Pollutants Overview

Air quality pollutants measured are described below. Click a link below to jump directly to the text.

• Nitrogen dioxide (NO₂)
• Fine Particles (PM₁₀, PM_2.5 and PM₁)
• Ozone and volatile organic compounds
• Benzene
• 1,3-Butadiene
• Toxic Organic Micro-Pollutants (TOMPS)
• Lead and Heavy Metals
• Sulphur dioxide (SO₂)
• Carbon monoxide (CO)
• Nitric oxide (NO)
• Carbon dioxide (CO₂)

Nitrogen dioxide (NO₂)

Nitrogen dioxide can irritate the lungs and lower resistance to respiratory infections such as influenza. Continued or frequent exposure to concentrations that are typically much higher than those normally found in the ambient air may cause increased incidence of acute respiratory illness in children.

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Fine Particles (PM₁₀, PM_2.5 and PM₁)

Fine Particles are composed of a wide range of materials arising from a variety of sources including:

• combustion sources (mainly road traffic)
• secondary particles, mainly sulphate and nitrate formed by chemical reactions in the atmosphere, and often transported from far across Europe
• coarse particles, suspended soils and dusts (e.g. from the Sahara), seasalt, biological particles and particles from construction work

Particles are measured in a number of different size fractions according to their mean aerodynamic diameter. Most monitoring is currently focussed on PM₁₀, but the finer fractions such as PM_2.5 and PM₁ are becoming of increasing interest in terms of health effects. Fine particles can be carried deep into the lungs where they can cause inflammation and a worsening of the condition of people with heart and lung diseases. In addition, they may carry surface-absorbed carcinogenic compounds into the lungs.

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Ozone and volatile organic compounds

Ozone (O₃) is not emitted directly from any man-made source in any significant quantities. In the lower atmosphere, O3 is primarily formed by a complicated series of chemical reactions initiated by sunlight. These reactions can be summarised as the sunlight-initiated oxidation of volatile organic compounds (VOCs) in the presence of nitrogen oxides (NO_x). The sources of VOCs are similar to those described for NO_x above, but also include other activities such as solvent use, and petrol distribution and handling.

The chemical reactions do not take place instantaneously, but can take hours or days, therefore ozone measured at a particular location may have arisen from VOC and NO_x emissions many hundreds or even thousands of miles away. Maximum concentrations, therefore, generally occur downwind of the source areas of the precursor pollutant emissions. Ozone irritates the airways of the lungs, increasing the symptoms of those suffering from asthma and lung diseases.

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Benzene

Benzene is a VOC which is a minor constituent of petrol. The main sources of benzene in the atmosphere in Europe are the distribution and combustion of petrol. Of these, combustion by petrol vehicles is the single biggest source (70% of total emissions).

Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.

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1,3-Butadiene

1,3-butadiene, like benzene, is a VOC emitted into the atmosphere principally from fuel combustion of petrol and diesel vehicles. 1,3-butadiene is also an important chemical in certain industrial processes, particularly the manufacture of synthetic rubber.

Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.

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Toxic Organic Micro-Pollutants (TOMPS)

TOMPs are produced by the incomplete combustion of fuels. They comprise a complex range of chemicals some of which, although they are emitted in very small quantities, are highly toxic or carcinogenic. Compounds in this category include:

• PAHs (PolyAromatic Hydrocarbons)
• PCBs (PolyChlorinated Biphenyls)
• Dioxins
• Furans

TOMPS can causing a wide range of effects, from cancer to reduced immunity to nervous system disorders and interfere with child development. There is no "threshold" dose - the tiniest amount can cause damage.

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Lead and Heavy Metals

Since the introduction of unleaded petrol in the UK there has been a significant reduction in urban lead levels. In recent years industry, in particular secondary non-ferrous metal smelters, have become the most significant contributors to emissions of lead. The highest concentrations of lead and heavy metals are now therefore found around these installations in industrial areas.

Even small amounts of lead can be harmful, especially to infants and young children. In addition, lead taken in by the mother can interfere with the health of the unborn child. Exposure has also been linked to impaired mental function, visual-motor performance and neurological damage in children, and memory and attention span.

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Sulphur dioxide (SO₂)

Sulphur dioxide (SO₂) is produced when a material, or fuel, containing sulphur is burned. Globally, much of the sulphur dioxide in the atmosphere comes from natural sources, but in the UK the predominant source is power stations burning fossil fuels, principally coal and heavy oils. Widespread domestic use of coal can also lead to high local concentrations of SO₂.

Even moderate concentrations may result in a fall in lung function in asthmatics. Tightness in the chest and coughing occur at high levels, and lung function of asthmatics may be impaired to the extent that medical help is required. Sulphur dioxide pollution is considered more harmful when particulate and other pollution concentrations are high.

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Carbon monoxide (CO)

Carbon Monoxide (CO) is a colourless, odourless poisonous gas produced by incomplete, or inefficient, combustion of fuel. It is predominantly produced by road transport, in particular petrol-engine vehicles.

This gas prevents the normal transport of oxygen by the blood. This can lead to a significant reduction in the supply of oxygen to the heart, particularly in people suffering from heart disease.

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Nitric oxide (NO)

Nitric oxide (NO) is mainly derived from road transport emissions and other combustion processes such as the electricity supply industry. NO is not considered to be harmful to health. However, once released to the atmosphere, NO is usually very rapidly oxidised to nitrogen dioxide (NO₂), which is harmful to health. NO₂ and NO are both oxides of nitrogen and together are referred to as nitrogen oxides (NO_x).

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Carbon dioxide (CO₂)

Carbon dioxide (CO₂) is produced when a material, or fuel, containing carbon is burned. Globally, much of the carbon dioxide in the atmosphere comes from natural sources, but increasingly humans are adding carbon dioxide to the atmosphere through the combustion of fossil fuels for energy

CO₂ displaces oxygen in the air and in confined spaces can lead to shortness of breath and headaches. CO₂ is also an important greenhouse gas, contributing to climate change. It can also cause acid rain, when it interacts with moisture in the atmosphere to form a carbonic acid.

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