5.6 Ozone Depletion By: Aditi

5.6.1 Outline the overall structure and composition of the atmosphere Found in two layers of the atmosphere: the troposphere (considered good) and stratosphere (where it is considered bad). In the troposphere it is considered a pollutant and a danger to human life. In the stratosphere it blocks incoming ultraviolet radiation from the sun and protects life from damaging UV radiation. It is a chemical made up of three oxygen molecules, O3.

5.6.2 Describe the role of ozone in the absorption of ultraviolet radiation Ozone present in the stratosphere protects life from incoming UV radiation. UV radiation is absorbed during the process of formation and destruction of ozone and oxygen. This is an example of a dynamic equilibrium as oxygen and ozone are continuously breaking down and reforming. Under the influence of UV radiation oxygen breaks down into oxygen atoms. Most notably in humans UV radiation causes skin cancer.

The absorption of UV radiation by ozone is crucial as UV radiation has a number of damaging effects: mutation and effects on health; damage to photosynthetic organisms especially phytoplankton. Most notably in humans UV radiation causes skin cancer.

5.6.3 Explain the interaction between ozone and halogenated organic gases Halogenated organic gases are stable under normal conditions but can liberate halogen atoms when exposed to ultraviolet radiation in the stratosphere The atoms react with monatomic oxygen and slow the rate of ozone re-formation. Pollutants enhance the destruction of ozone, thereby distributing the ozone production system. Ozone depletion is the result of air pollution. The most important ozone-depleting gases are the chlorofluorocarbons or CFCs. Others include HCFCs (hydrochlorofluorocarbons), halons (fire extinguishers which release bromine atoms), and methyl bromide (pesticides which release bromine atoms).

5.6.4 State the effects of ultraviolet radiation on living tissues Mutation and subsequent effects on health and damage to photosynthetic organisms, especially phytoplankton. The effects of UV-B radiation on human skin are varied and widespread. UV-B induces skin cancer by causing mutation in DNA and suppressing certain activities of the immune system. The United Nations Environment Program estimates that a sustained 1 percent depletion of ozone will ultimately lead to a 2-3 percent increase in the incidence of non-melanoma skin cancer. With regard to plants, UV-B impairs photosynthesis in many species. Overexposure to UV-B impairs the productivity of phytoplankton in aquatic ecosystems.

5.6.5 Describe three methods of reducing the manufacture and release of ozone-depleting substances Replace CFCs with Carbon dioxide, propane or air as a propellant Replace aerosol propellants Recover and recycle CFCs from refrigerators and air-conditioning units Create legislature to have fridges returned to manufacturers

5.6.6 Describe and evaluate the role of national and international organisations in reducing the emissions of ozone depleting substances. UNEP (United Nations Environment Programme), forges international agreements, studies the effectiveness of these agreements, and the difficulties implementing and enforcing them. the Montreal Protocol (1987), which is an international agreement on reduction of emission of ozone-depleting substances. The signatories agreed to freeze production of many CFCs and halons and strongly reduce consumption and production of these substances by 2000. Most countries followed the rules but China and India continued to produce and use huge amounts of CFCs. But they have since both agreed to phase out the use of CFCs.

Thank you for your attention!