This presentation explains the Earth's atmosphere and its composition and variation of temperature and pressure in different layers of the atmosphere. It contains atmospheric circulation in troposphere and stratosphere. It explains the process of ozone formation and how its stability affects by the other chemical components which lead to the ozone depletion and ozone hole. It also contains the cosmic ray theory of ozone hole.

1. THE OZONE LAYER:
FORMATION AND DEPLETION
Presented by:
Kamran Ansari
Center for Basic Sciences,
PtRSU, Raipur
Date: 06 - 03 - 2019

2. Contents
• Earth’s atmosphere and its composition.
• Variation of different atmospheric parameters (e.g. Temperature,
Pressure and Density).
• Formation of stratospheric ozone.
• Ozone hole and ozone depletion.
• Cause of ozone depletion.

3. Earth’s atmosphere and its composition
• Atmosphere is a set of layers of different gases that surrounds a
planet (e.g. Earth) and retained by planet’s gravity.
• Earth is a only planet in the solar system with an atmosphere having
all the necessary component that can sustain life.
- Protecting from high energetic and harmful radiation from Sun.
- Create different weather system.
- Appropriate pressure for forming important gases.
- Maintains the surface temperature.

4. Fig. 1 : Different gas composition in Earth’s atmosphere.
Courtesy : Wikipedia

5. Vertical thermal structure of Earth’s Atmosphere
• Troposphere – Temperature decreases with
altitude due to less radiation comes from
Earth’s surface with altitude.
• Stratosphere – Temperature increase with
altitude due to ozone absorb UV radiation
during photolysis.
• Mesosphere – Temperature decreases with
altitude due to abundance of radiation
absorbing molecules.
• Thermosphere – Temperature increases with
altitude due to ionized O2 and N2 molecules
present.
Fig. 2 : Vertical structure of temperature in different layer.
Courtesy : C. Donald Ahrens-Essentials of Meteorology - An Invitation to the Atmosphere

6. • In the case of Hydrostatic equilibrium in atmosphere, the hydrostatic
condition is,
𝜕𝑃
𝜕𝑧
= −𝜌𝑔
For isothermal condition,
𝑃 𝑧 = 𝑃0 𝑒−𝑧/𝐻
𝑃0 = standard atmospheric pressure at sea level = 1.01 x 105 Pa
H = scale height =
𝑅𝑇
𝑀𝑔
𝜌 𝑧 = 𝜌𝑠 𝑒−𝑧/𝐻
𝜌𝑠 = density of air at sea level is approx. 1.225 kg/m3 at temperature 15◦C.
Vertical variation in Atmospheric pressure

7. Fig. 3 : (a) Variation of air density and air molecules with altitude, and (b) Variation of
atmospheric pressure.
Courtesy : C. Donald Ahrens-Essentials of Meteorology - An Invitation to the Atmosphere
(b)(a)

8. Depends on the temperature, extent of water vapor, wind pattern in
that latitude makes several pressure belts are:
1. Equatorial Low Pressure Belt,
2. Sub - Tropical High Pressure Belt,
3. Sub - Polar Low Pressure Belt, and
4. Polar High Pressure Belt.
Horizontal variation in Atmospheric pressure

9. Fig. 4 : Atmospheric circulation on Earth’s troposphere.
Courtesy : Wikipedia

10. • Atmospheric circulation in stratosphere :
- Temperature inversion in stratosphere makes warmer layers above
and cooler layers below, makes the stratosphere dynamically stable in
vertical.
- No regular convection and associated turbulence.
- The horizontal mixing of gaseous components proceeds much more
rapidly than does vertical mixing.

11. Fig. 5 : Atmospheric circulation on Earth’s stratosphere (Brewer-Dobson circulation).
Courtesy : Wikipedia

12. Formation of Stratospheric Ozone (O3)
Fig. 5 : The vertical distribution of atmospheric ozone.
Courtesy : Wikipedia
Ozone (O3) is most abundant gas component in stratosphere absorb most
of the Sun’s ultraviolet radiation, this region is also ozone layer. The
photochemical mechanisms for the formation of ozone were discovered
by the British physicist Sydney Chapman in 1930.

13. Fig. 6 : The process of ozone photochemical production.
Courtesy : www.theozonehole.com/ozonecreation.htm

14. Fig. 7 : Global distribution of ozone by NASA AURA Satellite (OMI) on 27th Feb 2019.
Courtesy : NASA - Ozone Monitoring Instrument (OMI)

15. • Normal ozone concentration is about 300 to 350 DU.
• The term “Ozone hole” is applied over region when stratospheric ozone
depletion is so severe that levels fall below 200 DU.
• Ozone loss now occurs every late winter and spring time above Antarctica
(South pole), and to a lesser extent the Arctic (North pole).
• Special meteorological conditions and very low air temperatures accelerate
and enhance the destruction of ozone loss by man-made ozone depleting
chemicals (ODCs).
Ozone Depletion and Ozone Hole

16. 1. NOx Catalytic Cycles
In 1970, Dr. Paul Crutzen showed that the nitrogen
oxides NO and NO2 react catalytically (without
themselves being consumed) with ozone, thus
accelerating the rate of reduction of the ozone
content.
NO + O3 NO2 + O2
NO2 + O NO + O2
Net Reaction: O3 + O 2O2
CAUSES OF OZONE DEPLETION
Fig. 8 : Paul Crutzen.
Courtesy : Photo from the Nobel Foundation archive.

17. 2. Chlorine Catalytic Reactions
Dr. M. Molina and Dr. S. Rowland in 1974
suggested that a man-made group of compounds
known as the chlorofluorocarbons (CFCs) were
likely to be the main source of ozone depletion.
CFCs (also known as Freon) are non-toxic, non-
flammable and non-carcinogenic. CFCs are very
stable gas and can remain 20 to 200 years.
CFCs are broken down by ultraviolet (UV) rays from
the Sun, releasing free chlorine which becomes
actively involved in the process of destruction of
ozone.
Fig. 9 : Mario J. Molina.
Courtesy : Photo from the Nobel Foundation archive.
Fig. 10 : F. Sherwood
Rowland .

18. Cl + O3 ClO + O2
ClO + O Cl + O2
Net Reaction: O3 + O 2O2
• Leaving the chlorine atom free to repeat the process up to 1,00,000
times, resulting in a reduced level of ozone.
• Highly reactive trace-gas molecules known as radicals dominate
stratospheric ozone destruction, and a single radical in the
stratosphere can destroy up to 10,000 ozone molecules before being
deactivated and removed from the stratosphere

19. Fig. 10 : Destruction of ozone by Chlorofluorocarbons (CFCs).
Courtesy : Sivasakthivel.T and K.K.Siva Kumar Reddy, Ozone Layer Depletion and Its Effects:
A Review, 2011, International Journal of Environmental Science and Development.

20. Why has an “ozone hole” appeared over Antarctica when ozone-
depleting substances are present throughout the stratosphere?
Fig. 11 : Minimum Air Temperature in the Polar Stratosphere.
Courtesy : www.esrl.noaa.gov/csd/assessments/ozone/2010/twentyquestions/Q10.pdf
Polar stratospheric clouds (PSCs) are important components of the ozone depletion process in the
polar regions of the Antarctic and the Arctic. PSCs provide the surfaces upon which chemical reactions
involved in ozone destruction take place.

21. Fig. 11 : A comparison of chlorine monoxide (left) and ozone concentration (right)
derived by MLS at approximately 18 km altitude on August 30, 1996.
Courtesy : NASA Earth Observatory.

22. OzoneDepletion
(DU/km)
Years
Fig. 12 : A comparison of Ozone depletion (up) and monthly average daily Sunspot number
(down) during 1950 -2000.
Courtesy :Hathaway, D.H. Living Rev.
Sol. Phys. (2015) 12: 4.
https://doi.org/10.1007/lrsp-2015-4
Courtesy : Sivasakthivel.T and K.K.Siva
Kumar Reddy, Ozone Layer Depletion and
Its Effects: A Review, 2011, International
Journal of Environmental Science and
Development.
Cosmic ray theory for ozone hole

23. They suggested that dissociation of chlorofluorocarbons by capture of electrons
produced by cosmic rays and localized in polar stratospheric cloud ice may play a
significant role in causing the ozone hole.

24. Fig. 13 : (a) Cosmic-ray ionization-rate variation as a function
of altitude, (b) Dependence of ozone loss on altitude.
Fig. 14 : (a) Cosmic-ray intensity as a function of latitude, (b)
Monthly average ozone concentrations in pre ozone hole and
ozone hole period.Courtesy :WMO Global Ozone Research and Monitoring Project–Report No. 44, p. 27
Courtesy :NASA TOMS satellite database

26. • Earth’s atmosphere and its composition,
• Variation of different atmospheric parameters,
• Formation of stratospheric ozone,
• Ozone Depletion and Ozone Hole,
• Cause of ozone Depletion.
Summary

27. References
• K. Mohanakumar - Stratosphere troposphere interactions: An introduction
(2008, Springer).
• C. Donald Ahrens-Essentials of Meteorology: An Invitation to the
Atmosphere-Brooks Cole (2011).
• Sivasakthivel. T and K. K. Siva Kumar Reddy, Ozone Layer Depletion and Its
Effects: A Review, 2011, International Journal of Environmental Science
and Development.
• Q.-B. Lu and L. Sanche Phys. Rev. Lett. 87.
https://doi.org/10.1103/PhysRevLett.87.078501
• Hathaway, D.H. Living Rev. Sol. Phys. (2015) 12: 4.
https://doi.org/10.1007/lrsp-2015-4

28. Thank You