From UPSC perspective, the following things are important :
Prelims level : Ozone Layer, Ozone Hole
Mains level : Not Much
The ozone ‘hole’, once considered to be the gravest danger to planetary life, is now expected to be completely repaired by 2066, a scientific assessment has suggested.
What is Ozone and Ozone Layer?
- An ozone molecule consists of three oxygen atoms instead of the usual two (the oxygen we breathe, O2, makes up 21% of the atmosphere).
- It only exists in the atmosphere in trace quantities (less than 0.001%), but its effects are very important.
- Ozone molecules are created by the interaction of ultra-violet (UV) radiation from the Sun with O2 molecules.
- Because UV radiation is more intense at higher altitudes where the air is thinner, it is in the stratosphere where most of the ozone is produced, giving rise to what is called the ‘ozone layer’.
- The ozone layer, containing over 90% of all atmospheric ozone, extends between about 10 and 40km altitude, peaking at about 25km in Stratosphere.
Why need Ozone Layer?
- The ozone layer is very important for life on Earth because it has the property of absorbing the most damaging form of UV radiation, UV-B radiation which has a wavelength of between 280 and 315 nanometres.
- As UV radiation is absorbed by ozone in the stratosphere, it heats up the surrounding air to produce the stratospheric temperature inversion.
What is Ozone Hole?
- Each year for the past few decades during the Southern Hemisphere spring, chemical reactions involving chlorine and bromine cause ozone in the southern polar region to be destroyed rapidly and severely.
- The Dobson Unit (DU) is the unit of measure for total ozone.
- The chemicals involved ozone depletion are chlorofluorocarbons (CFCs for short), halons, and carbon tetrachloride.
- They are used for a wide range of applications, including refrigeration, air conditioning, foam packaging, and making aerosol spray cans.
- The ozone-depleted region is known as the “ozone hole”.
Tropical Ozone Hole
- According to the study, the ozone hole is located at altitudes of 10-25 km over the tropics.
- This hole is about seven times larger than Antarctica, the study suggested.
- It also appears across all seasons, unlike that of Antarctica, which is visible only in the spring.
- The hole has become significant since the 1980s. But it was not discovered until this study.
What caused an ozone hole in the tropics?
- Studies suggested another mechanism of ozone depletion: Cosmic rays.
- Chlorofluorocarbon’s (CFC) role in depleting the ozone layer is well-documented.
- The tropical stratosphere recorded a low temperature of 190-200 Kelvin (K).
- This can explain why the tropical ozone hole is constantly formed over the seasons.
Try this PYQ
Q.Consider the following statements:
Chlorofluorocarbons, known as ozone-depleting substances are used:
- In the production of plastic foams
- In the production of tubeless tyres
- In cleaning certain electronic components
- As pressurizing agents in aerosol cans
Which of the statements given above is/are correct?
(a) 1, 2 and 3 only
(b) 4 only
(c) 1, 3 and 4 only
(d) 1, 2, 3 and 4
Post your answers here:
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