Ozone and its Depletion - Environmental Science

A presentation covering introduction to the ozone layer, followed by a deep dive into the ozone depletion - sources, causes, effects, and solutions.

1. Ozone Depletion

2. Introduction1.
Ozone Layer2.
Ozone-Oxygen Cycle3.
Ozone Depletion4.
Sources of depleting substances 5.
Ozone depletion process6.
Ozone Hole7.
Effects of ozone depletion8.
Solution9.
Table of Contents

3. The ozone layer is a region of Earth’s
stratosphere that absorbs most of the Sun’s
UV radiation. Protects living organisms
from its harmful effects.
The ozone layer is found in the lower
portion of the stratosphere. It is about 20-30
km above earth’s surface.
It’s thickness varies seasonally and
geographically.
Introduction

4. Ozone Layer

5. Layers of the Atmosphere
Troposphere
Thermosphere
MesosphereStratosphere
Exosphere
Lowest layer of atmosphere
10km above surface
Rain,wind snow and other
weather conditions occur
Second layer of atmosphere
10-50km above Earth’s surface
Ozone layer present here
Fourth layer of the atomosphere
Extends between 85-600 km above Earth’s
surface
Hottest layer due to high UV radiation
Third layer of atmosphere
50-85 km above Earth’s surface
Temperature decreases rapdily
with altitude
Outermost layer of the atomosphere
Extends between 600-10000 km above
Earth’s surface
Very thin, allowing escape of particles into
space

7. The Ozone Layer
Region of Stratosphere
High concentration of Ozone
Acts as a shield
Absorbs UV radiation - UVB(280-315nm) and
UVC(<280nm)
UV rays can cause:
Human: Skin Cancer, Cataracts and immune
system supression
Environment: Damage to plant and environmental
life, affecting the ecosystem

9. The ozone–oxygen cycle is the process by which ozone is continually regenerated
in Earth's stratosphere, converting ultraviolet radiation (UV) into heat.
In 1930 Sydney Chapman resolved the chemistry involved. The process is
commonly called the Chapman cycle by atmospheric scientists
Most of the ozone production occurs in the tropical upper stratosphere and
mesosphere.
The Chapman cycle describes the main reactions that naturally determine, to first
approximation, the concentration of ozone in the stratosphere. It includes four
processes - and a fifth, less important one - all involving oxygen atoms and
molecules, and UV radiation
Ozone–oxygen cycle

10. Oxygen Photodissociation: UV light splits O2
into two oxygen atoms.
O2 + ℎν(<242 nm) → 2 O
Ozone Creation: Each oxygen atom may then
combine with an oxygen molecule to form an
ozone molecule with a third molecule (A)
conserving energy and momentum.
O + O2 + A → O3 + A
Ozone–Oxygen Cycle: Ozone absorbs UV light,
splitting into O2 and a free oxygen atom, which
can reform ozone, converting UV light into heat.
O3 + ℎν(240–310 nm) → O2 + O
Ozone Removal: Oxygen atoms can recombine
with ozone to form O2, or two oxygen atoms can
form O2 with a third molecule (A).
O3 + O → 2 O2 2O + A → O2 + A

11. Ozone layer depletion refers to the reduction
of ozone in the Earth's stratosphere, mainly
due to chlorine and bromine from man-made
compounds.
Chlorine and Nitrogen Oxides from ozone-
depleting substances like CFCs and halons
react with and destroy ozone molecules.
One chlorine atom can destroy up to 100,000
ozone molecules, causing rapid depletion of
the ozone layer.
Ozone depletion

12. Ozone Depleting Substances-Chlorine(Cl)
Role in Ozone Depletion:1.
Chlorine, primarily from chlorofluorocarbons (CFCs) is
released into the stratosphere, where it catalyzes the
destruction of ozone molecules.
Chemical Reaction:2.
Chlorine atoms react with ozone (O3) molecules, resulting
in the formation of oxygen (O2) and chlorine monoxide
(ClO).
Source of Chlorine:3.
CFCs, halons, and other man-made chemicals used in
refrigeration, air conditioning, foam blowing agents, and
solvents.
Environmental Impact:4.
increased levels of harmful ultraviolet (UV) radiation
reaching the Earth's surface, resulting in higher risks of
skin cancer, cataracts, and negative effects on ecosystems
and wildlife.

13. Ozone depleting substances-NOx
1.Sources of NOx in the Stratosphere:
Natural sources: lightning, biological ,volcanic erruptions.
Anthropogenic sources: Fossil Fuel Combustion, Aircraft Emissions, Use of Fertilizers
2.Mechanism of Ozone Depletion by NOx:
a) Formation of NOx in the Stratosphere:
NOx can be transported to the stratosphere from the troposphere, or it can be produced in
situ through natural processes like solar radiation and lightning.
b) Reaction with Ozone (O3):
NO reacts with Ozone: NO+O3->NO2+O2
NO2 can then react with atomic oxygen (O):NO2+O->NO+O2
c) Catalytic Cycle:
NO and NO2 participate in a catalytic cycle that destroys ozone without being consumed in
the process.
The overall reaction can be summarized as: O3+O->2O2

14. Ozone Depletion Process
UV radiation breaks off a chlorine atom from a CFC molecule.
The chlorine atom attacks an ozone molecule, breaking it apart and destroying the
ozone.
The result is an ordinary oxygen molecule and a chlorine monoxide molecule .
The chlorine monoxide molecule is attacked by a free oxygen atom releasing the
chlorine atom and forming an ordinary oxygen molecule .
The chlorine atom is now free to attack and destroy another ozone molecule. One
chlorine atom can repeat this destructive cycle thousands of times.

16. Ozone hole
Ozone depletion consists of two related events observed since the late 1970s: a steady
lowering of about four percent in the total amount of ozone in Earth's atmosphere,
and a much larger springtime decrease in stratospheric ozone (the ozone layer)
around Earth's polar regions. The latter phenomenon is called ozone hole.

18. Increased UV Radiation: Effect of Ozone Depletion on Increased UV Radiation,
Human Health, Environmental Impact, Climate, and Materials
Human Health: Higher UV radiation due to ozone depletion increases the risk of
skin cancers.
Environmental Impact: Ozone depletion leads to increased UV radiation reaching
the Earth's surface.
Climate, and Materials: Higher UV radiation levels due to ozone depletion can
accelerate the degradation of materials exposed to sunlight
Effect Of Ozone Depletion

19. What Can We Do to
Make it Better?
There are several ways we can stop this
depletion too.

20. Restoring decades of damage to the ozone layer
will take time.
But our lives, industry, transport, electricity
sources, and food systems have been built on
carbon-emitting fuels. Many of these
infrastructural systems have a lifetime that lasts
decades.
The good news is that the cost of low-carbon
energy sources is plummeting.

21. Using public transport or carpooling as an
alternative
Always buy energy efficient appliances to
reduce the release of CFC’s.
Plant more trees. Try maintaining a garden
around your house in order to reduce the
amount of ultraviolet radiations, since trees
can absorb most of it.
Stop the excessive usage of insecticides and
pesticides.
Some simple ways

22. Thank You!