Context

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

About

• 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.

Ozone: Ozone is a special form of oxygen, made up of three oxygen atoms rather than the usual two oxygen atoms. It usually forms when some type of radiation or electrical discharge separates the two atoms in an oxygen molecule (O2), which can then individually recombine with other oxygen molecules to form ozone (O3).

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.