Technical Standards

Euro 1–6

EU emission limits for each standard are summarized in the following tables. All dates listed in the tables refer to new type approvals. The regulations also specify a second date—usually one year later, unless indicated otherwise—which applies to first registration (entry into service) of existing, previously type-approved vehicle models.

Durability

Useful vehicle life for the purpose of emission regulations is:

• Euro 3 stage: 80,000 km or 5 years (whichever occurs first); in lieu of an actual deterioration run, manufacturers may use the following deterioration factors:
  • Positive ignition: 1.2 for CO, HC, NO_x
  • Compression ignition: 1.1 for CO; 1.0 for NO_x and for HC+NO_x; 1.2 for PM
• Euro 4 stage: 100,000 km or 5 years, whichever occurs first.
• Euro 5/6 stage: In-service conformity—100,000 km or 5 years; durability testing of pollution control devices for type approval—160,000 km or 5 years (whichever occurs first); in lieu of a durability test, manufacturers may use the following deterioration factors:
  • Positive ignition (both for Euro 5 and Euro 6): 1.5 for CO; 1.3 for HC; 1.6 for NO_x; 1.0 for PM and PN
  • Compression ignition, Euro 5: 1.5 for CO; 1.1 for NO_x and HC+NO_x; 1.0 for PM and PN. Euro 6 deterioration factors to be determined.

Testing

Emissions are tested over the Worldwide harmonized Light vehicles Test Procedure (WLTP). Introduced between September 2017 and September 2019 for the type approval of light duty vehicles in the EU, the WLTP replaces the former New European Driving Cycle (NEDC) chassis dynamometer test procedure.

In addition to the WLTP laboratory tests, the Real-Driving Emissions (RDE) test has been adopted. This four-part package regulation was introduced over the course of three years between September 2017 and September 2020 for the type approval of light duty vehicles in the EU. The RDE test uses a portable emissions measurement system (PEMS) to determine NOX, PN, and CO emissions when driving on public roads. The route driven includes urban, rural, and motorway portions. Pollutant limits are only defined for NOX and PN and are defined as the corresponding Euro 6 limit multiplied by a conformity factor. This allows vehicles to be measured with higher pollutant levels during an RDE test than the Euro 6 standard by including the measurement uncertainty of PEMS. The purpose of the RDE test is to ensure that vehicle emissions do not significantly differ between laboratory tests and on-road driving.

Fuel Quality

The Euro 3 and Euro 4 standards were preceded by the introduction of more stringent fuel regulations that required a minimum diesel cetane number of 51 (beginning in 2000), a maximum diesel sulfur content of 350 ppm in 2000 and 50 ppm in 2005, and a maximum petrol (gasoline) sulfur content of 150 ppm in 2000 and 50 ppm in 2005. Sulfur-free diesel and gasoline fuels (≤ 10 ppm S) needed to be available from 2005 and became mandatory in 2009.

Key Features

Euro 1 and 2

Euro 1 standards (also known as EC 93), were mandated under Directive 91/441/EEC for passenger cars only. They were then updated under Directive 93/59/EEC to include both passenger cars and light trucks. Euro 2 standards were mandated under EC 96: Directives 94/12/EC or 96/69/EC.

To meet Euro 1 requirements, manufacturers in Europe used three-way catalytic converters in gasoline vehicles. These converters reduce NO_x into nitrogen gas and oxidize carbon, hydrocarbons, and carbon monoxide (CO) into CO₂.

Euro 3 and 4

Euro 3 and 4 standards were mandated under Directive 98/69/EC, with further amendments added under Directive 2002/80/EC. Euro 3 added NO_x-specific limits in addition to HC+NO_x limits. Positive ignition vehicles were exempt from PM standards through the Euro 4 stage.

In Europe, diesel oxidation catalysts (DOCs) were widely used to comply with Euro 3 and Euro 4 standards. A DOC is a flow-through device that replaces the muffler and makes use of precious metals to oxidize CO, gaseous hydrocarbons (HC), and liquid hydrocarbon particles (unburned fuel and oil). DOCs reduce overall PM mass and many toxic organic compounds but are not as effective as catalyzed diesel particle filters in controlling the large number of fine and ultra-fine particles in diesel exhaust.

Euro 5

For diesel engines, Euro 5 has two sets of limits scheduled for implementation: Euro 5a and Euro 5b. For gasoline engines, there is only one set of standards, referred to as Euro 5. Implementation of Euro 5 and Euro 5a began in 2009. Euro 5b went into effect in 2011.

The Euro 5b legislation also introduced a particle number (PN) emission limit (in addition to the mass-based limits) of 6.0×1011/km. Euro 5 improves on Euro 4 by focusing on tailpipe particulate matter emissions from diesel cars. Euro 5 mandates PM emissions be reduced to 5 mg/km which effectively forced the widespread application of diesel particle filters (DPFs).

Euro 6

In 2014, Europe introduced Euro 6 standards. Euro 6 diesel standards decrease NO_x limits by 56% compared to Euro 5 standards and therefore led to the widespread introduction of NO_x exhaust aftertreatment systems. The PN limit for diesel vehicles did not change from Euro 5. Because gasoline direct injection engines have gained relevance in recent years, a particle number emission limit for gasoline vehicles was defined in Euro 6 (phased in over the first three years of the standard). The PN limit for direct injection gasoline vehicles was phased in over three years and has also been the same for diesel vehicles since 2017. No limit applies for PM and PN emissions for indirect injection gasoline engines.

Technology

The following figure, from the International Council on Clean Transportation, summarizes compliance approaches for Euro 5 and 6 engines.