Largest Arctic Ozone hole closes itself up

Scientists have revealed that the largest hole ever observed in the ozone layer above the Arctic last month has healed itself.

• The ozone layer protects Earth from Sun’s harmful ultraviolet rays. It is found in Earth’s stratosphere, a layer of the atmosphere around 10–50 kilometres above sea level.
• Stratospheric ozone is constantly produced by the action of the sun's ultraviolet radiation on oxygen molecules (known as photochemical reactions).
• Ozone is found in two different parts of our atmosphere.
  • Ground level or “bad” ozone: It is a human health irritant and component of smog. It is found in the lower atmosphere (troposphere) and has nothing to do with the "ozone hole."
  • High level or “good” ozone: It occurs in the stratosphere and accounts for the vast majority of atmospheric ozone.
• Although ozone is created primarily at tropical latitudes, large-scale air circulation patterns in the lower stratosphere move ozone toward the poles, where its concentration builds up.

How ozone works?

• The sun emits electromagnetic radiation at different wavelengths, meaning energy at different intensities.
• The atmosphere acts like a multi-layer shield that protects Earth from dangerous solar radiation.
• The stratospheric ozone layer absorbs ultraviolet (UV) radiation, preventing dangerous UV rays from hitting Earth's surface and harming living organisms.
• Ozone is good at trapping a type of radiation called ultraviolet radiation, or UV light, which can penetrate organisms’ protective layers, like skin, damaging DNA molecules in plants and animals.
• There are two major types of UV light: UVB and UVA.
  • UVBis the cause of skin conditions like sunburns, and cancers like basal cell carcinoma and squamous cell carcinoma.
  • UVA light is even more harmful than UVB, penetrating more deeply and causing a deadly skin cancer, melanoma, and premature aging.

Formation of hole in the ozone layer:

• The hole formed earlier this year and reached its maximum size in March some 11 miles above the surface of the Earth.  
• It was the largest ozone hole ever documented over the Arctic, beating the previous record holder, which was observed during the 2011 winter.
• Scientists had attributed the forming of the hole in the ozone layer above the North Pole to unusually low temperatures in the atmosphere above the region.
• The researchers from the German Aerospace Center (DLR) discovered the hole using data from the Copernicus Sentinel–5P satellite.

Reason behind Ozone depletion:

• Ozone depletion occurs when chlorofluorocarbons (CFCs) and halons—gases formerly found in aerosol spray cans and refrigerants—are released into the atmosphere (see details below).
• CFCs and halons cause chemical reactions that break down ozone molecules, reducing ozone's ultraviolet radiation-absorbing capacity.

Reasons behind recovery:

• According to the scientists the recovery of the hole is not due to the reduced pollution levels due to COVID-19 lock down. The closing was because of a phenomenon called the polar vortex.
• High-altitude currents called polar vortex are responsible for bringing cold air to north pole and the subsequent healing of the ozone layer.