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.

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.

A catalytic converter converts exhaust emissions into water and carbon dioxide

Catalytic converters work at extremely high temperatures, approximately 400–600 °C. This 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.

Driving at high engine speeds with heavy acceleration can reduce the efficiency of the catalytic converter, which may increase emissions of substances such as hydrocarbons and nitrogen oxides.

Carbon monoxide poisoning

Carbon monoxide is an odourless and colourless gas found in exhaust emissions. Because it cannot be detected by smell or sight, it is very dangerous. Carbon monoxide is harmful because it reduces the blood's ability to transport oxygen. If you are exposed to exhaust gases and develop a headache or start to feel unwell, you must get fresh air immediately to avoid carbon monoxide poisoning.

Carbon monoxide poisoning can occur:

• 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.
• If your car's exhaust system is leaking.

If you suspect your car's exhaust system is leaking, you should have it checked by a workshop as soon as possible. This is important because exhaust gases could otherwise leak into the vehicle.

Always wind up the windows when driving in tunnels

Emissions and problems

Vehicle traffic does not only affect the climate. It also worsens air quality and can cause serious problems for both the environment and human health.

Not all harmful particles in traffic environments come from exhaust gases. A large share of the particle levels in the air can also come from wear on tyres, brakes, and the road surface, as well as from road dust that is stirred up.

Several thousand people in Sweden are estimated to die prematurely each year, mainly from cancer and acute heart and lung diseases, as a result of traffic-related air pollution, that is, both exhaust gases and wear particles. Significantly more people die from traffic-related air pollution than in 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 allow them to absorb heat radiation that is leaving the Earth. 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 amount of greenhouse gases in the atmosphere increases, for example due to carbon dioxide emissions, the greenhouse effect becomes stronger. This causes global temperatures to rise, which in turn leads to the melting of polar ice caps, animal species being eradicated and an increase in the occurrence of natural disasters and extreme weather events.

Road traffic contributes to the greenhouse effect through large carbon dioxide emissions. In Sweden, road traffic accounts for about 30% of carbon dioxide emissions.

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

Other emissions and problems

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

Nitrogen oxides (NO_X) – Acidify soil and water and contribute to eutrophication in lakes and oceans, which can lead to algal blooms, oxygen depletion and dead zones. They can also damage DNA and irritate the airways and mucous membranes. Together with hydrocarbons, they contribute to the formation of ground-level ozone.

Hydrocarbons (HC) – Can damage DNA and cause cancer. Together with nitrogen oxides, they contribute to the formation of ground-level ozone.

Ground-level ozone – Ozone high up in the atmosphere protects us from the sun's radiation. However, when ozone forms near the ground – for example due to emissions of hydrocarbons and nitrogen oxides – it becomes harmful to both humans and the environment. It can irritate the airways and lungs, disrupt photosynthesis and damage the water balance of plants.

Soot and harmful particles – In areas with vehicle traffic, we are exposed to soot and particles from engine combustion and road wear. These can cause respiratory problems and cancer.

Noise – Noise is disturbing, can cause stress and other health problems, and has a negative impact on people's well-being and health. About two million Swedes are exposed to traffic noise in their homes.

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 an environmental zone, certain vehicles are not allowed to drive. There are three different classes of environmental zones.

Environmental zone class 1 applies to heavy trucks and buses. Environmental zone class 2 covers passenger cars, light buses, and light trucks that meet certain emission requirements, while environmental zone class 3 has the strictest requirements and mainly allows electric, fuel cell, and gas-powered vehicles.

Biofuel

Biofuels such as ethanol and biogas are renewable fuels produced from living organisms, known as biomass. Unlike fossil fuels such as petrol, diesel, natural gas and coal – which take millions of years to form – biomass is continuously produced in nature.

One of the main advantages of biofuels is that they do not increase the greenhouse effect in the same way as fossil fuels. When biofuels are burned, they release carbon dioxide, but the amount is roughly equal to what the plants absorbed during their growth. Therefore, biofuels are part of the natural carbon cycle.

Ethanol fuel (E85), however, contains a certain proportion of fossil petrol, and both the production and transportation of biofuels require energy – which sometimes comes from fossil sources. For this reason, biofuels are rarely completely climate neutral. Nevertheless, the use of biofuels contributes far less to the greenhouse effect than petrol and diesel.

The use of biofuels does not increase the greenhouse effect in the same way as fossil fuels

Quick review

• Catalytic converters clean most harmful substances in exhaust emissions.
• Catalytic converters do not reduce carbon dioxide emissions.
• Lower fuel consumption reduces carbon dioxide emissions.
• Catalytic converters work less effectively during cold starts.
• Carbon monoxide is colourless, odourless and very dangerous to inhale.
• Traffic-related air pollution can cause serious health problems.
• Harmful particles come both from exhaust emissions and from wear on tyres, brakes and the road surface.
• Road traffic contributes to the greenhouse effect through large carbon dioxide emissions.
• Carbon monoxide, nitrogen oxides and hydrocarbons are harmful substances.
• Environmental zones restrict which vehicles are allowed to drive in certain areas.
• Biofuels affect the climate less than fossil fuels.