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Smoke coming out of a factory.

What are the causes of air pollution

Below is an introduction to the principal pollutants produced by industrial, domestic and traffic sources: View a glossary for terms used in air pollution.

  • Sulphur dioxide
  • Nitrogen oxides
  • Particular matter (PM10, PM2.5 and PM1)
  • Ozone and volatile organic compounds
  • Toxic Organic Micro-Pollutants (TOMPS)
  • Benzene
  • 1,3-Butadiene
  • Carbon monoxide
  • Lead and heavy metals

Download a detailed list of the above pollutants - What are the causes of Air Pollution (PDF 139KB).

Historically, the main air pollution problem in both developed and rapidly industrialising countries has typically been high levels of smoke and sulphur dioxide emitted following the combustion of sulphur-containing fossil fuels such as coal, used for domestic and industrial purposes. These days, the major threat to clean air is now posed by traffic emissions. Petrol and diesel-engined motor vehicles emit a wide variety of pollutants, principally carbon monoxide (CO), oxides of nitrogen (NOx), volatile organic compounds (VOCs) and particulate matter (PM10), which have an increasing impact on urban air quality. In addition, pollutants from these sources may not only prove a problem in the immediate vicinity of these sources, but can be transported long distances.

Photochemical reactions resulting from the action of sunlight on nitrogen dioxide (NO2) and VOCs, typically emitted from road vehicles, lead to the formation of ozone. Ozone is a secondary pollutant, which often impacts rural areas far from the original emission site as a result of long-range transport.

In all except worst-case situations, industrial and domestic pollutant sources, together with their impact on air quality, tend to be steady or improving over time. However, traffic pollution problems are worsening world-wide.

Because of their potential impacts on human health, welfare and the natural environment, ambient concentrations for a number of these pollutants are measured continuously at a wide range of rural and urban locations throughout the UK.