The Effects of Halogens on the Ozone Layer

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This essay aims to describe the impact of halogenated species on the tropospheric ozone (O3). Halogenated species are in the focus of this study because they are involved in the ozone destruction in the atmosphere. Despite the relatively small concentrations of halogenated species in the atmosphere, their potential to destruct the ozone is very high due to their catalytic mechanism of ozone depletion that regenerates halogenated species making them available to react further with the ozone. The word halogen means ‘salt former’, and compounds that contain halogens are called salts. The halogens are diatomic, monovalent elements from Group VII of the periodic table comprising of Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At). The halogens are the only group in the periodic table that contain elements in the three common states of matter at standard temperature and pressure. Figure 1 Ozone is a reactive oxidant gas produced naturally in trace amounts in the Earth’s atmosphere. In the troposphere it is formed by photochemical reactions in the presence of so called precursors such as CO and volatile organic compounds. In the stratosphere it is formed mainly by the reaction of molecular oxygen and atomic oxygen, the latter of which is a product of O2 photolysis. Figure 2 Halogens including Chorine, Bromine and Iodine are very reactive when injected into the atmosphere mostly as organic compounds named Halocarbons or Organohalogens. Bromine, however, being the more reactive than chlorine. Over the years, studies on the ozone layer have been conducted and have been observed that the depletion of the ozone layer is mainly due to the release of these chemical substances (halogens) into the atmosphere. As the percentage of ozone in the atmosphere decreases, the amount of UV radiation reaching the surface increases. It is the UV radiation,

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