Transcript Ozone and the Ozone Hole

Ange Darnell
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Ozone is a relatively
unstable molecule made
up of three oxygen atoms.
The majority of this
compound exists in the
stratosphere (15 miles up)
and shields the Earth from
harmful UV radiation from
the sun.
Source: University of Alaska
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Ozone also naturally exists at the Earth’s surface
(troposphere); ozone is a natural component of the clean
atmosphere.
However, excess ozone formed in the troposphere by human
activities is a harmful pollutant: dangerous to health, a major
constituent of smog, and a greenhouse gas. This is known as
“bad” ozone.
Source: theozonehole.com
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Ozone in the troposphere is produced when sunlight and heat
react with nitrous oxides and volatile organic compounds,
known as ozone precursors.
These pollutants are emitted by vehicles, power plants,
refineries, and chemical plants.
The amounts of “good” and “bad” ozone in the atmosphere
depend on a balance between processes that create and
destroy ozone; an upset in this balance has serious
consequences for life on Earth.
Source: EPA
Source: NASA
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Halogen source gases are emitted at the Earth’s surface by human
activities and natural processes
These gases accumulate in the atmosphere because they are
unreactive and do not dissolve readily in rain or snow, and are
distributed throughout the lower atmosphere by winds
The gases are then transported to the stratosphere by air motions
They are then converted to reactive halogen gases in chemical
reactions involving UV radiation from the sun
These radicals catalyze the breakdown of ozone into O and O2
A catalytic reaction cycle is a set of chemical reactions which result
tin the destruction of many ozone molecules while the molecule
that started the reaction is reformed to continue the process
A single CFC molecule can destroy up to 100,000 ozone molecules
The very thing that makes ozone good for filtering UV radiation
makes it easily destroyed: it is very unstable
Source: EPA and theozonehole.com
man-made
CFCs
man-made
man-made
CFCs
man-made
CFCs
man-made
Source:theozonehole.com
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Chlorofluorocarbons were developed in the 1930s as a safe,
non-toxic, non-flammable alternative to dangerous
substances for refrigeration and spray can propellants.
Very little chlorine exists naturally in the atmosphere and
CFCs are an excellent way of introducing chlorine into the
ozone layer.
They have been used extensively as aerosol-spray
propellants, refrigerants, solvents, and foam-blowing agents.
CFCs have a lifetime in the atmosphere of 20 to 100 years, so
their effect lasts for a long time, even after their use
decreases.
Source: theozonehole.com
Source: FDA
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Bromine is another important contributor to ozone
depletion.
Bromine is a “halon” (halogenated hydrocarbon gas) and
is used for fire extinguishers, protection of large
computers, military hardware and commercial aircraft. It
is also used a s an agricultural fumigant.
There are also natural sources of chlorine and other
ozone destroying compounds, such as volcanic
eruptions, and those emitted by oceanic and terrestrial
ecosystems.
However, only a fraction of these emissions reach the
stratosphere because they are rapidly removed by
rainfall and other natural processes.
“Changes in the natural sources of chlorine and bromine
since the middle of the 20th century are not the cause of
observed ozone depletion”
Source: EPA
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Although chlorine emitted from CFCs has a
longer atmospheric lifetime than bromine
sources, the bromine has a 7 to 16 times
greater ozone depletion potential than
chlorine.
A common misconception is that CFCs and
other halogen source gases will never reach
the stratosphere because they are “heavier
than air.”
However, the distribution of gases in the
troposphere and stratosphere are not
controlled by the molecular weight of the
gases because air is in continual motion as a
result of winds and convection.
Source: EPA
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The ozone hole appears above Antarctica in the
spring, from September to early December.
Polar stratospheric clouds (PSCs) form during the
winter, due to extreme cold.
The extreme cold is due to the fact that there are 3
months without sunlight as well as the “polar vortex”
trapping and chilling the air.
These extremely low temperatures cause cloud
particles to form that are composed of either nitric
acid or ice, which provide surfaces for chemical
reactions that lead to ozone destruction
Sunlight is required for the chemical reactions to take
place, which is why even though PSCs are most
abundant during winter, the hole does not form until
the spring.
Source: theozonehole.com
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While ozone is only a minority constituent of
the atmosphere, it is responsible for the
majority of UVB absorption.
Without this absorption, UV can damage
crops, plankton and human health.
Many economically important species of
plants, such as rice, depend of cyanobacteria
which reside in their roots to retain nitrogen.
These cyanobacteria are sensitive to UV
radiation.
Source:
theozonehole.com
and Wikipedia
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The Southern Ocean is one of the world’s most productive
marine ecosystems, and is a major supplier of nutrients
carried to other parts of the world by undersea currents.
The phytoplankton in these oceans capture the sun’s
energy through photosynthesis, providing food for
microscopic animals.
They are then eaten by krill, which in turn sustain the
Antarctic’s seals, penguins and whales.
Plankton are extremely susceptible to effects of UV light,
and a decrease means less food for these marine animals,
which would eventually lead to a loss of approximately 7
million tons of fish per year.
With the human food supply already strained because of
increasing population, small reductions due to UV damage
may be disastrous, especially to third world countries.
Source:
theozonehole.com
and Wikipedia
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UV radiation can produce radicals that are very reactive and
cause damage by oxidizing biological molecules, such as DNA.
Skin cancer rates increase and the number of deaths related to
skin cancer also increase. “An estimated 10% reduction in the
ozone layer will result in a 25% increase in skin cancer rates for
temperate latitudes by the year 2050.”
Skin damage could lead to other health issues because skin in
the immune system’s largest defense, which would leave the
body vulnerable to many diseased cause by bacteria and viruses
entering through the skin.
Increased exposure to UV has been linked to greater risk of the
herpes virus, HIV-1, papilloma viruses, malaria, forms of TB,
leprosy, dermatitis, and E. coli.
In addition, since UV rays readily damage DNA, this could play
another role in the mutation of existing disease bacteria and
viruses, possibly producing totally new strains of pathogens
UV rays can also harm the cornea
Source: EPA and
theozonehole.com
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Although the releasing of ozone depleting
chemicals into the atmosphere is at or near its
peak, the stratosphere lags behind the surface by
several years.
Complete recovery of the ozone is not expected
to occur until the late 21st century, and this
precludes a cessation of ozone depleting
chemicals being released by human activities.
Assuming full compliance with the Montreal
Protocol, the ozone layer will begin to recover in
future decades.
Source: EPA and wikipedia
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Although climate change is not the cause of the ozone hole (or
vice versa), it could have future consequences regarding its
recovery or further ozone depletion.
Global warming from CO2 and other greenhouse gases
(including tropospheric ozone) is expected to heat the
troposphere and cool the stratosphere. This decrease in
temperature will increase ozone depletion and the frequency of
ozone holes.
Conversely, ozone depletion is a radiative forcing of the climate
system. Reduced ozone will cause the stratosphere to absorb
less solar radiation, which further cools the stratosphere and
heats the troposphere, further contributing to climate change.
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Ozone and climate change are also linked
indirectly because both ozone-depleting
gases and substitute gases contribute to
climate change.
Chlorine-containing gases have a significant
importance for ozone depletion and have a
high global warming potential.
Bromine-containing gases have a high ozone
depleting potential and a relatively high
global warming potential.