Motor vehicles emit the pollutants carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO_x). In addition, vehicles with diesel engines also emit particulate matter (PM). Emission levels for these pollutants are limited by standards that are binding throughout the EU (Euro standards).

Carbon monoxide (CO)
Insufficient intake of air results in incomplete combustion and the formation of carbon monoxide (CO), a colourless, odourless and tasteless gas. When inhaled, CO prevents the blood's absorption of oxygen and, depending on the concentration, causes headaches, nausea, or even death. Oxidation processes convert CO to CO₂.

Hydrocarbons (HC)
Diesel fuel and petrol consist of a mixture of hydrocarbons (HC). Even after combustion of the fuel, HCs remain in the exhaust gas. Aromatic hydrocarbons are classed as carcinogenic. They are formed during incomplete combustion or evaporation of fuel. Hydrocarbons react with nitrogen oxides and sunlight to form organic compounds that irritate the mucous membranes of the respiratory tract and are the main factor in causing summer smog.

Nitrogen oxides (NO_X)
NO is a colourless, odourless and tasteless gas that gradually converts in the ambient air to nitrogen dioxide or NO₂. NO₂ is toxic and has a pungent smell. NO and NO₂ are usually referred to jointly as NO_x.

Carbon dioxide (CO₂)
The natural greenhouse effect is one of the factors responsible for our climate. Without the protective layer in the stratosphere it would be at least 30°C colder. Humans and animals emit CO₂, which plants convert to oxygen during photosynthesis and which the oceans also absorb.

Particulate matter (PM)
Particulate matter, like elemental carbon, is suspected of causing cancer. The microscopically small particles of soot can enter the lungs via the respiratory tract.

Sulphur dioxide (SO₂)
A colourless, pungent smelling gas that is highly irritant. It reacts with water and sunlight to form a sulphurous acid, which as one of the main causes of acid rain, is responsible for forest dieback.