Euro 6

Euro 6 is the European Union emissions standard that defines the maximum quantities of harmful pollutants a new car may legally emit, and it represents the strictest tier in a regulatory series that began with Euro 1 in 1992. It came into force for new type approvals in September 2014 and for all newly registered cars in September 2015, progressively tightening through sub-stages such as Euro 6b, 6c, 6d-TEMP and 6d. The standard exists to protect air quality and public health, targeting pollutants linked to respiratory illness, smog and environmental damage in densely populated urban areas.

The regulation sets specific numerical caps, measured in milligrams or grams per kilometre, on several pollutants: oxides of nitrogen (NOx), particulate matter (both by mass and, for many engines, by particle number), carbon monoxide and unburnt hydrocarbons. Its most consequential change concerned diesel engines, whose permitted NOx emissions were slashed to 80 mg/km, roughly halving the Euro 5 limit and bringing diesels much closer to the figures required of petrol cars. This single requirement reshaped diesel engineering across the industry.

Meeting these limits forced manufacturers to fit sophisticated after-treatment hardware. Diesel cars widely adopted selective catalytic reduction (SCR), which injects a urea solution marketed as AdBlue into the exhaust to chemically convert NOx into harmless nitrogen and water. Diesel particulate filters became universal, and exhaust gas recirculation was refined to suppress NOx formation during combustion. Many direct-injection petrol engines later gained gasoline particulate filters to satisfy the tightened particle-number limits.

A defining feature of the later stages was the introduction of Real Driving Emissions (RDE) testing. Earlier standards were verified only in the laboratory, and the diesel emissions scandal of 2015 exposed how poorly those bench results reflected on-road behaviour. From Euro 6d-TEMP onwards, cars also had to demonstrate compliance during real journeys using portable emissions measurement equipment, with a defined conformity factor allowing a limited margin above the laboratory figure. This closed much of the gap between certified and actual pollution.

In practice, Euro 6 compliance has become a key reference point for vehicle owners. It determines eligibility for many low-emission and clean-air zones across European cities, affects resale value, and is frequently cited in used-car listings as a marker of relative cleanliness. Diesel cars predating Euro 6 in particular face increasing access restrictions.

Euro 6 sits within a broader emissions framework and is closely tied to the technologies it mandated. Understanding it requires familiarity with NOx emissions, the diesel particulate filter, selective catalytic reduction and the Real Driving Emissions procedure, each of which addresses a distinct facet of the standard's demands. It is the direct predecessor to the forthcoming Euro 7 regulation.