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Euro 6 And AdBlue: What Do They Mean For Us?

Euro 6 and AdBlue: what do they mean for us?

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Urban, regional and global air pollution challenges remain daunting: this is a fact.

Euro 6 and AdBlueVehicle emissions are a key talking point when it comes to environmental pollution and they are just one of many contributors to overall pollution.

Over the years, vehicle emissions have dropped as a result of ever-stricter legislation, although in recent years it has become clear that some car makers have struggled to meet legal requirements, as evidenced by the VW Group’s emissions cheating scandal.


When talking about emissions we mean nitrogen oxide (NOx), carbon monoxide (CO), hydrocarbons (THC and NMHC) and particles (PM), which is basically soot from diesel cars. The knock-on effect of reducing these pollutants can also mean improved fuel economy and lower CO2 emissions.

Euro 6 and AdBlueBefore entering the figures, it is worth remembering what effect each gas has in human beings:

NOx is a harmful pollutant that is often blamed for damaging the environment reacting with other compounds to give rise to other air pollutants, but has also been proven to have serious health implications due to respiratory problems. Particles, meanwhile, is a local pollutant that has also been linked to health problems.

Carbon monoxide is a poisonous gas because it causes cell asphyxiation by not letting oxygen through the blood.

Hydrocarbons are harmful to the respiratory tract.

Particles are harmful to health, causing respiratory and cardiovascular problems and in the long term and in high concentrations they produce cancer. They also produce a certain greenhouse effect.


European emission standards were established many years ago, which set emissions limits for the different exhaust gases of cars with internal combustion engines. They are known as Euro standards. The Euro 1 standard came into force in 1992. Now we are under Euro 6 standard.

Euro 6 is the sixth incarnation of the European Union directive to reduce harmful pollutants from vehicles which came into force in September 2014. All new cars homologated for sale in Europe must meet this standard. The Euro 6 standard affects both petrol cars and diesel cars and all mass-produced cars sold from this date onwards, they will all need to meet these emissions requirements. The aim of Euro 6 is to reduce levels of harmful car and van exhaust emissions, both in petrol and diesel cars.


The latest Euro 6 regulations set different emissions standards for petrol and diesel cars, but that is a reflection on the different kind of pollutants the two fuels produce. For diesels, the permitted level of NOx emitted has been dramatically dropped down to a maximum of 80mg/km, compared to the 180mg/km level that was required for cars that met the previous Euro 5 emissions standard. In contrast, the NOx limit for petrol cars remained unchanged from Euro 5, as it was already low at 60mg/km.

And now let’s see the limits of Euro 6:

Diesel engine

  • CO (carbon monoxide): 0.50 g / km
  • HC (total hydrocarbons): 0.09 g / km (approx.)
  • NOx (nitrogen oxides): 0,080 g / km
  • HC + NOx (hydrocarbons and nitrogen oxides): 0,170 g / km
  • PM (particles): 0.005 g / km

Petrol engine

  • CO (carbon monoxide): 1.0 g / km
  • HC (total hydrocarbons): 0.10 g / km
  • NOx (nitrogen oxides): 0,060 g / km
  • HC + NOx (hydrocarbons and nitrogen oxides): 0.160 g / km (approx.)
  • PM (particles): 0.005 g / km

Euro emissions standards for diesel cars evolution since Euro 1:

Euro standard Date CO NOx PM
Euro 1 July 1992 2.72 0.14
Euro 2 January 1996 1.0 0.08
Euro 3 January 2000 0.64 0.50 0.05
Euro 4 January 2005 0.50 0.25 0.025
Euro 5a September 2009 0.50 0.180 0.005
Euro 6 September 2014 0.50 0.080 0.005


Euro emissions standards for petrol cars evolution since Euro 1:

Euro standard Date CO NOx PM
Euro 1 July 1992 2.72
Euro 2 January 1996 2.2
Euro 3 January 2000 2.3 0.15
Euro 4 January 2005 1.0 0.08
Euro 5 September 2009 1.0 0.060 0.005
Euro 6 September 2014 1.0 0.060 0.005



Anyway, technology advances and there are multiple strategies to reduce the air pollution of the internal combustion engines. Car manufacturers have to resort to more complex injection systems, new high-tech materials (with less internal friction, higher resistance to high temperatures and pressures, lower weight), components that reduce emissions (exhaust gas compressor, exhaust gas recirculation) and various catalysts and filters in the exhaust line to remove most of the contaminants (catalyst, nitrogen oxides trap, antiparticle filter, selective catalytic reduction). Obviously, all these cars will have an increase in their production cost and they will have to be sold at a higher price.

The firsts strategies to reduce emissions in diesel cars were exhaust gas recirculation (EGR) which reduces emissions of nitrogen oxides, and the two-way catalytic converter (an oxidation catalyst, as well as cars petrol). But these two devices are no longer enough to commit with Euro 6.

With the Euro 6 standard the emissions of nitrogen oxides have to be reduced far beyond, and this means having to resort, depending on the engine and the car, to one of the following devices in the exhaust line:

  • Euro 6 and AdBlueNOX traps, a special type of catalyst with metals such as platinum, rhodium and barium, which together with a control of the oxygen level inside it, and high temperature, is able to neutralize nitrogen oxides.
  • Catalyst SCR, for selective catalytic reduction. It is also a special type of catalyst that uses an urea additive, which reacts chemically with the gases to neutralize nitrogen oxides. This additive may be the one known as AdBlue, among other trademarks which have already used trucks and buses for some years.
  • In the case of the SCR catalyst, a little tank and an additional refueling nozzle are required to fill the urea compound (AdBlue) which is spent.


AdBlue is the registered trademark of the AUS32 urea product (32,5% urea solution) used to reduce the emissions of nitrogen oxides (NOx) caused by diesel engine exhausts, through a process called Selective Catalytic Reduction (RCA) .

Euro 6 and AdBlueAs the name AUS32 (Aqueous Urea Solution) suggests, the product is a solution of high purity urea in demineralized water. Clear, non-toxic and safe to handle. However, it may be corrosive to some metals, and materials suitable for transportation and storage must be used. AdBlue is a registered trademark of the German Automobile Industry Association which ensures compliance with the quality standards according to the specifications set out in ISO 22241.

AdBlue is used by vehicles equipped with RCA technology, in which the product is stored in an exclusive warehouse.  Consumption of AdBlue is equivalent to 3-5% of fuel consumption. This low dosage allows to space the refills and to minimize the impact that produces in the chassis an additional tank.


With some honorable exceptions, it is normal that the more powerful diesel and larger vehicles should have to inexorably resort to this additive.

The ability of a manufacturer to make its diesel engines exceed Euro 6 without the need of this additive will depend on its technology. Using a very quick generalization, we will see how small engines for small passenger cars do not require an AdBlue system and are able to comply the Euro 6 homologation with a physical catalyst – the so-called NOx trap – that synthesize a good part of their emissions. On the other hand, the more powerful diesel and larger vehicles will require the use of an AdBlue system.


Written by Francisco Javier García

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