Environment · X-Factor Notes
Ozone Layer (Chapter 5) revision notes for UPPCS Prelims.
High-Yield Revision| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Location (Layer) | The ozone layer is primarily found in the Stratosphere. The layer is mainly found in the lower portion of the stratosphere, approximately 15 to 30 kilometres above the Earth. | UP PCS Pre (Spl) 2008, UP UDA/LDA Spl Mains 2010, UP PCS Mains 2012, UP P.C.S. Pre 2018, UPPSC Prelims 2023 |
| Concentration/Distribution | Maximum concentration of ozone is found in the Stratosphere. 90% of the ozone layer is found in the stratosphere, and 10% in the troposphere. | UP P.C.S. Pre 2018 |
| Natural Regulation | The level of ozone in the stratosphere is naturally regulated by Nitrogen Dioxide (NO2). | UP PCS Mains 2016 |
| Measurement | The measuring unit of the ozone layer is the "Dobson Unit" (DU). One DU is equal to 0.01 mm thickness of pure Ozone at O3 temperature and 1 atm pressure. | UP PCS Mains 2016 |
| Ozone Nature | Ozone (O3) consists of three atoms of oxygen. Ozone is a pollutant on the surface of the earth (lower atmosphere) and is harmful to living organisms, causing direct and immediate harm to the lungs and entire respiratory system. |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Protective Function | Ozone performs an essential function by shielding the Earth's surface from ultraviolet (UV) radiation. It absorbs UV radiation. It blocks high wavelength ultraviolet light from the Sun by 93% to 99%. | UP PCS Pre 2013, UP PCS Pre 2014 |
| Formation | Stratospheric ozone is formed naturally by chemical reactions involving solar ultraviolet radiation and oxygen molecules | UP P.C.S. Pre 2018 |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Primary Depleter | Chlorofluorocarbons (CFCs) are the main gas/pollutant causing maximum damage and responsible for the decrement/depletion of the ozone layer. | UP PCS Pre 2016, UP RO/ARO Pre 2014 |
| ODS Examples | Other ozone-depleting substances include Halon - 1211, 1301, Nitrous oxide, and Carbon tetrachloride(CCl4). | UP PCS Pre 2012, UP PCS Pre 2002 |
| CFC Usage |
| Concept | What to remember | Asked in UPPCS |
|---|---|---|
| Major Treaty | The Montreal Protocol is the international treaty associated with the issue of control and phasing out the use of ozone-depleting substances. | |
| Timeline | The Montreal Protocol was signed on 16 September 1987 and came into force on 1 January 1989. | |
| World Ozone Day |
| Harmful Impact |
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| Harmful ultraviolet radiation coming from the Sun can cause skin cancer in human beings. Exposure for a long time can cause genetic mutation. |
| UP PCS Pre 2014 |
| CFCs are highly stable (sustaining for 80 to 100 years) and are used as coolants in refrigerators and air conditioners, in the production of plastic foams, for cleaning certain electronic components, and as pressurizing agents in aerosol cans. |
| Ozone Hole | The ozone hole is a region of exceptionally depleted ozone in the stratosphere over Antarctica. The effect of ozone layer depletion is maximum over the poles. |
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| Discovery | The British team first discovered the ozone hole over Antarctica in 1985. | UP PCS Mains 2013 |
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| Mechanism | The presence of Polar stratospheric clouds helps chlorine compounds convert into chlorine atoms, which photo-chemically destroy the ozone layer. | UP PCS Mains 2016 |
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| September 16 is observed annually as the International Day for the Preservation of the Ozone Layer (since 1994). |
| UP PCS Pre 1996, UP PCS Pre 2014, UP PCS Pre 2015, UPPSC Prelims 2022 |
| Ozone Day Theme | The theme for World Ozone Day 2025 was “From Science to Global Action” Purpose: Raise awareness about the ozone layer, its depletion, and climate change impact |
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