Sources of air pollution and their risks
Air pollution occurs when a substance is present in the air in quantities that can have adverse effects on people's health and on the surrounding environment.
This page describes the main air pollutants of concern in the UK. For further detail, the UK National Air Quality Information Archive discusses the main causes of air pollution and the health effects of each of the main pollutants, while the Department of Health website also provides access to health-related information.
Nitrogen Dioxide (NO2)
Nitrogen dioxide is formed through the high temperature burning of fuel, principally from road traffic. This means that concentrations are greatest in urban areas where traffic levels are the highest. Other significant sources are power plants, heating plants and industrial processes.
Nitrogen dioxide can potentially impact on health by irritating the lungs and lowering resistance to respiratory infections. It can also lead to ozone formation by reacting with VOCs in sunlight, and ozone can irritate the airways of the lungs and impair lung function.
There are also environmental consequences of nitrogen dioxide formation. Acid deposition can occur as a result of the conversion of nitrogen dioxide to nitric acid in the atmosphere, which then falls to the ground as "acid rain" for instance. Acid rain can cause damage to forests and freshwater lakes. Because nitrogen dioxide has a role in ozone formation, it indirectly contributes to the effects of ozone pollution, which include a reduction in crop yields and damage to trees.
Particulate Matter (PM10)
Particulate matter refers to very small solid and liquid particles present in the atmosphere. The principal source of particulate matter in the UK is road traffic emissions, particularly from diesel vehicles. Particulates are also released as a result of industrial processes and have natural sources such as dust storms and volcanoes.
PM10 refers to fine particles with a diameter of less than 10 micrometres (µm). These particles are of particular concern for health as they can be carried deep into the lungs where they can cause inflammation and worsening of lung and heart conditions. Particulates may also carry surface-absorbed carcinogenic (cancer-causing) compounds into the lungs.
Sulphur Dioxide (SO2)
Sulphur dioxide is an acidic gas which combines with water vapour in the atmosphere to produce acid rain. The principal source of sulphur dioxide is power stations burning fossil fuels containing sulphur. Significant problems now only tend to occur in cities where coal is still widely used in domestic heating, industry and power stations. Thus, sulphur dioxide pollution is not a major problem in most cities in the UK.
Health effects of sulphur dioxide include a reduction in lung function in asthmatics, while tightness of the chest and coughing occur at high levels.
Both dry deposition and wet deposition as sulphuric acid ("acid rain") have environmental effects. Such effects include freshwater acidification, damage and destruction of vegetation, degradation of soils and damage to historic monuments and buildings
Carbon Monoxide (CO)
Carbon monoxide is formed when fuels containing carbon are burned without enough oxygen present, or when they are burned at too high a temperature. It is produced almost entirely from road traffic emissions in European urban areas.
By preventing the normal transport of oxygen by the blood, carbon monoxide leads to a reduction in the supply of oxygen to the heart, particularly in people suffering from heart disease.
Lead
Sources of lead include fossil fuel combustion, metal processing industries, waste incineration and the manufacture of batteries. Lead is also used as an additive in petrol but increased use of unleaded petrol has meant a decline in recent years.
Lead can be harmful in small amounts, especially to young children and infants. Exposure to lead has been associated with impaired mental function and neurological damage in children.
Volatile Organic Compounds (VOCs)
Volatile Organic Compounds are organic chemicals that easily vaporise at room temperature. The group of VOCs known as hydrocarbons include benzene and 1,3-butadiene. The main sources of benzene in Europe are the distribution and combustion of petrol. The principal source of 1,3-butadiene is from fuel combustion of petrol and diesel vehicles, and a further source is industrial processes such as the manufacture of synthetic rubber.
Some VOCs can be quite harmful to human health, potentially contributing to central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects. Both benzene and 1,3-butadiene are known carcinogens (cancer-causing agents).
Ozone (O3)
In the upper atmosphere or stratosphere, the presence of ozone is necessary in order to protect the earth from harmful ultraviolet radiation. However, at ground level (in the troposphere), ozone can have harmful effects on both humans and the environment. Ozone can irritate the airways of the lungs and impair lung function, and asthmatics may be more sensitive to such effects. Vegetation effects include a reduction in crop yields and damage to trees.
Ozone is a secondary pollutant formed in the presence of sunlight by the reaction of VOCs (volatile organic compounds) such as benzene and 1,3-butadiene with nitrogen oxides (nitrogen dioxide and nitric oxide). There are no direct man-made sources of ozone but people indirectly influence ozone levels through fossil fuel combustion, industrial processes and solvent usage for instance. Traffic emissions of nitrogen dioxide and VOCs will also indirectly influence ozone levels.