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Chapter: 11th 12th std standard Geography earth space Higher secondary school College Notes

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Ozone - Depleting Substances and Urban heat islands

A family of compounds known as chlorofluorocarbons (CFCs) have the most significant effect on the ozone layer. CFCs contain different proportions of three elements. carbon (C), fluorine (F) and chlorine (c1). CFCs where produced and used extensively as refrigerants starting in the early 1930's after a scientist named Medgley discovered this gas. At that time, ammonia and sulfur dioxide were widely used as refrigerants. But ammonia was undesirable because it is a strong eye and respiratory irritant.

Ozone - Depleting Substances

 

A family of compounds known as chlorofluorocarbons (CFCs) have the most significant effect on the ozone layer. CFCs contain different proportions of three elements. carbon (C), fluorine (F) and chlorine (c1). CFCs where produced and used extensively as refrigerants starting in the early 1930's after a scientist named Medgley discovered this gas. At that time, ammonia and sulfur dioxide were widely used as refrigerants. But ammonia was undesirable because it is a strong eye and respiratory irritant. Chlorofluorocarbons were seen then as the ideal compounds because they were thought to be harmless. They are chemical inert, non-toxic, and insoluble in water.

 

For the past seventy years, CFCs were used extensively in aerosols, refrigerants, and foams. Because of their non-reactive nature. CFSs are able to rise undisturbed into the atmosphere. When CFSs migrate high enough and are hit by enough ultraviolet radiation, they are broken down and release chlorine atoms. The chlorine atoms react with O3 gas and make ozone molecules unavailable. One chlorine atom can destroy over 100,00 molecules of ozone.

 

On our planet, a temperature balance in nature is necessary to sustain living organisms. This balance occurs due to the absorption of short wave (visible) solar radiation by surfaces on the earth, and the subsequent transformation of that radiation into longer-wave infrared. Infrared is then absorbed and 'trapped' by carbon dioxide, causing the troposphere to maintain a significantly warmer temperature.

 

Since the Industrial Revolution, there has been a high rate of increase in the concentration of carbon dioxide. This gas have risen by 30% since the late 1800s. Furthermore, scientists predict that CO2 concentrations will continue to rise, likely reaching 2 to 3 times the pre-industrial level by 2100. The carbon dioxide effect can become a problem when the amount of heat-absorbing gases in the atmosphere rapidly rises far above the levels at present.

 

The warming of atmosphere is seen not only at global level but also at local levels. Local-Urban heat islands are one such example. 'Urban heat islands' are a kind of localized enhanced warming phenomenon. They are simply built-up areas of a city that are significantly warmer than the surrounding area of country side.

 

Urban heat islands : The difference in temperature comes from the fact that buildings, paved surfaces, and other human-made structures absorb higher amounts of sunlight than most natural objects. This energy is re-radiated at longer wavelengths during the night. The atmospheric pollution in the form of carbon dioxide, a heat-absorbing gas, forms a 'local' atmosphere, trapping in the heat.

 

Meteorologists have noticed that metropolitan areas are creating their own weather patterns at night due to the collision of cool air from the surrounding area with the warmer city air. It is important to note that urban heat islands are a localized effect, whereas the general atmospheric effect is global in extent. So far we have examined the atmospheric phenomena and found that the current state of the atmosphere is the result of increased industrial activities. In the last century especially, the atmospheric system that evolved over billions of years has been subject to rapid changes.

James Lovelock, author of Gaia, proposes that the atmosphere owes its current composition to living systems. He remarks that life on Earth requires a particular atmospheric composition, and this composition is in turn maintained by the interactions between biological systems and the atmospheric system.

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