Ozone Layer Flashcards
Ozone layer
The ozone layer is a fragile shield of gas that protects Earth from harmful ultraviolet radiation of the sun. It contains high concentration of ozone, or O3, in relation to other parts of the atmosphere. The atmosphere is divided into several layers. The lowest region is the troposphere, which extends up to 10 km. The next layer is the stratosphere, which continues from 10 km to about 50 km. The ozone layer here is about 15 to 35 km. The stratospheric ozone is not harmful, but its presence on land is harmful. It contains chlorofluorocarbons, halons, carbon tetrachloride, methyl chloroform, and nitrogen oxides. The ozone layer is mainly found in the lower portion of the stratosphere. It is approximately 15 to 35 km above Earth, although its thickness varies seasonally and geographically. The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. The ozone layer absorbs 97 to 99% of the sun’s medium-frequency ultraviolet light, from about 200 nm to 315 nm wavelength, which otherwise would potentially damage exposed lifeforms near the surface.
Production and destruction of atmospheric ozone
Stratospheric ozone
Ozone is an allotop of oxygen. Ozone molecules is made up of three oxygen atoms and is given the symbol O3. It is a strong oxidizing and chemically highly reactive gas and is present in the free atmosphere in varying quantities. 90% of the total ozone in the atmosphere is located in the stratosphere and only about 10% is in the layer between 12 km and Earth’s surface. The amount of ozone in the atmosphere is measured in terms of its thickness or height of a column of ozone if all the ozone in that atmospheric column were brought to Earth’s surface under the conditions of standard temperature and pressure. The unit of measurement of ozone in the atmospheric column is Dobson unit, dU. 1 dU is equal to 10 to 3 cm. Concentration of ozone begins to increase from about 12 to 14 km and the maximum is achieved at a height of about 25 km in the stratosphere. Even in the stratosphere, total amount of ozone is quite small as only 10 ozone molecules per million molecules of air are present. Total column ozone varies between more than 300 dU to 260 dU at poles and equator respectively. The total thickness of ozone layer is very, very small and is equivalent to about 3 mm of the column of atmosphere at standard atmospheric temperature and pressure at the Earth’s surface. Ozone is produced at the stratosphere by ionization or photodissociation of oxygen in the presence of UV radiation from the sun. In spite of splitting of oxygen molecule, oxygen remains abundant in the atmosphere by the reconvention of ozone into oxygen.
Tropospheric ozone
Small quantity of ozone occurs also in the troposphere and near the Earth’s surface. Pre-industrial era estimate of global average tropospheric ozone is 25 dbs units. At present, this has increased to a global average of 34 dbs units. Ozone is injected down in the troposphere from the stratosphere in the region after proposed break in the middle latitudes. Such exchanges take place in the regions of deep convention in the tropics, which allow such stratospheric-tropospheric exchanges through the penetrative convect of cloud tops. Small quantitative quantities of O3 can also be locally produced by flushes of atmospheric electricity in thunderstorms or through any electric spark.
Ozone hole
Depleted ozone in the stratosphere over Antarctic happens at the beginning of Southern hemisphere spring from August to October. It is the training of ozone layer which increases the penetration of ultraviolet rays on the earth surface.
Conventions regarding the ozone hole depletion
Vienna Convention of 1985 entered into force in 1982. It is a multilateral environmental agreement. It is not legally binding. It is one of the most successful treaties. It is ratified by 198 members. It acts as the framework of international efforts to protect the ozone layer. It is laid out in accompanying Montreal Protocol.
The Montreal Protocol is an international treaty. It is the updated version of the Vienna Convention. It is the first treaty in history to achieve universal ratification by every member state of UN. It aims to protect the ozone layer by phasing out CFCs, HCFCs, HBFCs, CCI4, methyl bromine, bromofluoromethane, methyl chloroform, haline, etc.
The Kigali Agreement of 2016 amends the Montreal Protocol to phase out hydrofluorocarbons by late 2040s and to prevent the potential 0.5 degree Celsius rise in global temperature.
The Indian laboratories in Antarctica are Dakshin Gangotri established in 1984. It is the first Indian base. It is currently used as a supply base and transit camp. The second is Maitri, and the third is Bharati. All of them are active.
