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There are seven main pollutants - carbon monoxide, nitrogen dioxide, ground level ozone, particulate matter, sulphur dioxide, hydrocarbons and lead.

Air pollution is made up of a mixture of gases and particles that have been released into the atmosphere by man-made processes.

Emissions are typically from the combustion of fossil fuels such as coal, oil, petrol or diesel. The sources, health effects and chemical behaviour of each separate pollutant are different, making the task of understanding and controlling air pollution as a whole very complex.

While it is us who produce the pollution, it is primarily the weather that dictates what will happen once it is released into the air.

During wet or windy conditions pollution levels remain low, either blown away and dispersed to harmless levels, or removed from the air by rain. During certain conditions pollution levels are able to build up to harmful levels leading to pollution 'episodes'.

Please also see "what are the causes of air pollution" information from DEFRA

Where the highest levels of pollutant are generally found in the environment where we live

Pollutant

Where the highest levels are generally found in the environment where we live
Carbon monoxide concentrations will generally be highest close to busy roads
Nitrogen dioxide as above
Particulate matter as above
Ozone due to complex atmospheric chemistry, levels will generally be highest in rural areas during the summer months
Sulphur dioxide concentrations are highest in the vicinity of large industrial combustion processes
Hydrocarbons close to roads and large industrial combustion processes, these contribute to the formation of ground level ozone
Benzene and 1,3 butadiene generally highest close to busy roads and in the vicinity of petrol filling stations