Concentrations ofsix pollutants reduced between 2007 and 2008. Between 1998 and 2008 concentrations of eight pollutants have reduced.
The substances that cause air pollution are called pollutants. If they are pumped into our atmosphere and directly pollute the air are called primary pollutants. Carbon monoxide from car exhausts, sulphur dioxide from the combustion of coal is example for primary pollutants. If primary pollutants in the atmosphere undergo chemical reaction, and further cause pollution, they are secondary pollutants. Photochemical smog is an example for secondary pollutant.
Air pollutants mainly occur as a result of gaseous discharges from industry and motor vehicles. There are also natural sources such as wind-blown dust and smoke from fires. With increasing urbanisation and industrialisation, more pollution has been added to the air by industrial, commercial and domestic sources. When these concentrated gases like Co, Co2, So2, No2, Ozone, and Pm10 exceed safe limits, we have a pollution problem.
Air pollution, particularly in cities, is not a new problem. Back in the middle ages the use of coal in cities such as London was beginning to escalate. In UK the industrial revolution during the 18th and 19th centuries was based on the use of coal. Urban air pollution levels often reached very high levels due to the burning of coal in industries, as well as in homes for domestic heat.
During foggy conditions, pollution levels escalated and urban smogs (smoke and fog) were formed. These often brought cities to a halt while disrupting traffic, and may also cause deaths. Effects of air pollution on buildings and vegetation also became obvious.
Inhaling So2 in excess amount would lead to cough, tightening of chest, and irritation of lungs. NO2 results in irritation and inflammation of lungs. PM10 may cause inflammation of lungs, linkage of long term exposure to coronary heart disease and lung cancer. Intake of carbon monoxide in excess amount would leads to prevention of normal transport of oxygen by blood, resulting in the reduction of oxygen supply to the heart. Ozone causes pain on deep breathing, cough, irritation and inflammation of lungs. Benzene and 1, 3-butadiene leads to cancer. Lead is responsible for linkage of exposure to impaired mental function and neurological damage in children. In the great 'smog disaster' in London in 1952, nearly 4,000 people died in a few days due to the high concentrations of pollution.
Air pollution in London is decreasing
1. Days of moderate-high, and very high air pollution at selected urban sites across London during 2000-2008 (Source: Defra).
2. Relative annual mean concentrations of SO2, PM10, Nox and NO2 monitored at several sites across London. (Source: London Air Quality Network, King's college London).
According to the data, there has been a downward trend in the annual mean concentration of SO2. Since 2000 it had fallen significantly. By the spring of 2009 it had fallen by 80% since November 1996. Annual mean concentration of PM10 has decreased by nearly 26 % between November 1996 and late 2008. The concentration of NO2 has fallen since 2000, and now appears to