Urban Air Pollution Causes Effects and Solutions
Air pollution is a major issue in the developed and developing worlds. It has potentially serious effects on human health, especially in an urban context where there is a high population density and a consequently large number of polluting sites. ... Of the molecular pollutants carbon dioxide (CO2) is the most common by-product of combustion but is not usually considered a pollutant, in the context of urban air pollution, as it is naturally present in the atmosphere. ... Sulphur dioxide (SO2) originates when sulphur compounds or materials containing sulphur are burnt, and oxides of nitrogen (both NO and NO2, collectively known as NOx) are formed by most combustion in air. ... The fundamental cause of pollution is the need for energy. The UN estimates that by 2000 AD urban areas will contain 47% of the worlds population [1]. ... Within the urban environment the greatest sources of pollution are transport and industry, with domestic sources contributing least. ... CO is most commonly formed by burning hydrocarbons without sufficient oxygen, a situation which easily occurs in internal combustion engines, for instance when the fuel-air mixture is too rich or the engine is not timed correctly. ... This was a result of three main factors: the reduction in the number of power stations in London from fifteen to three [4]; a general decline in heavy industries which contribute to SO2 pollution, e. ... smelting; and the reduction in domestic coal use since the introduction of the Clean Air Act 1956. ... In air NO will slowly oxidise to NO2, so that at low concentrations NO will predominate. Oxides of nitrogen can react with hydrocarbons in the air, or they can dissolve in water to produces nitric or nitrous acids. ... Ozone can remain in the lower atmosphere for periods of several days given the right conditions and London Scientific Services proposes [8] that as a result the ozone levels in London could be raised when polluted air from European industrial sources moves over London. ... Asbestos is a known carcinogen, which can be released into the urban atmosphere by improper building or demolition procedures. ... So we now turn to the effects of the major pollutants in the urban context. One point that is made in almost every work of reference is that the effects of pollutants are synergistic - for instance, in asthmatics the presence of O3 in the air can increase the effect of SO2 on the lungs [13]. Concentrations of pollutants are given throughout as mass ratios, in parts per million or parts per billion (ppm or ppb), of pollutant to air [14]. ... In addition to actual pollution emissions, prevailing meteorological conditions can greatly influence the concentrations found at ground level, especially wind speed and the presence of a temperature inversion. ... Temperature inversions form when the air close to the ground is cooler than air higher up and as a result there is little vertical motion of the air, so pollutants are trapped close to the ground and their concentrations can build up. ... This occurs in the environment as acid rain, but inside the body the acid causes irritation to the throat and upper passages in the lungs. ... For comparison the WHO pollution guidelines are 122ppb averaged over 1 hour, and 35-52ppb averaged over 1 day. ... SO2 has also been linked to increased mortality from heart attacks as a result of severe pollution incidents, in New York [17], Paris [18] and London [19]. ... Many plants and trees are adversely affected by acid conditions so vegetation grows less well in towns, with possible consequences for the urban microclimate. Of the oxides of nitrogen NO is relatively harmless but nitrogen dioxide can have serious health effects. ... Pollution episodes where hourly concentrations of NOx are at or above the 105ppb guideline have been associated with an increased incidence of acute asthma symptoms, but such concentrations are infrequent in the UK [22].