Ozone

TOPICS TO BE DISCUSSED
 What is Ozone?
 Types of Ozone.
 Effects of Ozone.
 Physical and Chemical Properties of Ozone.
 Source of Ozone.
 Ozone Depletion.
 Ozone Hole.
 Effects of Ozone Depletion.
 How can we protect Ozone?
 How can we protect ourselves?

Overview of Earth’s Atmosphere
An atmosphere is a layer or layers of gases surrounding a planet or other
material body of sufficient mass. The earth’s atmosphere is comprised of gases
consisting mostly of nitrogen and oxygen. It also contains lesser amounts of
argon, carbon dioxide, and many other trace gases.
From bottom to top, the layers are:
• The Troposphere
• The Stratosphere
• The Mesosphere
• The Thermosphere
• The Exosphere
Note: The different layers of the atmosphere have contrasting characteristics.

Ultraviolet Radiation
• Ultra-violet means “beyond violet” in
Latin since violet is the shortest
wavelength of visible light and UV
light is the next shortest. They are high
energy electromagnetic wave emitted
from the sun. It is made up of
wavelengths ranging from 100nm to
400nm.
• UV radiation include:
i. UV-A, the least dangerous form of
UV radiation, with a wavelength
range between 315nm to 400nm.
ii. UV-B with a wavelength range
between 280nm to 315nm.
iii. UV-C which is the most dangerous
between 100nm to 280nm. UV-C is
unable to reach Earth’s surface due
to stratospheric ozone’s ability to
absorb it.
Note:
• Shorter wavelength means higher frequency.
• Higher frequency means higher energy.

OZONE
Ozone (O3) is a highly reactive gas composed of
three oxygen atoms. It is both a natural and a
man-made product that occurs in the Earth's
upper atmosphere (the stratosphere) and lower
atmosphere (the troposphere). Depending on
where it is in the atmosphere, ozone affects life
on Earth in either good or bad ways.
Ozone is present in low concentrations
throughout the Earth's atmosphere. In total,
ozone makes up only 0.6 ppm (parts per million)
of the atmosphere.

PHYSICAL PROPERTIES
 Standard State:Gas
 Boling temperature: -111.9 °C
 Melting temperature: -195.5 °C
 Specific Gravity: 2.144
 Color: Colorless OR Pale Blue
 Odor: Pungent Smell
Liquid ozone
 Deep Blue and Strongly Magnetic.

REACTIVITY OF OZONE
 Why is ozone so reactive?
Ozone molecule has three oxygen atoms which share covalent bonds with each
other and is also bipolar. This property of ozone enables it to react with both polar
and covalent molecules.
Ozone is also a very powerful oxidizing agent than oxygen and oxidation with ozone
evolves more heat and usually starts at a lower temperature than oxidation with
oxygen.
Ozone is an unstable gas which, at normal
temperatures, decomposes to biatomic
oxygen. At elevated temperatures and in
the presence of certain catalysts such as
hydrogen, iron, copper and chromium, this
decomposition may be explosive.

TYPES OF OZONE
Stratospheric Ozone
Stratospheric ozone is formed naturally through the interaction of solar
ultraviolet (UV) radiation with molecular oxygen (O2). The "ozone layer“,
approximately 6 through 30 miles OR 10 through 50 km above the Earth's
surface, reduces the amount of harmful UV radiation reaching the Earth's
surface.

TYPES OF OZONE
Tropospheric Ozone
Ozone is also found much nearer the ground, in the troposphere, the lowest level
of Earth’s atmosphere. Unlike the ozone that occurs naturally in the stratosphere,
tropospheric ozone (what we breathe) is man-made.
It is an indirect result of air pollution
created by photochemical reactions
between two major classes of air
pollutants, volatile organic compounds
(VOC) and nitrogen oxides (NOx) which
are present in automobile exhaust and
emissions from factories and power plants.

EFFECTS OF OZONE
Effect of Ozone on Human Health:
1. Stratospheric ozone absorbs UV
light, reducing human exposure to
harmful UV radiation that causes skin
cancer and cataracts.
2. Tropospheric ozone, when inhaled,
reacts chemically with many
biological molecules in the respiratory
tract, leading to a number of adverse
health effects. This makes ozone a
potent respiratory hazard and
pollutant near ground level.

STRATOSPHERE OZONE
Ozone Layer
The ozone layer is mainly found in the lower portion of the stratosphere,
from approximately 20 to 30 kilometers (12 to 19 miles) above Earth,
though the thickness varies seasonally and geographically. It prevents the
harmful ultraviolet radiations of the sun from reaching the Earth's surface,
and benefits both plants and animals.
The ozone layer can absorb 97–99% of the Sun's medium-frequency
ultraviolet light (from about 200 nm to 315 nm wavelength).

STRATOSPHERE OZONE
SOURCE
Ozone in the Earth's stratosphere is created by ultraviolet light striking oxygen
molecules containing two oxygen atoms (O2), splitting them into individual oxygen
atoms (atomic oxygen). The atomic oxygen then combines with unbroken O2 to
create ozone, O3. When ultraviolet light hits ozone it splits into a molecule of O2 and
an atom of atomic oxygen, a continuing process called the ozone-oxygen cycle.
Note: Ozone absorbs UV
light during both production
and destruction processes.

STRATOSPHERE OZONE
Ozone Layer Depletion
Chlorofluorocarbons (CFCs), containing chlorine and/or bromine,
chemicals found mainly in spray aerosols are the primary culprits in ozone
layer breakdown. When CFCs reach the upper atmosphere, they are
exposed to ultraviolet rays, which causes them to break down into
substances that include chlorine. The chlorine reacts with the oxygen
atoms in ozone and rips apart the ozone molecule.
Note: One atom of
chlorine can destroy
more than a hundred
thousand ozone
molecules.

STRATOSPHERE OZONE
Ozone Hole
The ozone hole is an annual thinning of the ozone layer over Antarctica,
caused by stratospheric chlorine. Other more moderate thinnings have
also been called "ozone holes", such as that over the North Pole during
certain weather conditions.
Cause of the ozone hole:
The cause of the ozone holes is generally agreed to be CFC
(chlorofluorocarbon) compounds which break down due to ultraviolet
light and become free radicals containing chlorine high in the Earth's
atmosphere. These radicals then break down the ozone catalytically.
Ozone destruction due to chlorine radicals from CFCs can take place in
the gas phase, but occurs particularly rapidly on the surface of polar
stratospheric clouds (PSC).

STRATOSPHERE OZONE
 Why is an ozone hole formed only above Antarctica and
not over developed countries that emit a lot of CFCs?
CFCs gasses takes 6 to 7 years to move up to the stratosphere and the
wind spreads them all around the world. Extreme cold, a freezing vortex
wind, frozen stratospheric clouds and 6-months darkness over Antarctica,
all provides ideal conditions for Chlorine to break from the CFCs. The
Chlorine (or Bromine) gasses, then destroy the ozone during spring (Sep ti
Dec) and causes the formation of ozone holes above Antarctica more
than other places.

Effects Of Ozone Layer Depletion
 Harm to human health:
 Skin cancers, sunburns and premature aging of the skin.
 DNA absorbs UV-B radiation and changes its shape. This changes in the DNA results in
mutated cells or the cells die and then cancer.
Note: Scientific evidence suggests that 1% depletion in ozone layer results in 5% increase in skin cancer.

 Cataracts, blindness and other eye diseases.
 Weakening of the human immune system

Damage to marine life
In particular, plankton (tiny organisms in
the surface layer of oceans) are
threatened by increased UV radiation.
Plankton are the first vital step in aquatic
food chains.

 Animals
 In domestic animals, UV overexposure may cause eye and skin cancers. Species
of marine animals in their developmental stage (e.g. young fish, shrimp larvae and
crab larvae) have been threatened in recent years by the increased UV radiation
under the Antarctic ozone hole.
 Materials
 Wood, plastic, rubber, fabrics and many construction materials are degraded by
UV radiation.
 The economic impact of replacing and/or protecting materials could be
significant.

PROTECT THE ENVIRONMENT
 What You Can Do about Ozone Layer Depletion?
 Established policies that prevent future use of certain
types of chemicals.
 Know the rules: It is illegal to recharge refrigerators,
freezers and home/vehicle air conditioners with CFCs.
 If you have an older refrigerator or an older vehicle with
an air conditioner, have it serviced by a qualified
technician, and make sure the CFC is recaptured and
recycled by technician who is specifically certified to do
this work.
 Don't buy or use portable fire extinguishers that contain
 Halogens
 Chlorofluorocarbons (CFCs)
 Carbon tetrachloride
 Methyl chloroform
 Hydrochlorofluorocarbons (HCFCs)

PROTECT YOURSELF
Protect Yourself from Ultraviolet Radiation
 There's no such thing as a "healthy tan”. Fair-skinned
people are particularly vulnerable to UV
radiation, as are infants and children but
everyone should be careful.
 Be aware that UV radiation is most intense during
the summer, so take extra precautions. So sit in
the shade, and avoid prolonged exposure when
the sun is high especially between 10 a.m. and 4
p.m.
 Wear protective clothing and a broad-brimmed
sunhat. Sunglasses with 100% UV protection are
also important.

Ozone

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Ozone