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Vehicle exhaust emissions

Exhaust systems

A vehicle's exhaust system consists of one or more mufflers and a catalytic converter. Catalytic converters purify about 80-95% of the harmful substances in exhaust emissions, converting them to carbon dioxide and water.

A catalytic converter converts exhaust emissions into water and carbon dioxide

Catalytic converters do not reduce carbon dioxide emissions. The only way to reduce these is by decreasing fuel consumption – therefore, choose a car that is as fuel-efficient as possible, leave it at home whenever you can and drive economically.

Catalytic converters work at extremely high temperatures (approximately 400-600 °C), which means two things:

  • They are ineffective during cold starts – therefore use an engine pre-heater.
  • There is a risk of fire. For example, it can be hazardous to park on a lawn with dry high grass, as catalytic converters are usually placed on the vehicle's undercarriage.

It is important not to accelerate the engine to more than half-throttle, or to exceed 3,000 rpm. If you do, a catalytic converter can stop working properly. If this happens, the emission of substances hazardous to health and the environment, such as hydrocarbons and nitrogen oxides, increases.

Carbon monoxide poisoning

Carbon monoxide is both odourless and colourless and is therefore very dangerous. If you are exposed to exhaust emissions and get a headache or start feeling unwell, you must get fresh air as soon as possible to avoid carbon monoxide poisoning.

Carbon monoxide poisoning can occur:

  • If your car's exhaust system is leaking.
  • If you drive in heavy traffic or in a tunnel with the windows rolled down or the trunk lid open.
  • If you are in a garage or other closed space where a vehicle is idling.

Always wind up the windows when driving in tunnels

If you suspect your car's exhaust system is leaking you can try to find the leak by sealing the exhaust pipe while the car is idling, and then looking for exhaust emissions under the car. This should be done outside – not indoors, in a garage or the like, as that could lead to carbon monoxide poisoning.

Emissions and problems

Most people know that carbon dioxide emissions from vehicle traffic are a contributing factor to the greenhouse effect. Unfortunately, traffic and exhaust emissions also cause a number of other environmental and health-related problems.

Approximately 1,000-3,000 Swedes per year are estimated to die, mainly from cancer and acute heart and lung diseases, as a result of air pollution from traffic (exhaust emissions and wear particles). Thus, there are considerably more people who die from air pollution from traffic than from traffic accidents.

The greenhouse effect

Earth is surrounded by an atmosphere that consists of several different gases. Some of these gases, including water vapor, carbon dioxide, methane and nitrous oxide, are so-called greenhouse gases.

Greenhouse gases have properties that prevent heat radiation from leaving our planet. This phenomenon is called the greenhouse effect and is necessary for all life on Earth. Without this protective atmosphere of gases, Earth would be about 30 degrees Celsius colder than it is today.

However, when the level of atmospheric greenhouse gases increases (for example, through carbon dioxide emissions), the greenhouse effect is strengthened. This causes global temperatures to rise, which in turn leads to the melting of polar ice caps, ozone depletion (making the ozone hole larger), animal species being eradicated and an increase in the occurrence of natural disasters.

Vehicle traffic is a contributing factor to the greenhouse effect and rising global temperatures

Other emissions and problems

Carbon monoxide (CO) – Harms the body's central nervous system and reduces the blood's ability to absorb oxygen.

Nitrogen oxides (NOX) – Acidify land and water, lead to eutrophication of lakes and oceans, and harm our genome, airways and mucous membranes. Together with hydrocarbons contribute to the formation of ground-level ozone.

Hydrocarbons (HC) – Affect our genome and cause cancerous diseases. Together with nitrogen oxides contribute to the formation of ground-level ozone.

Ground-level ozone – Ozone in the atmosphere protects against the sun's radiation, but when it is formed too close to the ground – due to, among other things, hydrocarbon and nitrogen oxide emissions – it is harmful to humans and the environment. Ground-level ozone irritates our mucous membranes and lungs, prevents photosynthesis and damages the water balance of plants.

Soot and harmful particles – In the vicinity of vehicle traffic, we constantly inhale soot and particles from engine combustion and road wear. This can lead to respiratory problems and cancers, among other things.

Noise – Noise disturbs and can also lead to stress and stress related diseases.

Infrasound – Motor vehicles also create sounds at such low frequencies that we do not hear them. These inaudible, yet impactful sounds can lead to concentration difficulties, headaches and fatigue.

Traffic emissions in Sweden have fallen in recent years, but air pollution levels are still too high in many places

Environmental zones

To improve air quality and reduce nitrogen oxide levels in environmentally sensitive areas, municipalities can implement special environmental zones. In environmental zones, certain vehicles are not allowed to drive. There are three different classes of environmental zones with different requirements on vehicle type and emissions. Class 3 environmental zone sets the highest requirements.

Class 1 environmental zone


Biofuels such as ethanol, biogas and rapeseed oil are renewable fuels produced by living organisms (biomass). Unlike fossil fuels – such as petrol, diesel, natural gas and coal – which take millions of years to form, biomass is constantly being created.

One of the major advantages of biofuels is that they do not contribute to the greenhouse effect. This is because the amount of carbon dioxide emitted when such fuels are combusted is equal to the amount of carbon dioxide that the plant (which the fuel consists of) consumed before it was harvested.

When fossil fuels are combusted, on the other hand, a surplus of carbon dioxide is released, which contributes to the greenhouse effect.

About 20% of all fuel currently used for road transport in Sweden is of non-fossil origin.

Bild på en katalysator The use of biofuels do not contribute to the greenhouse effect

Environmental statistics

  • In Sweden, there are approximately 4.7 million private cars and 7.4 million motor vehicles in traffic.
  • About 50% of all car journeys are shorter than five kilometres.
  • About 20% of all fuel currently used for road transport in Sweden is of non-fossil origin.
  • About 50% of nitrogen oxide emissions in Sweden come from vehicle traffic.
  • About 30% of carbon dioxide emissions in Sweden come from vehicle traffic.
  • Approximately 1,000-3,000 Swedes per year are estimated to die as a result of air pollution from traffic.
  • About two million Swedes are exposed to traffic noise in their homes.