3. The ozone hole is the region
over Antarctica with total
ozone 220 Dobson Units or
lower. (The avg total column
ozone in the atmosphere is
about 300 DU.)
What is the “ozone hole?” When did it first appear? How does it form?
4. What is Ozone depletion?
Ozone depletion describes two distinct but related phenomena observed since the
late 1970s: a steady decline of about 4% per decade in the total volume
of ozone in Earth's stratosphere (the ozone layer)
A catalytic destruction of ozone by atomic halogens.
5. What is Ozone?
•Ozone or o3 is a highly reactive form
of oxygen.
•Unlike o2, it has a strong scent & is
blue in color.
•It exists both within the troposphere
& stratospheric zones of the earth’s
atmosphere
• In the troposphere, ground level
ozone is a major air pollutant as
primary constituent of photochemical
smog.
•In the stratosphere it acts as an
essential protector of life on earth as it
absorbs harmful uv radiation before it
reaches the earth.
7. The ozone layer is responsible for absorbing harmful ultraviolet rays, and
preventing them from entering the Earth's atmosphere. However, various factors
have led to the depletion and damage of this protective layer.
Ozone is formed when oxygen molecules absorb ultraviolet photons, and
undergo a chemical reaction known as photo dissociation or photolysis. In this
process, a single molecule of oxygen breaks down into two oxygen atoms. The
free oxygen atom (O), then combines with an oxygen molecule (O2), and forms
a molecule of ozone (O3). The ozone molecules, in turn absorb ultraviolet rays
between 310 to 200 nm (nanometers) wavelength, and thereby prevent these
harmful radiations from entering the Earth's atmosphere. The process of
absorption of harmful radiation occurs when ozone molecules split up into a
molecule of oxygen, and an oxygen atom. The oxygen atom (O), again combines
with the oxygen molecule (O2) to regenerate an ozone (O3) molecule. Thus, the
total amount of ozone is maintained by this continuous process of destruction,
and regeneration.
8.
9. • Ultraviolet radiations (UVR), are high energy electromagnetic waves
emitted from the Sun. UV radiation includes UV-A, the least dangerous
form of UV radiation, UV-B, and UV-C, which is the most dangerous. UV-
C is unable to reach the Earth's surface due to stratospheric ozone's ability
to absorb it. The real threat comes from UV-B, which can enter the Earth's
atmosphere, and has adverse effects.
Ozone layer depletion first captured the attention of the whole world in the
latter half of 1970, and since then, a lot of research has been done to find its
possible effects and causes. Various studies have also been undertaken to
find out a possible solution. We’ll later on take a look at some of the causes
and effects of ozone layer depletion.
10. The most pronounced decrease in ozone has been in the lower stratosphere.
However, the ozone hole is most usually measured not in terms of ozone
concentrations at these levels (which are typically of a few parts per million)
but by reduction in the total column ozone, above a point on the Earth's
surface, which is normally expressed in Dobson units, abbreviated as "DU".
Marked decreases in column ozone in the Antarctic spring and early
summer compared to the early 1970s and before have been observed using
instruments such as the Total Ozone Mapping Spectrometer (TOMS).[6]
11.
12. • CFCs and other contributory substances are referred
to as ozone-depleting substances (ODS). Since
the ozone layer prevents most harmful UVB
wavelengths (280–315 nm) of ultraviolet light (UV
light) from passing through the Earth's atmosphere,
observed and projected decreases in ozone have
generated worldwide concern leading to adoption of
the Montreal Protocol that bans the production of
CFCs, halons, and other ozone-depleting chemicals
such as carbon tetrachloride and trichloroethane. It
is suspected that a variety of biological consequences
such as increases in skin cancer,cataracts,damage to
plants, and reduction of plankton populations in the
ocean's photic zone may result from the increased
UV exposure due to ozone depletion.
13. Since the ozone layer absorbs UVB ultraviolet light from the sun, ozone layer
depletion is expected to increase surface UVB levels, which could lead to
damage, including increase in skin cancer. This was the reason for the Montreal
Protocol. Although decreases in stratospheric ozone are well-tied to CFCs and
there are good theoretical reasons to believe that decreases in ozone will lead to
increases in surface UVB, there is no direct observational evidence linking ozone
depletion to higher incidence of skin cancer and eye damage in human beings.
This is partly because UVA, which has also been implicated in some forms of
skin cancer, is not absorbed by ozone, and it is nearly impossible to control
statistics for lifestyle changes in the populace.
16. • Even minor problems of ozone depletion can have major effects. Every time even a
small amount of the ozone layer is lost, more ultraviolet light from the sun can reach
the Earth.
• Every time 1% of the ozone layer is depleted, 2% more UV-B is able to reach the
surface of the planet. UV-B increase is one of the most harmful consequences of
ozone depletion because it can cause skin cancer.
• The increased cancer levels caused by exposure to this ultraviolet light could be
enormous. The EPA estimates that 60 million Americans born by the year 2075 will
get skin cancer because of ozone depletion. About one million of these people will die.
• In addition to cancer, some research shows that a decreased ozone layer will increase
rates of malaria and other infectious diseases. According to the EPA, 17 million more
cases of cataracts can also be expected.
17.
18. • The environment will also be negatively affected by ozone
depletion. The life cycles of plants will change, disrupting the food
chain. Effects on animals will also be severe, and are very difficult to
foresee.
• Oceans will be hit hard as well. The most basic microscopic
organisms such as plankton may not be able to survive. If that
happened, it would mean that all of the other animals that are above
plankton in the food chain would also die out. Other ecosystems such
as forests and deserts will also be harmed.
• The planet's climate could also be affected by depletion of the ozone
layer. Wind patterns could change, resulting in climatic changes
throughout the world.
20. • Ozone is a triatomic form of oxygen (O3), found in the Earth's atmosphere. A combination of
low temperatures, elevated chlorine and bromine concentrations in the upper stratosphere are
responsible for the destruction of ozone. The production and emission of chlorofluorocarbons
(CFCs), is the leading cause of ozone layer depletion. CFC's accounts for almost 80% of the total
depletion of ozone.
Other ozone depletion substances (ODS), include hydrochlorofluorocarbons (HCFCs), and
volatile organic compounds (VOCs). These are often found in vehicle emissions, byproducts of
industrial processes, refrigerants, and aerosols. ODS are relatively stable in the lower atmosphere
of the Earth, but in the stratosphere, they are exposed to ultraviolet radiation and thus, they
break down to release a free chlorine atom.
• This free chlorine atom reacts with an ozone molecule (O3), and forms chlorine monoxide
(ClO), and a molecule of oxygen. Now, ClO reacts with an ozone molecule to form a chlorine
atom, and two molecules of oxygen. The free chlorine molecule again reacts with ozone to form
chlorine monoxide. The process continues, and this results in the depletion of the ozone layer.
21.
22. Possible Effects of Ozone Depletion
As ozone depletes in the stratosphere, it forms a 'hole' in the layer. This hole enables harmful ultraviolet rays to
enter the Earth's atmosphere. Ultraviolet rays of the Sun are associated with a number of health related, and
environmental issues. Let us take a look at how ozone depletion effects different life forms.
Impact on Humans
Skin cancer: Exposure to ultraviolet rays poses an increased risk of developing several types of skin cancers,
including malignant melanoma, basal and squamous cell carcinoma. Eye damage: Direct exposure to UV
radiations can result in photokeratitis (snow blindness), and cataracts.
Immune system damage: Effects of UV rays include impairment of the immune system. Increased exposure to
UV rays weakens the response of the immune system.
Accelerated aging of skin: Constant exposure to UV radiation can cause photo allergy, which results in the
outbreak of rash in fair-skinned people.
Other effects: Ozone chemicals can cause difficulty in breathing, chest pain, throat irritation, and hamper lung
functioning.
23.
24. Effects on Amphibians
Ozone depletion is listed as one of the causes for the declining numbers of amphibian species.
Ozone depletion affects many species of amphibians at every stage of their life cycle. Some of
the effects are mentioned below.
Hampers growth and development in larvae
Changes behavior and habits
Causes deformities in some species
Decreases immunity. Some species have become more vulnerable to diseases and death
Retinal damage and blindness in some species
Effects on Marine Ecosystems
In particular, plankton (phytoplankton and bacterioplankton) are threatened by increased UV
radiation. Marine phytoplankton play a fundamental role in both the food chain as well as the
oceanic carbon cycle. Plankton play an important role in converting atmospheric carbon dioxide
into oxygen. Ultraviolet rays can influence the survival rates of these microscopic organisms, by
affecting their orientation and mobility. This eventually disturbs and affects the entire
ecosystem.
25.
26.
27. . Impact on Plants
In some species of plants, UV radiation can alter the time of flowering, as well as the
number of flowers.
Plant growth can be directly affected by UV-B radiation. Despite mechanisms to
reduce or repair these effects, physiological and developmental processes of plants are
affected
Observation: Another observation is an increase in the ozone present in the
lower atmosphere due to the decrease in the ozone in the stratosphere. Ozone
present in the lower atmosphere is mainly regarded as a pollutant and a
greenhouse gas, that can contribute to global warming and climate change.
However, researches have pointed out that the lifespan of lower atmospheric
ozone is quite less, compared to stratospheric ozone. At the same time,
increase in the level of ozone in the lower atmosphere can enhance the ability
of sunlight to synthesize vitamin D, which can be regarded as an important
beneficial effect of ozone layer depletion.
28.
29. Growing concern for ozone depletion led to the adoption of the Montreal
Protocol in 1987, in order to reduce and control industrial emission of
chlorofluorocarbons (CFCs). Such international agreements have succeeded to a
great extent in reducing the emission of these compounds. However, more
cooperation and understanding among all the countries of the world is required to
mitigate the problem. You too can do your bit to save the ozone. Use/buy more
recycled products, save energy, take public transport, and, most importantly,
spread awareness. Our individual efforts can go a long way in saving the Earth's
blanket.
