• Explain in brief the effects of environmental degradation in India .
Ans : One of the major effects of environmental degradation due to industrialization is the large-scale destruction of our forests, and this has a major impact on the productivity of our crop lands. The reduction of crop-land productivity due to the destruction of forests occurs in two ways. In the first place, when forests arc destroyed, there is a many-fold increases in the rate of soil erosion. The result is that the soil literally gets washed leading to an intensified cycle of floods and drought. Secondly, the destruction of forests leads to the shortage of firewood and this has an adverse impact on the productivity of crop lands. The reason is that when firewood becomes scarce, people begin to use cowdung and crop wastes as fuel for cooking and other purposes. As a result, every part of crop plants gets used (as fodder or fuel) and nothing goes back to the soil to enrich it. Over a period of time, this constant drain of nutrients from the soil adversely affects it productivity. The more intensive the agriculture (due to the use of high-yielding varities); without any manure and crop wastes going back into the soil, the faster is the nutrient drain. The district of Ludhiana in Punjab, for example, has the highest yield per hectare of many cereals today; but Ludhiana has also the highest deficiency of many micronutrients in its soil. In Punjab, many fanners have already started using zinc routinely as a fertilizer. If the dram of micronutrients from the soil continues, the farmers will soon be using sulphur, manganese and iron as fertilizers. The micronutrient fertilizer industry is likely to become a boom industry in the near future.
8.5 How is the ozone layer being destroyed? Explain in detail.
Ans: ln the stratosphere, the destruction (or depletion) of the ozone layer is mostly Caused by elemental chlorine a toms. The mechanism for this destruction of ozone involves the following two reactions:
O 3 + Cl ------------>ClO+O 2
ClO + O 3-----------> Cl 9+2O 2
Of course, there are some other chemical reactions going on in the stratosphere that modify and compete with the above two reactions. But if we ignore the other reactions and add the above two reactions, then we find that the net result is the following reaction:
2O 3 + Cl------------->3O 2 +Cl
Thus, in the presence of chlorine atoms (Cl), two ozone molecules are converted into three oxygen molecules, while there is no net consumption of Cl atoms, which merely act as a catalyst. As a result, one Cl atom can go on converting many ozone molecules (O 3 ) to ordinary oxygen molecules (O 2 ) before it is consumed by some other chemical reactions. It has been estimated that a single chlorine atom in the stratosphere can convert as many as 10 6 to 10 6 O 3 molecules to 0, molecules before being consumed by some other reactions. This mechanism is often referred to as the catalytic destruction of ozone since the chlorine atoms act as a catalyst for the reaction.
Most of the chlorine in the world is in the form of chemically stable sodium chloride (NaCI), either dissolved in the oceans or in underground salt deposits formed by the evaporation of ancient oceans. Elemental chlorine (Cl), which is a very reactive chemical, has a very short life-time in the lower atmosphere and has few natural ways to get from the lower atmosphere up to the ozone layer in the stratosphere. The only naturally occurring chemical that can transport much chlorine high enough into' the stratosphere to damage the ozone layer is methyl chloride (CH 3 CI), which is produced in large quantities by biological processes in shallow oceans. Most of this methyl chloride is destroyed in the troposphere (the lower atmosphere), but approximately 3% of the world-wide methyl chloride emissions reach the stratospheric ozone layer. Chemically active solar ultraviolet light in the range of 200 to 280 nm, which enters the ozone layer but does not penetrate below it, is strong enough to split up the methyl chloride molecules, releasing Cl atoms, which initiate the reactions given earlier and destroy the ozone molecules. Before we had the synthetic halogen compounds known as chlorofluorocarbons (CFCs), methyl was probably the main natural destroyer of the ozone layer. However, this destruction of the ozone was in balance with its natural production mechanisms, leading to a steady-state ozone layer.
Starting about a hundred years ago (i.e., from the first decade of the twentieth century), humans began releasing into the atmosphere synthetic chlorine-containing compounds in significant amount. The compounds like methyl chloride (CH 3 CI) that also contain hydrogen atoms can be attacked in the atmosphere by the OH radical. As a result, most of such chlorine- containing compounds do not survive long enough in the atmosphere to reach the stratosphere. Carbon tetrachloride (CCI,), on the other hand, has no hydrogen atom; so most of it is believed to reach the stratosphere and participate in the destruction of the ozone layer. The world production of carbon tetrachloride, however, has remained more or less constant over the last 70-80 years.
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