18th July 2022 (7 Topics)
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Ozone depletion over the Tropics
Context
Recently a study done by AIP Advances claimed that a new ozone hole has been detected over the tropics, at latitudes of 30 degrees south to 30 degrees north.
Background
- Ozone depletion consists of two related events observed since the late 1970s;
- A steady lowering of about four per cent in the total amount of ozone in Earth's atmosphere, and
- A much larger springtime decrease in stratospheric ozone (the ozone layer) around Earth's Polar Regions.
- The latter phenomenon is referred to as the ozone hole.
- The main causes of ozone depletion and the ozone hole are manufactured chemicals, especially manufactured halocarbon refrigerants, solvents, propellants, and foam-blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons), referred to as ozone-depleting substances(ODS).
- Hence, several measures have been taken worldwide for conserving ozone depletion.
- In 2019, NASA reported that the ozone hole was the smallest ever since it was first discovered in 1982.
Key highlights of the study
- According to the study the ozone hole is located at altitudes of 10-25 km over the tropics.
- The tropical ozone hole is about seven times larger than
- The hole has become significant since the 1980s, and makes up 50 per cent of Earth’s surface.
- It appears across all seasons, unlike that of Antarctica, which is visible only in the
- It is likely to cause skin cancer, cataracts and other negative effects on the health and ecosystems in tropical regions.
- Cause: Chlorofluorocarbon’s (CFC) role in depleting the ozone layer over Tropics also.
- Evidence: The tropical stratosphere recorded a low temperature of 190-200 Kelvin (K), which is lower than the normal tropical stratospheric levels.
- Procedure Adopted: Comparative study of the relative ozone changes in per cent in the 2000s with those in
- These observed results were then compared to datasets from combined ground-based and satellite measurements used by other researchers.
Different definitions to Ozone Hole
- Normally, a region of marked thinning of the ozone layer in high latitudes, chiefly in winter, attributed to the chemical action of CFCs and other atmospheric pollutants.
- According to NASA, an ozone hole is an area where ozone levels drop below the historical threshold of 220 Dobson Units(DU is the measure of ozone concentrations).
- Mechanism of Ozone depletion:
- The pollutants are transported into the stratosphere by turbulent mixing after being emitted from the surface, mixing much faster than the molecules can settle.
- Once in the stratosphere, they release atoms from the halogen group through photo dissociation, which catalyse the breakdown of ozone (O3) into oxygen (O2).
Is this study accepted worldwide?
- Other experts not involved in the study have raised doubts about the study’s claims.
- Issues aroused:
- There were very few observations in the 1960s, from which the study’s data has been compared for tropical ozone depletion.
- There are other better ozone datasets which are used widely in the community to determine ozone trends from the 1960s. They do not show this large drop in ozone.
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