This presentation is about Ozone Layer and chemicals known to cause its depletion. It also covers information about Ozone Hole and Correlation between Ozone depletion and skin diseases due to Ultra Violet light.It also contains no. of ways to limit ozone deterioration.

2. Ozone (O3) is a highly-reactive from of oxygen.
 Unlike oxygen (O2), ozone has a strong scent and is
blue in color.
 Ozone exists within both the tropospheric and
stratospheric zones of the Earth’s atmosphere
 In the troposphere, ground level ozone is a major air
pollutant and primary constituent of photochemical
smog
 In the stratosphere, the ozone layer is an essential
protector of life on earth as it absorbs harmful UV
radiation before it reaches the earth.
 It is a toxic, irritating gas, often encountered in
surface air pollution episodes, when it can trigger
asthma and irritate mucous membranes.


3. 
Ozone is a compound of oxygen that contains three atoms
instead of the two found in the oxygen gas that sustains life. It
was discovered in 1839 by a Swiss chemist, Christian
Friedrich Schonbein.

Ozone concentrations at the surface were first measured
reliably by Robert Strutt (later 4th Lord Rayleigh) in 1918
using spectra of a hydrogen lamp recorded through five
kilometers of air. Dry air consists of 78% nitrogen and 21%
oxygen and there are normally trace amounts of other
gases, principally argon, water and carbon dioxide, present.
The concentration of ozone is usually only a few parts per
million and even in the ozone layer it is only one part in
100,000.

6. Over the last 50 years we have
introduced chemicals into the
atmosphere that are capable of
destroying ozone through photochemical
processes. Chloro-fluoro-carbons (CFCs)
are widely known, but there are also
other ozone depleting substances such as
halons (bromo-fluoro-carbons) and
methyl bromide.Chlorofluorocarbons are
created and used in refrigerators and air
conditioners. These chlorofluorocarbons
are not harmful to humans and have
been a benefit to us. Once released into
the atmosphere, chlorofluorocarbons
are bombarded and destroyed by
ultraviolet rays. In the process chlorine
is released to destroy the ozone
molecules.

7.  Molecular oxygen is broken down in the stratosphere by solar
radiation to yield atomic oxygen, which then
combines
with molecular oxygen to produce ozone. The ozone is then
destroyed by chlorine atoms.

10. There are many ozone hole depleting substances present
in our atmosphere which can react with ozone to turn it
back into oxygen. In most parts of the world the reactions
are very slow and there is little damage to the ozone
layer, however over the Antarctic a dramatic hole opens in
the ozone layer every spring and fills in again by midsummer.

11. The answer is essentially 'because of the weather in the ozone
layer'. In order for rapid ozone destruction to happen, clouds have to
form in the ozone layer. In these clouds surface chemistry takes
place. This converts chlorine or bromine (from CFCs and other
ozone depleting chemicals) into an active form, so that when there is
sunlight, ozone is rapidly destroyed. Without the clouds, there is
little or no ozone destruction. Only during the Antarctic winter does
the atmosphere get cold enough for these clouds to form widely
through the centre of the ozone layer. Elsewhere the atmosphere is
just too warm and no clouds form. The northern and southern
hemispheres have different 'weather' in the ozone layer, and the net
result is that the temperature of the Arctic ozone layer during winter
is normally some ten degrees warmer than that of the Antarctic. This
means that such clouds are rare, but sometimes the 'weather' is
colder than normal and they do form. Under these circumstances
significant ozone depletion can take place over the Arctic, but it is
usually for a much shorter period of time and covers a smaller area
than in the Antarctic.

13. Some reports in the media suggest that the ozone layer over Antarctica is now
recovering. This message is a little confused. Recent measurements at surface
monitoring stations show that the loading of ozone destroying chemicals at the
surface has been dropping since about 1994 and is now about 6% down on that peak.
The stratosphere lags behind the surface by several years and the loading of ozone
depleting chemicals in the ozone layer is at or near the peak. Satellite measurements
show that the rate of decline in ozone amount in the upper stratosphere is
slowing, however the total ozone amount is still declining. The small size of the 2002
ozone hole was nothing to do with any reduction in ozone depleting chemicals and it
will be a decade or more before we can unambiguously say that the ozone hole is
recovering. This assumes that the decline in ozone depleting chemicals continues and
that there are no other perturbations to the ozone layer, such as might be caused by a
massive volcanic eruption or Tunguska like event. It will be the middle of this century
or beyond before the ozone hole ceases to appear over Antarctica. What we saw in
2002 is just one extreme in the natural range of variation in the polar stratosphere
and is the equivalent of an extreme in 'stratospheric weather'. By contrast the
'weather' in 2003 moved to the opposite extreme and we saw one of the largest
ozone holes on record.

14. The ozone hole is a completely different phenomenon
to global warming, however there are links between
them. The ozone hole is caused by ozone depleting
chemicals in the atmosphere, which have been produced
by industry, for example CFCs. One link is that CFCs are
also 'greenhouse gasses'. Enhanced global warming is a
probable consequence of increasing amounts of
'greenhouse gasses', such as carbon dioxide and
methane, in the atmosphere. Although the surface of the
earth warms, higher up the atmosphere cools, thus
increasing the area where stratospheric clouds can form.
This makes a larger area susceptible to ozone depletion
and provides another link between the two issues.

15.  UV
radiation from the
sun releases the radicals
Cl and ClO.
 Ozone is a highly
unstable molecule so it
readily donates its extra
oxygen molecule to free
radical species such as
hydrogen, bromine, and
chlorine.
 These compound
species act as catalysts
in the breakdown of
ozone molecules.

16. Ozone depletion causes increases in UV rays’s
effects on aquatic ecosystems by:
1. decreasing the abundance of phytoplankton –
affects the food stock for fishes and the
absorption of CO2.
2. decreasing the diversity of aquatic organisms –
reduces food stock and also destroys several
fish and amphibians.

17.  Skin cancer:
UV radiation is the primary cause of
skin cancer .When UV light damages DNA , it impairs
its ability to control skin growth.
 Other skin problems: Overexposure to UV light can
lead to skin effects that resemble premature aging.
 Immune suppression: Evidence suggests that the
body's immune system will begin to weaken as a
result of too much UV light.
 Eye problems: Cataracts can develop from UV
exposure, and can lead to blindness.

19.  Clouds cover - partly cloudy days do little to
reduce
UV exposure but rainy or substantially overcast days
reduce UV exposures.
 The time of
day – peak exposure time is 12:00 noon
- 1:00 p.m. UV intensity is reduced by about half at
three hours before and three hours after the peak
exposure time.

20. 



Encourage growth of plants that produces oxygen, and
discourage deforestation
Eliminate production and release of known ozone depleting
chemicals (such as CFCs and HCFCs) where remotely possible.
An easy way to help combat ozone deterioration is to limit the
amount of driving. Motor vehicles produce quantities of
emissions which help to create smog. Smog is a leading factor
with regard to ozone deterioration.
Another easy way to help prevent ozone deterioration is to
use environmentally friendly cleaning products. There are
many non-toxic, non-ozone depleting cleaning supplies.

21. On an international scale, banning
the use of CFC will slow down the
destruction of ozone. This is being achieved
by through the Montreal Protocol, an
international agreement to reduce the use
of CFCs and eventually ban them completely.
CFCs have now been banned in more
economically developed countries.
However, in some less economically
developed countries CFCs are still being
used due to the high cost of replacing it with
a more ozone friendly substance.
The efforts seem to be working.
Reports show that by 2049, the ozone will
recover to 1979 thickness, which is when
scientists believe the hole began to form.
Many scientists believe the Montreal
Protocol is responsible for this joyous
recovery.

22. THE END