Euro 4/IV to Euro 6/VI than a path that includes the intermediate Euro 5/V stage. For countries that are at prior standards for heavy-duty vehicles, accelerating the adoption of Euro VI standards has twofold benefits for air quality: the use of DPFs to comply with new PM and PN limits leads to a 90% or greater reduction of PM2.5 emissions, and the new test cycle and in-service conformity requirements provide real-world reductions in NOx emissions of 95% or more, providing emission control even in urban driving conditions that remained a problem in Euro V. Light-duty Euro 6 standards promise a similar reduction in real-world NOx emissions from diesel cars, through tighter emissions limits, a future move to the WLTP, and the inclusion of PEMS testing in the type approval process to ensure conformity to standards in actual driving conditions.

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