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Vehicle emissions: NOx, CO2… What’s the difference?

Émissions polluantes véhicules diesel essence

These days, it’s not easy to find your bearings when choosing a vehicle. There are many manufacturers and models to choose from, and emissions issues are tricky to deal with. European and domestic regulations will also influence your choices. What solutions are there reduce your vehicle’s impact? Let’s starting by taking a look at emissions from vehicles on the road.


Differences between CO2 and NOx


Nitrogen oxides (NOx), along with carbon monoxide (CO), fine particles and light hydrocarbons, are part of a category of “regulated” pollutants that affect air quality. Carbon dioxide (CO2), meanwhile, is not considered a pollutant but contributes to global warming, since it is the main greenhouse gas emitted by vehicles.


Carbon dioxide

Carbon dioxide – also called CO2 – is a gas that is naturally present in the Earth’s atmosphere. Though it is essential to life on Earth, it is also one of the causes of climate change.


Greenhouse gases are a natural phenomenon. They absorb some of the radiation the Earth emits into space, giving it a temperate climate that supports life. However, the widespread use of fossil fuels (petrol, natural gas, coal) has led to an increase in emissions of these gases, causing excessive warming. While carbon dioxide contributes to the balance of life on earth, its increase unfortunately contributes to its imbalance.


Nitrogen oxides (NOx)

Nitrogen oxides, including nitrogen dioxide, affect air quality. They are typically formed during combustion (in car engines, for example), and can cause respiratory problems and other ailments, including asthma.


Among nitrogen oxides, the main air pollutants are NO and NO2, which are grouped under the term NOx. Road traffic is responsible for more than half of these emissions. In addition, nitrogen dioxide contributes to the formation of ozone, another pollutant.


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Emissions: diesel vs. petrol


Due to their increased efficiency, diesel engines consume less fuel and emit less CO2 per km travelled than those that run on petrol. A diesel vehicle, however, produces more NOx than a petrol vehicle. However, technologies designed to reduce nitrogen oxide emissions have been installed on all new diesel vehicles for about ten years. SCR systems, for instance, which run on AdBlue®, can be installed to treat almost all NOx emissions.



Using AdBlue® to reduce NOx


To preserve air quality, the European Union has introduced standards to regulate vehicle pollutant emissions (Euro 1 to Euro 6). Manufacturers must comply with them to sell their vehicles within the EU.


Since the introduction of Euro 6, all new light diesel vehicles have been fitted with a nitrogen oxide treatment system. The most popular system is the SCR (Selective Catalytic Reduction) system, which works together with AdBlue®. AdBlue® is an aqueous solution composed of urea and demineralised water, which converts a significant portion of nitrogen oxides into harmless water vapour and nitrogen.


Need AdBlue®? Find the nearest TotalEnergies service station with AdBlue® available in bottles in the shop and for certain stations via dedicated AdBlue® pumps.