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... is converted into heat causing the emission of infrared radiation back to the atmosphere. Like glass in a greenhouse, these gases trap the infrared radiation preventing the heat to escape back into space, thus warming the atmosphere. This process is termed as Greenhouse effect. Carbon Dioxide (CO2), Methane (CH4), Nitrous Oxide (N2O) and Chlorofluorocarbons (CFCs) are some of the major green house gases that contribute in maintaining this process. However, human activities like burning fossil fuels, natural gas, coal, and oil to power industrial processes and motor vehicles have led to an increase in the level of green house gases in the atmosphere disturbing the critical balance .Its estimated that between 1900 and 1970, vehicle use rapidly expanded causing an emission increase of nitrogen oxide, from vehicle exhaust, by 690 percent. Carbon dioxide is the most significant of these gases and as a result of carbon dioxide emissions since the beginning of the Industrial Revolution 200 years ago; the atmosphere is now trapping more heat that would otherwise have escaped to space. Of all the greenhouse gases released by man-made processes, carbon dioxide is the largest individual contributor to the enhanced greenhouse effect, accounting for about 60% of the increase in heat trapping. Scientists predict that these increases in these gases in the atmosphere will lead to a global rise in temperatures and therefore lead to extreme climate changes, changes in rainfall patterns, a rise in the sea level and a wide range of impacts on plants, wildlife, and humans. Warmer temperatures are expected to partially melt the polar ice caps, leading to a projected sea level rise of twenty inches. A sea level rise of this magnitude would flood coastal cities, can cause landslides, storms and hurricanes. Diseases like malaria, which at present are primarily found in the tropics, may become more common in the temperate zones. The following graphs illustrate the relationship between increase of green house gases and rise in global temperatures: Increase in CO2 concentration 3 Increase in nitrous oxide concentration 4 Increase in global average surface temperature Carbon dioxide and nitrous oxide in the air have increased to about 370 parts per million, and are continuing to increase at a rate of about 1.2 parts per million each year leading to a rise in temperatures. OZONE DEPLETION At the stratospheric level, ozone forms a protective layer that filters out incoming radiation in the cell-damaging ultraviolet part (280 - 320nm) of the spectrum. Because of its protective function; the ozone layer is essential to life on earth. Among the several pollutants that attack the ozone layer, the most significant is Chlorofluorocarbons. Man-made Chlorofluorocarbons are the main cause of stratospheric ozone depletion. Chlorofluorocarbons or CFCs contain fluorine, carbon and chlorine atoms. Due to the inertness and water insolubility of CFCs; they are not destroyed nor are they dissolved in rainwater so they stay in the atmosphere for a very long time and diffuse up to the stratosphere where they come into contact with short wavelength ultraviolet radiation, which is able to split off chlorine atoms from the CFC molecules. CCl2F (g) u.v radiation---------------> CCl2F (g) + Cl (g) Cl (g) + O3 (g) -------------> ClO (g) + O2 (g) These chlorine molecules react with ozone breaking it down into ordinary oxygen molecules that do not absorb UV-B. Since ozone undergoes a photochemical decomposition producing oxygen atoms and molecules, there are significant numbers of oxygen atoms in the stratosphere, which leads to the regeneration of chlorine atoms in the stratosphere. So, 1 CFC molecule can destroy many ozone molecules. O3 (g) -------------> O2 (g) + O (g) ClO (g) + O (g) -------------> O2 (g) + Cl (g) Other pollutants such as nitrous oxide from fertilizers and the pesticide methyl bromide also attack atmospheric ozone. During the winter months in Antarctica when the region receives no sunlight, the stratosphere forms Polar Stratospheric Clouds (PSCs). These PSCs provide an ideal catalytic surface on which chlorine and bromine can react with the ozone, thus destroying the layer. This is known as the “Ozone hole”. Depleted ozone layer would allow more of the Sun's rays to reach Earth's surface. An increase in the levels of UV reaching the Earth as a result of ozone depletion may result in several adverse effects such as skin cancer, and severe damage to the immune system. According to estimates a 10% global loss of ozone may lead to a 26% increase in the incidence of skin cancers among fair skinned people. ACID RAIN Acid rain is one of the most serious threats to the environment. Acid rain is a widespread term used to describe all forms of acid precipitation rain, snow, hail and fog. When atmospheric pollutants such as sulphur dioxide and nitrogen oxides mix with water vapor in the air, they are converted to sulphuric and nitric acids. These acids make the rain acidic, hence the term "acid rain”. SO2 + H20 + H20 H 2SO4 sulphuric acid NO2 + H20 + H2O HNO3 > nitric acid Acid rain disrupts aquatic ecosystems such as rivers, lakes and wetlands, affecting fish and amphibians, destroys forests, lead to soil erosion, and corrodes statues and buildings. Acid rain can harm vegetation and run into lakes and rivers, which changes the chemistry of the water; makes it potentially uninhabitable for aquatic animals, burns the leaves of plants and acid deposition erodes precious artifacts, including the Parthenon temple in Athens, Greece, and the Taj Mahal in Agra, India. The major health concerns associated with exposure to high concentrations of sulphur dioxide include Asthma, bronchitis and emphysema. THERMAL INVERSION A thermal inversion is a condition in which the temperature of the atmosphere increases with altitude in contrast to the normal decrease with altitude. When thermal inversion occurs, cold air underlies warmer air at higher altitudes the warm air produces a thermal lid to trap the pollutants. In 1948 a thermal inversion occurred in Pennsylvania; Over 40% of the citizens became ill with respiratory problems and severe headaches. Other harmful pollutants Another very harmful air pollutant is Carbon monoxide. CO is produced by the incomplete combustion of carbon-based fuels, including gasoline, oil, and wood. CO molecules can enter the bloodstream, where they attach themselves to the hemoglobin cells and this leads to suffocation. Lead is another highly toxic metal that can cause nervous system damage and digestive problems, and some lead-containing chemicals cause cancer and can also harm wildlife. Ozone in the stratosphere protects us from the dangerous ultraviolet rays. However, at ground level where it is a pollutant, it damages human health, the environment, and crops. It can irritate the respiratory tract; cause chest pain, persistent cough, and can lead to lung infection. Volatile organic compounds like benzene, formaldehyde...