Ozone layer Depletion- A brief Summaryby Deepak Subedi | 08-09-2018 17:11 |
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       What is Atmosphere? An atmosphere (from Greek ἀ??ός (atmos), meaning 'vapour', and ???ῖ?? (sphaira), meaning 'sphere') is a layer or a set of layers of gases surrounding a planet or other material body, that is held in place by the gravity of that body. Earth's atmosphere can be divided (called atmospheric stratification) into five main layers. Excluding the exosphere, the atmosphere has four primary layers, which are the troposphere, stratosphere, mesosphere, and thermosphere. A layer in the earth's stratosphere at an altitude of about 10 km (6.2 miles) containing a high concentration of ozone, which absorbs most of the ultraviolet radiation reaching the earth from the sun. Ozone Layer Depletion Ozone depletion describes two related events observed since the late 1970s : a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions.[1] The latter phenomenon is referred to as the ozone hole. There are also springtime polar troposphere ozone depletion events in addition to these stratospheric events. There are many Substances such as CFCs, and others that are cited, that lower the ozone layer do not directly destroy ozone. First they undergo photolysis, forming hydrogen chloride (HCl) or chlorine nitrate (ClONO2), molecules that do not react with ozone directly, but slowly decompose, giving, among other things, a small number of chlorine atoms (Cl) and Of chlorine monoxide (ClO) molecules that catalyze the destruction of ozone. The reactions involved in the processes of destruction are more than 100, but can be simplified in the following: Cl + O 3 —–> ClO + O 2 ClO + O —–> Cl + O 2 Net effect: O 3 + O —–> 2 O 2 The chlorine atom acts as a catalyst, ie it is not consumed in the reaction, so it destroys thousands of ozone molecules before disappearing. The bromine atom is even more destructive than chlorine (about 10 or 100 times more). On the other hand, along with this, the chlorine concentrations are very low in the stratosphere and the bromine concentrations are even lower. Compounds that causes ozone layer depletion Chlorofluorocarbons (CFCs) They are compounds formed by chlorine, fluorine and carbon. They are often used as refrigerants, solvents, and for the manufacture of spongy plastics. The most common are CFC-11, CFC-12, CFC-113, CFC-114, and CFC-115 which respectively have an ozone depletion potential of 1, 1, 0.8, 1, and 0.6. Chlorofluocarbons, the chemicals used as the propellant for aerosol cans and Bromofluocarbons, Halon, are destroying the earth?s Ozone layer. These chemicals were used in Freon and for fighting fires. Manufactures thought the chemicals were inert and not harmful to the environment. When the chemicals reached the earth?s stratosphere, they reacted with Ultraviolet radiation, which caused them to break down and release Chlorine and Bromine into the earth?s ozone layer. The Ozone layer protects the earth from UV-B Rays. The chemicals caused a reaction, which made the ozone layer break down into pure oxygen. The layer lost its shielding effect from the suns UV rays. The Bromine and Chlorine kept interacting with the ozone molecules until they eventually left the ozone layer to bond with other compounds Hydrochlorofluorocarbons (HCFCs) Compounds formed by H, Cl, F and C. They are being used as substitutes for CFCs because many of their properties are similar and are less harmful to ozone by having a shorter half-life and releasing fewer Cl atoms. Decreases are between 0.01 and 0.1. But as they remain harmful to the ozone layer, they are considered only a temporary solution and their use has been banned in developed countries since the year 1930. Halons They are compounds formed by Br, F and C. Because of their ability to put out fires are used in fire extinguishers, although their manufacture and use is prohibited in many countries because of their ozone-depleting action. Their ability to harm the ozone layer is very high because they contain Br which is a much more effective atom destroying ozone than the Cl. Thus, halon 1301 and halon 1211 have ozone depletion potentials of 13 and 4 respectively. Methyl bromide (CH3Br) It is a very effective pesticide that is used to fumigate soils and in many crops. Given its content in Br damages the ozone layer and has an ozone depletion potential of 0.6. Carbon tetra-chloride (CCl4) It is a compound that has been widely used as a raw material in many industries, for example, to manufacture CFCs and as a solvent. It was no longer used as a solvent when it was found to be carcinogenic. It is also used as catalysts in certain processes where chlorine ions need to be released. Its ozone depletion potential is 1.2 Effect of ozone layer depletion Ozone layer depletion can have some serious consequences on effects of human health, plants, marine ecosystems, biochemical cycles and earth?s environment. Effect on health of humans With depletion in ozone?s layer, we humans are more prone to UV rays that reaches the Earth?s surface. Studies suggests that high levels of UV Rays cause non-melanoma skin cancer and plays a major role in malignant melanoma development. Direct exposure to UV rays can lead to development of cataracts which clouds the eye?s lens. Permanent exposure to UV rays can also lead to weakening of the response of immune system and even permanent damage to immune system in some cases. Aging of skin is yet another problem that will make you look older than what you really are. Extensive exposure to UV rays can lead to acceleration of the aging process of your skin. Effect on plants Plants become another casualty by radiation effects of UV rays. The physiological and developmental processes of plants are also severely affected apart from the growth. Some other changes that are caused by UV inlcude the way plants form, timing of development and growth, how nutrients are distributied within the plant and metabolism, etc. Effect on marine ecosystems UV rays also have adverse effect on the marine ecosystems. It badly affects the planktons that form the foundation of aquatic food webs. Phytoplankton grow close to the surface of the water and plays vital role in the food chain and oceanic carbon cycle. Changes in UV levels is know to affect both orientation and motility in phytoplankton. This reduces the survival and growth rate of these organisms. UV rays are also known to affect the development stages of fish, shrimp, crab, amphibians, and other marine animals. When this happens it affects whole marine food chain as animals in the upper food chain that feed on these fishes are also affected. Effect on biogeochemical cycles Increases in UV radiation alters both sources and sinks of greenhouse gasses in the biosphere e.g.: e.g., carbon dioxide, carbon monoxide, carbonyl sulfide, ozone, and possibly other gases. Changes in UV levels would contribute to biosphere-atmosphere feedbacks that mitigate or amplify the atmospheric concentrations of these gases. Solutions to Ozone Layer Depletion Depletion to ozone layer depletion does not affect a region or a country. In fact whole world is vulnerable to its after affects. The increase in the levels of UV rays lead to high rate of skin cancer and eye related problems. Lets have a look at some of the solutions to ozone layer depletion. 1. Avoid products that results in ozone depletion 2. Advocate for ozone protection 3. Speak to your family, friends, colleagues Replace halon-based fire extinguishers with others using foam. Check on the label of the products, which we buy at the supermarket, to report that they do not damage the ozone layer. Use your car only when necessary. The less we use our cars, the less pollutants we will emit into the atmosphere. Remember that burning fossil fuels breeds many substances that damage the ozone layer Do not buy refrigerators or air conditioner equipment that use CFCs as refrigerant. Look for this information in the labels, or ask the supplier of the product directly. Do not use cleaning solvents containing CFCs or ammonia. Do not use sprays, and do not buy objects made of plastic foam (dry ice or freezer). If you receive these products as a fill of your mail packages, return them immediately to the sender. Low consumption of these products will discourage plastic foam manufacturer. Source: Internet Note: Go through each images from below to above to have clear concept of ozone layer depletion. |
