Why in News?
According to World Meteorological Organization (WMO) Report,
On 20 September 2020, Antarctic ozone hole grew rapidly and peaked at around
24.8 million square kilometres and spreading over most of the Antarctic continent.
Key Points:
What is Ozone?
- Ozone is form of oxygen that combines three atoms into each
molecule. - The chemical symbol of ozone is O₃.
- It absorbs and filters the harmful ultraviolet B radiation
coming from the Sun. - This way the ozone layer protects all life on earth.
- The Dobson Unit (DU) is the unit of measurement for total ozone.
Ozone Layer:
Ozone Layer is found in the Stratosphere. Which is “good”
because it protects life on Earth by absorbing some of the sun’s harmful Ultra
Violet (UV) rays.
Note: Ozone in the troposphere is “bad” because it dirties
the air and helps to form smog, which is not good to breathe.
What is Ozone Depletion?
A steady decline in the concentration of ozone in the
earth’s stratosphere is called ozone depletion.
Why is Ozone Depletion occur?
Due to the influx of several substances into the atmosphere
which react with ozone and destroy it. For Example – When chlorofluoro carbon (CFC) and halon
gases, formerly found in aerosol spray cans and refrigerants are released into
the atmosphere and they cause chemical reactions that break down ozone molecules
and reduce the concentration of them.
Ozone-depleting Substances:
- chlorofluorocarbons (CFCs)
- Halon gases
- Carbon Tetrachloride (CCl4)
- Methyl Chloroform (CH3CCl3)
- Hydrochlorofluorocarbons (HCFCs)
- Hydrobromofluorocarbons (HBFCs)
- Methyl Bromide (CH3Br)
- Bromochloromethane (CH2BrCl)
- Nitrogen Oxides.
The UV rays cause direct damage to the genetic material or
DNA of animal and plant cells. Exposure of mammals to UV light has been shown
to act on the immune system, thereby making the body more susceptible to
diseases.
Why ozone hole occurs over Antarctica?
The severe depletion of the Antarctic ozone layer known as
the “ozone hole” occurs because of the special atmospheric and chemical
conditions that exist there and nowhere else on the globe. The very low winter
temperatures in the Antarctic stratosphere cause polar stratospheric clouds
(PSCs) to form. Special reactions that occur on PSCs, combined with the relative
isolation of polar stratospheric air, allow chlorine and bromine reactions to
produce the ozone hole in Antarctic springtime. Satellite images of the earth
over last decades observed that the atmospheric ozone layer is getting thinner.
On 20 September, 2020, the ozone hole was recorded to its maximum size of 28.2
million sq.km over Antarctica. The size of the ozone hole is larger than the
size of continent of North America.
Harmful Effect of Ozone Depletion:
- Depletion of the ozone layer has consequences on human,
animal, plants and micro-organisms. - The ozone holes allow the ultraviolet radiation to enter and
cause of global warming, skin cancer, eye cataract and even blindness.
using products which are emitting pollutants such as aerosol sprays, blowing
agents for foams and packing materials, as solvents and as refrigerants.