Burning fuels can release harmful pollutants. Carbon monoxide (CO) is made when fuel burns in a limited supply of oxygen, which is called incomplete combustion. Sources include petrol engines and faulty gas boilers. It is a colourless, odourless, toxic gas. It combines with haemoglobin in the blood and stops it carrying oxygen, so it causes headaches, loss of consciousness and death.
Sulfur dioxide (SO2) is made when fuels that contain sulfur, such as coal and some oil, are burned. It dissolves in rainwater to form acid rain, which damages buildings and harms plants and aquatic life. It also causes breathing problems.
Oxides of nitrogen (NOx) form inside hot engines, where nitrogen and oxygen from the air react together. They also cause acid rain and respiratory problems.
Particulates are tiny solid particles, such as soot (carbon) from incomplete combustion in diesel engines. They can damage the lungs and cause breathing problems, and they can cause global dimming, where less sunlight reaches the Earth's surface.