Environmental Issues Test - 73

The earth receives energy from the sun in the form UV (ultraviolet), visible, and near-IR (infrared) radiation, most of which passes through the atmosphere without being absorbed. Of the total amount of energy available at the top of the atmosphere, about 50% is absorbed at the earth's surface. Because it is warm, the surface radiates far IR thermal radiation, that consists of wavelengths that are predominantly much longer than the wavelengths that were absorbed. Most of this thermal radiation is absorbed by the atmosphere and re-radiated both upwards and downwards; that radiated downwards is absorbed by the earth's surface. This trapping of long-wavelength thermal radiation leads to a higher temperature than if the atmosphere were absent. The increase in the level of greenhouse gases has led to considerable heating of earth leading to global warming.

Greenhouse gases are the gases which contribute to global warming. Some of the primary greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. When the concentration of these gases increases in the atmosphere they form a layer which traps the solar radiation. Due to the trapped radiation, the temperature of the earth increases which leads to global warming. So the correct answer is option C.

Greenhouse gases are the gases which contribute to global warming. When the concentration of these gases increases in the atmosphere they form a layer which traps the solar radiation. Due to the trapped long wave infrared radiation, the temperature of the earth increases which leads to global warming. So the correct answer is option C.

Ozone gas can be traced in the stratosphere where they absorb the harmful ultraviolet radiation. The ozone layer is depleted due to the enhancement of chlorofluorocarbons (CFCs). CFCs find wide use as refrigerants. CFCs discharged in the lower part of atmosphere move upward and reach the stratosphere. In the stratosphere, UV rays act on them releasing Cl atoms. Cl degrades ozone releasing molecular oxygen. Cl atoms are not consumed in the reaction. 

Ozone depletion in the stratosphere has resulted in formation of a large area of thinned ozone layer, commonly called as the ozone hole. UV radiation of wavelengths shorter than UV-B, are almost completely absorbed by Earth's atmosphere, given that the ozone layer is intact. But, UV-B damages DNA and mutation may occur. It causes aging of skin, damage to skin cells and various types of skin cancers. In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of cornea, called as snow-blindness, cataract, etc. Such exposure may permanently damage the cornea. Thus, the correct answer is option D.

Radiation, that is given off by nuclear waste is extremely damaging to organisms, because it causes mutations at a very high rate. At high doses, nuclear radiation is lethal but at lower doses, it creates various disorders, the most frequent of all being cancer. Therefore, nuclear waste is an extremely potent pollutant. Heated (thermal) waste waters flowing out of electricity-generating units, e.g., thermal power plants, constitute another important category of pollutants. Thermal waste water eliminates or reduces the number of organisms sensitive to high temperature, and may damage the indigenous flora and fauna. Noise is an unwanted sound, or sound which produces unpleasant effects and discomfort on the ears. Sound becomes unwanted when it either interferes with normal activities such as sleeping, conversation, or disrupts or diminishes one's quality of life. All the three are pollutants but does not have any physical weight.  

Strontium-90 is found nearly everywhere in small amounts from past nuclear accidents and fallout from nuclear explosions. You can be exposed to low levels of Sr-90 by eating food, drinking water, or accidentally eating soil or dust, that contains Sr-90. Food and drinking water are the largest sources of exposure to Sr-90. Because of the nature of Sr-90, some of it gets into fish, vegetables, and livestock. Grain, leafy vegetables, and dairy products contribute the greatest percentage of dietary Sr-90 to humans. Everyone is exposed to small amounts of strontium-90, since it is widely dispersed in the environment and the food chain. 

Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. Domestic sewage primarily contains biodegradable organic matter, which readily decomposes by micro-organisms, which can multiply using these organic substances as substrates and hence utilise some of the components of sewage. It is possible to estimate the amount of biodegradable organic matter in sewage water by measuring biochemical oxygen demand (BOD). Micro-organisms involved in biodegradation of organic matter in the receiving water body consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. This causes mortality of fish and other aquatic creatures. 

Ozone depletion in the stratosphere has resulted in the formation of a large area of thinned ozone layer, commonly called as the ozone hole. UV radiation of wavelengths shorter than UV-B is almost completely absorbed by earth atmosphere, given that the ozone layer is intact. But, UV-B damages DNA and mutation may occur. It causes ageing of the skin, damage to skin cells and various types of skin cancers. In the human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of the cornea called as snow-blindness, cataract, etc. Such exposure may permanently damage the cornea.