Glossary

When fuels such as petrol and diesel are burned in the engine, carbon dioxide (CO₂) is produced and released into the atmosphere. Levels of CO₂ emissions are controlled under the ‘Euro’ standards classifications.

A diesel particulate filter is fitted to the exhaust of all Euro 5 and Euro 6 cars. It traps particulates before they leave the tailpipe.

EGR is a critical technology used to reduce the levels of NOx emitted by the engine. It involves recirculating exhaust gas back into the engine combustion chamber. This reduces the amount of oxygen, and lowers combustion temperature. Less oxygen and a lower combustion temperature reduces the amount of NOx formed.

Euro 6 is the sixth air quality emissions standard for new vehicles sold in Europe. The European Commission has enforced Euro standards since 1993. Each successive standard has been tougher in its requirements, ensuring that every new generation of vehicle uses the latest, cleanest engine and exhaust technology available.

A lean NOx trap or catalyst is an exhaust after-treatment technology, which reduces the emissions of NOx from the tailpipe (see below). It captures NOx and neutralises it in the exhaust system.

The NEDC is the EU’s official test of new cars’ air quality and CO2 emissions, and it has been in place since 1996. It is a laboratory test, which operates in strictly controlled conditions and is monitored by a government-appointed approval agency. In the UK, this is the Vehicle Certification Agency (VCA).

NOx refers to nitrogen oxides or oxides of nitrogen that form when fuels are burned at high temperatures, as in the engine combustion process.

Particulate matter, commonly known as soot, is a waste material of combustion.

PEMS, or portable emissions measurement system, is a sophisticated mobile laboratory in a box, which is fitted to the car and analyses tailpipe emissions while the vehicle is driven on the road or a test track.

Real world refers to conditions that affect a vehicle’s performance when it is being driven on the road, as opposed to being tested in a lab. Real world conditions are infinitely variable, making reliable and repeatable testing of emissions extremely difficult.

RDE stands for Real Driving Emissions and refers to the emissions that a car produces on the road while following a set procedure, rather than in a laboratory environment. On-road emissions can be affected by many different factors, including car and traffic conditions, temperature, weather, road surface and gradient, vehicle load and driving style.

Selective catalytic reduction (SCR) is a highly effective emissions reducing technology used in modern diesel vehicles. This specialist catalytic converter injects a urea based additive, or diesel exhaust fluid that’s often called AdBlue, into the exhaust to convert NOx into harmless nitrogen and water.

Type Approval is the official EU process new cars must pass before they can be certified for sale. It applies to many systems - emissions and safety. Cars must pass the relevant regulated tests before they are allowed to be put on the market. The VCA is the government-appointed Type Approval authority in the UK.