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Air quality
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Air pollutants

Nitrogen dioxide

Nitrogen dioxide is a brown gas, with the chemical formula NO2. It is chemically related to nitric oxide (nitrogen monoxide), a colourless gas with the chemical formula NO. These abbreviations are often used instead of writing the names of the chemicals in full. Together, NO and NO2 are known as NOX. NOX is released into the atmosphere when fuels are burned for example, petrol or diesel in a car engine, or natural gas in a domestic central heating boiler or power station.
NO2 can affect our health. There is evidence that high levels of it can inflame the airways in our lungs and, over a long period of time, affect how well our lungs work. People with asthma are particularly affected. NO2 can also affect vegetation.

Fine particles (PM10)

Fine particles (PM10) are particles with a diameter of less than 10 microns (µg) – a hundredth of a millimetre. The main source of airborne fine particles in the UK is road traffic emissions, particularly from diesel vehicles. Most of the PM10 released by the industry comes from the fuel and power sector and the metals sector. Fine particles are also formed by chemical reactions in the atmosphere, dust from construction work and industrial processes, and from dust that’s in the air naturally such as soil and silt.

Fine particles can harm health, especially if people already have breathing difficulties or lung disease. As they are so small, fine particles can penetrate deep into the lungs. Fine particles have been linked to respiratory disease and over the longer term, premature death.

Sulphur dioxide

Sulphur dioxide (SO2) is a colourless gas, released from burning fossil fuels such as coal and oil. It is one of the main chemicals that cause acid rain. Power stations and oil refineries are the main sources of sulphur dioxide in the UK but emissions are decreasing. Releases from other industries are relatively small. Sulphur dioxide is also found naturally in the air at low concentrations from natural releases such as volcanoes and forest fires.

Sulphur dioxide can cause breathing difficulties, is toxic to plants and can cause acid rain when it reacts with moisture in the air. Acid rain damages trees and other plants, and it can also affect the soil.

Carbon monoxide

Carbon monoxide (CO) is a gas made of one part carbon and one part oxygen. It is a colourless, odourless gas, about three per cent lighter than air, and is extremely poisonous to humans and many other forms of life. Breathing air that contains as little as 0.1 per cent carbon monoxide by volume can be fatal; a concentration of about one per cent can cause death within a few minutes.

Carbon monoxide forms when carbon or substances containing carbon are burned without a sufficient air supply. Faulty appliances that burn fossil fuels such as coal, wood, gas and oil can produce carbon monoxide if they are not properly ventilated. Carbon monoxide is also present in vehicle exhaust gases. Traffic is the main source of carbon monoxide in England and Wales.


Lead is released naturally through volcanic activity, rock weathering and when plants extract it from rocks and soil with other minerals. However human activities such as mining, ore smelting, lead production and burning fossil fuels also release lead into the environment. Lead production and industrial processes are now the main source of lead emissions. Most of the lead released by the industry comes from the metals sector (67 per cent in 2005). The chemicals sector (18 per cent) and the fuel and power sectors (10 per cent) also release large amounts.
Lead is one of the most widely used metals. It is used in some batteries, alloys, plastics, ammunition and radiation shielding. Lead used to be added to petrol to enhance its performance. As a result, vehicles emitted harmful lead compounds in their exhaust gases. Lead emissions from cars have fallen since fuel companies introduced unleaded petrol.

Up until the mid-1960s, lead was used to make some kinds of paint – for windows, doors and other woodwork as well as for some metal items, like radiators. Some older houses still have lead paint in them, which can be a health hazard.

Over time lead can build up in the central nervous system – this is the system that controls how our bodies work. At high levels it is like a poison that is particularly harmful to children and affects their mental development.
Lead in the air can be breathed into the body. It binds with red blood cells and gets distributed throughout the body. Lead poisoning can damage the brain. Lead can affect people’s health in other ways, such as causing abdominal pain, kidney damage and high blood pressure. It can also affect fertility.


Benzene is a VOC - volatile organic compound, 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 per cent of total emissions).

Possible chronic health effects associated with elevated benzene levels include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders and birth defects.

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.


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 (NOx). The sources of VOCs are similar to those described for NOx 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 NOx 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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