Ozone depletion over the Tropics

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.

• 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.