World's Ozone Hole

    By 1985 Jonathan Shanklin, a materologist with the British Antarctic Survey, Joe Farman and Brian Gardiner published that CFCs, man made compound used in aerosols and cooling devices , is responsible for the thinning of the ozone layer over the Antarctica's Halley Bay research station.Ozone gas is found in the 10-50 km above the Earth surface (stratosphere) and acting as UV radiation, known as UV-B, absorbing layer, so it is termed as Earth's sunscreen.

 Photo courteasy :- NASA

   In 1974 Mario Molina and F.Sherry Rowland, the 1995 Noble literature in Chemistry were  reported that CFCs could destroy ozone layer of stratosphere and in 1985 it was confirmed by the British Antarctic Survey.Susan Soloman, a researcher with the US government National Ocenic and Atmospheric Administration, in 1985  explained the main cause of the ozone hole and it was over 20 million sq kilometres.

    Ozone depletion might results into rise  in skin cancer, cataract, plant growth inhibition, reproductive problem in the aquatic flora and fauna, ecosystem damage,etc.

   On September 16, 1987, the Montreal Protocol on Substances that deplete the ozone layer was adopted to protect the ozone layer in the face of a triple planetary crisis-- climate, nature and pollution. It came into effect in 1989 and by 2008 it was ratified by every country in the world. As a result 99% ozone-depleting substances have been phased out and it is expected that ozone hole will close by about 2065 , and other regions will return to pre-1980s values even earlier. Before that, in 1985 the Vienna Convention for the protection of ozone layer was adopted.

   In 2018 , the Environmental Investigation Agency traced that  CFC-11 or ozone depleting trichlorofluoromethane, is emitted from the Chinese insulation foam industries though CFC-11 was banned since 2010. In 2019 the Kigali Amendment came into force to the use of more energy-efficient cooling system.

     Nitrous oxide, a greenhouse gas, emmited from chemical fertilizers and  natural volcanic eruptions result in ozone depletion. The 1991 Mount Pinatubo eruption and the 2022 Hunga Tonga- Hunga Ha'apai volcanic eruption have  released sulphur-dioxide which amplified the ozone layer depletion.

Dobson Spectrophotometer: 

       1 Dobson Units = a layer of pure ozone of 0.01 mm thick at a standard temperature and pressure. It is named after Gordon Dobson of University of Oxford, who in 1920s  built the first instrument to measure total ozone layer from the ground.

    Globally , the total ozone column average is 300 Dobson units. On October 3,2022, it was of 101 Dobson units over the South Pole and during that time ozone was completely absent at the altitude between 14- 21 kilometres.

Ozone formation:  The Stratospheric oxygen absorbs UV-C of the sunlight and itself splits into oxygen atoms . These atoms react with the oxygen molecules to increase ozone layer in the stratosphere.

World Ozone Day :

         In 1994 , the UN General Assembly proclaimed 16 th September as the world Ozone day to commemorating the date of signing the Montreal Protocol ,1987 .  

      The  Montreal Protocol provisions were strengthened through five amendments to the Protocol adopted in :-

London(1990),

Copenhagen (1992),

Vienna(1995),

Montreal (1997) and

Beijing (1999).

Role of India: India acceded to the Montreal Protocol on 17th September,1992:

(i) The production of CFC-11, 12 and 113 has been phased out from 1st August,2008 and there consumption has been phased out from 1st January,2010.

(ii) From 1st. January,2010 production and consumption of carbon tetrachloride has been phased out.

(iii) For Halon-1211 and Halon- 1301 , the production and consumption has been phased out from 1st January,2002.

(iv) The consumption of methyl chloroform has been phased out from January 2001.

Since 2000, the ozone layer is increased by 1-3% in every ten years.

Harmful effects of ozone:  At 0.02 pm concentration near earth's surface , ozone may cause damage to tobacco, tomato, bean and grapes plants. Leaves are damaged by high concentration of ozone.

 MCQ 

Q1. Depletion of Stratospheric ozone results into:

(A) Increase in UV radiation 

(B) Increase in infra- red radiation 

(C) Increase in skin cancer 

(D) Significant impact on terrestrial flora and fauna 

(E) Decrease in cataract eye

Choose the correct answer:

1. A,B,C & D only

2. A,C & D only (ans)✓

3. B, C, D and E only

4. A, B & C only.

Q2 . Which of the following is not responsible for the destruction of ozone layer:

(A) CFC

(B) Halons

(C).Dioxins (ans)✓

(D).HCFC

Q3.Discovery of ozone hole was first made over :

(A)Arctic 

(B) Equator

(C) Antarctic (ans)✓

(D) Tropics

Q4. Which one is destructive to ozone layer:

(A) CO2

(B) CFC (ans)✓

(C) N2O

(D) CH4

Q5. Ozone hole is observed at

(A)Equator

(B) Tropic of Cancer 

(C)Tropic of Capricorn 

(D) Poles (ans)✓

Q6. Maximum ozone depletion is at

(A)The North Pole

(B) The South Pole (ans)✓

(C) The Equator 

(D) The Tropics 

Q7. Ozone layer is found in: 

(A) Stratosphere (ans)✓

(B) Mesosphere 

(C) Exosphere

(D)Troposphere

Q8. Ozone depletion results into 

(A)Heart attack 

(B) Skin Cancer (ans)✓

(C)Brain stroke 

(D)TB

Q9.Which one causes ozone depletion 

(A) CFCs (ans)✓

(B) PVC

(C)Biopolymer

(D)Methanol

Q10. Convention on Ozone depletion is the

(A) Montreal Protocol (ans)✓

(B) Basel Convention 

(C)Kyoto Protocol 

(D)None of the above

Q11. World Ozone Day is celebrated on

(A) 16:th September (ans)

(B)

(C)

(D)

Q12. Measuring unit of Ozone is

(A) DU ✓

Author: Prasenjit Sinha, Department of Botany and Co-ordinator of AEC on Environmental Studies, Ramkrishna Mahavidyalaya, Kailashahar, Tripura.