Human contamination of the earth’s atmosphere can take many forms and has existed since humans first began to use fire for agriculture, heating, and cooking. Urban air pollution is commonly known as smog which is a smoky mixture of carbon monoxide and organic compounds from incomplete combustion (burning) of fossil fuels such as coal, and sulfur dioxide from impurities in the fuels. As the smog ages and reacts with oxygen, organic and sulfuric acids condense as droplets, hence increasing the haze. Examples of such types of air pollution include:
- In 1948, 19 people died and thousands were sickened by smog in the small U.S. steel mill town of Donora, Pennsylvania.
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In 1952, 2000 Londoners died of its effects.
Ozone Pollution
In many industrial countries, the levels of low-level ozone seem to be rising, and this form of pollution is becoming a serious environmental problem. As a pollutant, ozone is particularly harmful. At low concentrations, ozone can aggravate breathing difficulties and childhood asthma. At high concentrations, it seriously damages the lungs and harms the human immune system. Plants are also not spared from the harmful effects of low-level ozone, particularly so when ozone is mixed with other gases such as sulphur dioxide and oxides of nitrogen. Independent studies made by researchers show that ozone may play a major role in the damage done to vast tracts of forest, previously thought to be caused solely by acid rain. Controlled experiments show that ozone can have dire effects on trees. High concentrations of low-level ozone are found in photochemical smog.
Photochemical Smog
Photochemical smog is caused when certain oxides of nitrogen and hydrocarbons such as ethane, ethyne and propane come together in strong sunlight. In a series of photochemical reactions, the poisonous gas ozone is formed. The poisonous pollutants found in photochemical smog are known as photochemical oxidants and may include peroxylacetyl nitrate and aldehydes. Motor vehicles are a major cause of this type of smog.Sunlight causes the nitrogen oxides and hydrocarbons to combine and turn oxygen into chemical agent that attacks rubber, injures plants, and irritates lungs. The hydrocarbons are ozone, a oxidized into materials that condense and form a visible, pungent haze.
Acid Rain
Acid pollution continues to pose threat to lakes and forests throughout the world, despite attempts by many countries to introduce cleaner technologies. Acid pollution may come in the form of acid mist, fog and snow. However, the most widespread of acid pollution is acid rain. Acid rain is a secondary pollutant formed when acidic primary pollutants such as sulphur dioxide and nitrogen dioxide dissolve in the water vapour in the air and then fall as rain. Many of these polluting gases come from coal-fired power stations which burn large amounts of sulphur-containing coal and motor vehicles. Acid rain causes great damage to both the human and physical landscape. In the physical landscape, it has caused much damage to great buildings and monuments such as the Taj Mahal in India and the Parthenon in Greece. Lakes in Canada and Sweden have been badly affected by the burning of high-sulphur coal by the Polish industry as once the acidic polluting gases are air-borne, they can be carried over large distances by wind and air currents.
Global Warming
Indeed, global warming has been a much discussed issue over the past few decades. The main cause of it is actually the mass emissions of gases into the atmosphere from the burning of fossil fuels. It is difficult to stop the emission of these greenhouse gases as almost all activity in the industrialized society, such as transport and industrial production rely on the burning of fossil fuels. Greenhouse gases warm the Earth by retaining heat, through the reflection of long-wave radiation emitted from the Earth's surface. Carbon dioxide is perhaps the most important of all greenhouse gases, though other gases such as water vapour, methane, nitrogen oxides and chlorofluorocarbons (CFCs) play a part too. If the current rate of emissions of greenhouse gases through industrial activities is not reduced, global temperatures may rise by 3 degrees Celsius over the next 50 years.
The effects which are to follow this increase in global temperatures are well-known. The sea-level of the world may rise as a result of the melting of sea-based and land-based ice and glaciers. Low-lying islands such as the Maldives may be submerged by water and many coastal settlements will be wiped out. Much of the arable land near the sea would also rise. This would result in a reduction in the amount of food produced and there would be a world-wide food shortage. Though it has been widely argued that increased temperatures and increased levels of carbon dioxide in the air would increase plant growth, other weather conditions such as droughts and floods may destroy crops and more farmland. Moreover, the melting of land-based ice would result in the release of large amounts of methane, a powerful greenhouse gas which would again increase the rate of global warming.
Ozone Depletion
The ozone layer of the Earth actually consists of ozone spread over a considerable belt in the stratosphere, between 10 and 50 kilometres above sea level and is concentrated in at the upper level in the area that forms the ozone layer. The ozone layer absorbs 99% of the ultraviolet part of the solar rays, preventing them from reaching the Earth. These rays are damaging to all life and have been linked with skin cancer. The most damaging of all these rays are ultraviolet B rays.
The discovery of the depletion of the ozone layer was in 1974 when 2 American scientists found that CFCs can destroy ozone. Due to the stable nature of CFCs, they can remain in the atmosphere for many years. Eventually, they work their way up into the stratosphere and are decomposed by rays of ultraviolet light, thus releasing chlorine anions which destroy ozone through a catalytic reaction. 1 CFC molecule can destroy 10 000 molecules of ozone. In the Antarctic, the problem is particularly bad in winter, when spiralling air movements combine with very low temperatures to accelerate ozone depletion. The ozone hole appears when the concentration of chlorine reach 1.5 to 2.00 parts per billion.
The depletion of the ozone layer lets in more ultraviolet(UV) rays which can have an adverse effect on human, plant and animal life. It has been shown that a decrease of only 1% of tropospheric ozone could lead to a 3% rise in the number of skin cancers. Apart from cancer, UV light can also cause cataracts, snow-blindness, sunburn and ageing of the skin. It also lowers the resistance of the skin, making it susceptible to tumour growth.
