Current Global Environmental Issues Unit-4

Green House Effect The Increase in CO 2 content of the environment has been responsible for gradual heating up the globe, by a process called as green house effect. The progressive warming up of the earth’s surface due to blanketing effect of manmade CO 2 in the atmosphere is known as green house effect.

Green House Effect

From sun 3 types of radiations are emitted, ultraviolet rays(< 400 nm), Visible rays( 400 – 700 nm) and Infrared rays (700 – 1000 nm), of this the visible rays are having maximum intensity i.e. (400 nm to 700nm wavelength). Approx 47 % of the solar radiation is absorbed by water and land surfaces and the remaining rays are radiated back to the atmosphere in the form of Infrared rays (700 nm – 1000 nm). Water vapor and CO2 molecules in atmosphere near earth’s surface absorb the infrared radiations (heat rays) emitted by earth. Thus the net effect causes warming of atmosphere. This effect is called a green house effect.

Principle of Green house effect The transparent walls and roofs of the green house are such that they allow visible sunlight to enter but prevents the entry of long wavelength Infrared radiations to go out. Thus the sunlight is absorbed by soil and structure of the green house. It is then re-emitted as heat rays which cannot pass through the glass. The amount of energy in the green house thus increases the warmth of the atmosphere. In similar ways the earth’s atmosphere bottles up the energy of the sun like green house. Here CO 2 and water vapor acts like glass windows. CO 2 and water vapor in the atmosphere transmits short wavelength solar radiations but reflect longer wavelength heat radiations from warm surfaces of the earth. CO 2 molecules are transparent to sunlight but not to heat radiations, so they trap and re-enforce the solar heat like a green house

Green House

Green house Gases Carbon dioxide ( CO 2 ) Methane ( CH 4 ) Nitrous oxide ( N 2 O) Chlorofluorocarbon (CFC) Ozone

Sources of Green House Gasses 1) Burning of Coal, Oil, Natural Gas in the factories. 2) Burning of fossil fuels at power stations 3) Use of Petrol and Diesel from automobiles, railways, aircrafts etc. 4) Burning of firewood and deforestation 5) Tree and plants release carbon as CO 2. 6)Fire in the forests contribute to the release of CO 2

Effects of Warming up of Air:- Increase in temperature on earth’s surface will cause more evaporation of surface water. Melting of Glaciers (ice mountains) Rise in Sea Level will wash away entire countries from Bombay to Boston. Shifting of climate zones will occur.

CO 2, CH 4, N 2 O, CFC’s, O 3, H 2 O vapor

Control Reduce the consumption of fossil fuels Use anti pollution devices Non conventional energy sources should be developed as a alternate to fossil fuel. Prevent deforestation Planting more trees.

Acid Rain Acid Rain is a environmental Problem caused due to rapid industrialization. Acid rain has become invisible threat to rivers, lakes and forests. Acid rain means presence of acids in rainwater. The basic component of acid rain are nitric acid, and sulphuric acid.

Causes of Acid Rain Acid Rain is because of human activities. Sulphuric acid is formed when (SO 2 ) is discharged from combustion process converts to sulphurtrioxide (SO 3 ) which reacts with the water vapor present in the atmosphere to form sulphuric acid (H 2 SO 4 ). – The oxides of sulphur and nitrogen are produced by combination of fossil fuels, smelters, power plant, automobile exhausts, domestic fire.

Acid Rain formation

Effects of Acid Rain The acid rain damages the leaves of plants and trees and retard the growth of forest. Wash out the nutrients from the soil. Significant reduction of fish population and decease in aquatic micro organisms. Damage to Buildings and structural materials. Corrosion of houses, monuments, statues and bridges. The human nervous system, respiratory system and digestive system may get affected Acid rain reduces the rate of photosynthesis and hence growth of plants.

Control Liming of Lakes Tough laws to reduce acid forming pollutants, being released in atmosphere.

Ozone Layer Depletion Ozone layer depletion is mainly due to Chloro-floro carbons (CFC). Ozone layer prevents the harmful ultraviolet rays from entering in the atmosphere but (CFC) is one of the main ozone eaters and it allows the penetration of harmful ultraviolet rays. Chloro-floro carbon remains in the atmosphere for decades and reacts with the atmospheric chlorine to accelerate the long chain reaction. This chain reaction slowly eats away the oxygen atom which could be used in the formation of ozone. © NOAANOAA

Thus it leads to decrease in Ozone concentration which results in reaching of ultraviolet rays to earth surface due to which heat increases to uncomfortable levels and the temperature of earth increases.

Main Ozone layer Depletors CFC (Chloro Floro Carbon) The Chlorofloro carbon are less costly, non toxic, and safe to handle material is used in propellants, cleaning solvents, plastic foams, in dry cleaning industries, for sterilizing surgical instruments. Because of wide use of CFC the CFC in the atmosphere is increased and which has caused irreparable damage to our environment.

Oxides of Nitrogen:- Burning of Fossil fuels and increase in use of nitrogen as a fertilizer are also contributing in destruction of ozone layer. Thus in addition to CFC, the oxides of nitrogen also plays an important role in depletion of Ozone.

Mechanism of Ozone depletion The chlorofloro carbons are highly stable and hence they slowly diffuse in the atmosphere. The ultraviolet rays decompose the CFCs and thus free chlorine and fluorine radicals are released In the atmosphere. This chlorine radical released in the atmosphere converts O 3 into O 2 Similarly oxides of Nitrogen also depletes the ozone

CFCl 3 CFCL 2 + Cl Cl + O 3 ClO + O 2 ClO + O Cl + O 2 Similarly NOx + O 3 NO 2 + O 2 UV rays

Oxygen in the Atmosphere UV radiation + O2O2 O O + O + O2O2 O 3 (ozone)

UV O 3 (ozone) O + O2O2 O + O2O2 O2O2 + O + O2O2 + heat +

Cl - “Free Radicals”… Cl - “free radical” O 3 ( ozone ) + O2O2 ClO + + O Cl - “free radical” + O2O2

Effects of Ozone Depletion The damage to ozone layer will result in damage to plants and animals For every 2.5 cm increase in the size of ozone hole, there will be 5 – 6 % increase in skin cancer and cataracts. Ultraviolet rays may interfere with photosynthesis leading to lower crop yield Ultraviolet rays causes genetic changes in DNA, leading to lower crop yield.

Control. Discourage use of CFCs and NOx Better alternative for CFC should be developed. Reforestation and forest prevention.

© NASANASA 28.0 million km2 on 25 September 2006

maximum ozone hole area for 2009 was 24 million km 2 on 17 September.17 September The Dobson unit (DU) is a unit of measurement of atmospheric ozone columnar density, specifically ozone in the stratospheric ozone layer. One Dobson unit refers to a layer of ozone that would be 10 µm (micrometre)atmosphericozonecolumnar densitystratosphericozone layermicrometre

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