These are the main ambient air pollutants and their sources:

Particulate Matter (PM10 and PM2.5)

Particulate matter (PM) is a complex pollutant as it contains a variety of components in variable concentrations. The principal source of particulate matter in European cities is road traffic emissions, particularly from diesel vehicles. It is also emitted from industrial combustion plants and public power generation, commercial and residential combustion, and some non-combustion processes (e.g. quarrying). Natural sources include volcanoes, dust storms and sea salt. Whilst these generally produce only a small percentage of fine particulate matter they can contribute significantly to local breaches of the regulatory limit. Levels of PM are highest in urban areas as they are a traffic-related pollutant. Secondary sources, from material originally in gaseous form have been taken up into the particulate phase and include: sulphuric acid and ammonium sulphate from oxidation of sulphur dioxide; ammonium and other nitrates derived from oxidation of nitrogen oxides; and semi-volatile organic compounds.

Particulate matter is categorised according to its size in micrometers. PM10 refers to particles under 10 micrometers, sometimes called the ‘coarse fraction’. PM2.5 refers to particles under 2.5 micrometers, sometimes called the ‘fine fraction’. PM2.5 is thought to be more damaging to human health than PM10.

Find out more about Particulate Matter

Nitrogen Dioxide (NO2)

Nitric oxide (NO) is produced during high temperature burning of fuel (e.g. road vehicles, heaters and cookers). When this mixes with air, NO2 is formed. Levels are highest in urban areas as it is a traffic-related pollutant.

Ozone (O3)

Ground level ozone is a secondary pollutant; it is formed through a chemical reaction of volatile organic compounds and nitrogen dioxide in the presence of sunlight, so levels are generally higher in the summer. The highest levels tend to be found in rural areas downwind of urban areas or industrial sites.

Sulphur Dioxide (SO2)

Fossil fuel combustion (principally power stations), conversion of wood pulp to paper, manufacture of sulphuric acid, smelting, incineration of refuse. The most common natural source is volcanoes.

Volatile Organic Compounds (VOCs)

Benzene The main source of atmospheric benzene in Europe is petrol vehicles, which accounts for about 70% of emissions. Another 10% comes from the distillation, refining and evaporation of petrol from vehicles.

Other VOCs play a role in the photochemical formation of ozone in the atmosphere.

1,3-Butadiene The main source of 1,3-Butadiene is also principally from road traffic, in the combustion process of petrol and diesel vehicles. Unlike benzene it is not a constituent of fuel but is produced through the combustion of olefins. An additional source is from industrial processes such as synthetic rubber manufacture.

Carbon Monoxide (CO)

CO forms when carbon fuels are burned, either in the presence of too little oxygen or at too high a temperature. One of the main causes is idling vehicle engines and vehicle deceleration. Smaller amounts are released into the atmosphere from organic combustion in waste incineration and power station processes. Levels are highest in urban areas due to its close association with road traffic. However, in the UK levels are generally low being well below the targets set by the Government.

Lead (Pb)

As much of the airborne emission of lead originates from road traffic, concentrations have decreased with most cars running on unleaded and lead replacement petrol. Other sources of lead pollutants include waste incineration and metal processing. The largest industrial use is manufacturing batteries.

Toxic Organic Micro-Pollutants (TOMPs)

PAHs (Polycyclic Aromatic Hydrocarbons), PCBs (Polychlorinated Biphenyls), Dioxins, Furans
Produced by the incomplete combustion of fuels, road transport and industrial plant are the largest source. Open burning is a major source in the UK and comparatively large amounts are released on and around bonfire night, whilst there is increasing concern over domestic wood burning for heating. Tobacco smoke is also a source.

Effects of Air Pollution

Air pollution can affect human health, plants, animals and ecosystems, and the built environment.

Effects on Plants and Ecosystems

You can find out about the impact of air pollutants on UK habitats and species at the Department for Environment (DEFRA) website:

Effects on Human Health

To find out about air pollution and health visit the Public Health England website at:

Effects on Buildings

To find out about the impact of air pollutants on buildings visit the Buildings Research Establishment website.

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