OZONE LAYER
It is the layer in Earth's atmosphere that consists of high
concentrations of Ozone ( O3 ). The Ozone layer is mainly found in the lower
portion of the stratosphere approximately 20-30 kilometers (12 to 19 mi) above
the earth.
The Ozone occurs within the Stratosphere layer when the
diatomic oxygen reacts with the energy associated with the light from the sun.
The diatomic oxygen rapidly absorbs ultraviolet (UV) light with the wavelengths
between 70-250 nanometers (nm). The O2 gas
presented above the stratosphere filters and absorbs the O2 gas and other gas
molecules in the stratosphere. Hence, no UV light with wavelength shorter than
220 nm reaches the Earth's surface, this protects us form the harmful damage
that these wavelengths of the sun produces.
When UV light (in the form of photons) with wavelength more than 240 nm is absorbed
by the diatomic oxygen, the energy is gained to split the O2 gas into two
oxygen atoms. When one of the energized long oxygen atom collides with another
molecule of O2 gas, Ozone (O3) is formed and heat is let off.
The Formation of Ozone
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picture found at http://astrobioloblog.wordpress.com/2011/08/18/life-in-our-solar-system-%E2%80%93-earth/
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Ozone is really good when it comes to absorbing UV light
different from that of diatomic oxygen because of its molecular energy level
more likely than that of the sunscreen
worn to protect your skin from sun. Wavelength between 220-290 nm is absorbed
almost fully by the stratosphere's ozone layer. This expanse of wavelengths
absorbed by ozone coincides with the UV-C region of wavelengths of 200 to 280
nm. Ozone is partially effective in shielding the Earth's surface from UV-B
wavelengths (280 to 320 nm) and completely ineffective in shielding from UV-A
wavelengths (320 to 400 nm), though these ranges of ultraviolet light are the
least harmful to biological life.
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Description Diagram illustrating the ozone-oxygen cycle NOTE:
the text in the final version can't be modified but earlier versions can be if you wish to translate them.
Date 2010-01-27 20:56 (UTC)
Source Ozone_cycle.jpg
Author Ozone_cycle.jpg: created by
derivative work: Smartse (talk) |
Ozone Depletion
Earth is protected
by the Ozone layer from the harmful ultraviolet rays sent down by the sun. If
Ozone layer is depleted by human activities, the effect on the planet would but
catastrophic .
Although, the
concentration of ozone in the stratosphere naturally increases and decreases
with things like altitude, temperature, and weather, the considerable level of
ozone reduction is not due to only natural factors. Synthetic chemicals and
gases like free radical catalysts, including nitric oxide (NO), nitrous oxide
(N2O), hydroxyl (OH), atomic chlorine (Cl), and atomic bromine (Br) play a huge
role in ozone depletion. Aerosols and chlorofluorocarbons (CFCs) have been
found to be largely responsible for the depletion of the ozone layer. The
reduction of the ozone layer presents a large risk for many chemical and
biological processes on the Earth's surface. Exposure to radiation that is
usually shielded by the ozone layer has a variety of damaging effects on living
organisms.
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Ozone depleted
http://www.esu.edu/~scady/parise/3reactions.htm |
Ozone Depletion in Ozone Scarce Regions
Depletion of ozone also happens in the oxygen atom scare
region in the lower ozone layer. It is when no free oxygen to complete the catalytic
process, two catalysts break down two ozone molecules creating two oxygenated
molecules and two molecules of O2 gas. Hence, in this case catalytic process, two
ozone molecules react with two catalysts to produce three molecules of diatomic
oxygen.
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| Ozone Depletion without Atomic Oxygen |
Synthetic Chemical Processes of Ozone Depletion and CFCs
The most well known contributors to ozone depletion are chlorofluorocarbons (CFCs). CFCs are hydrocarbons where either some or all of the hydrogen atoms have been substituted by fluorine and chlorine atoms. These chemicals used frequently as refrigerants and, until lately, as propellants in aerosols. When chlorofluorocarbons are released into the air, they rise into the atmosphere where they react with ultraviolet light. In the reaction, the CFC molecules break down into atoms and smaller molecule fragments that act as ozone depleting catalysts. CFCs significantly increase ozone depleting processes in the Earth’s atmosphere. The molecule fragments containing chlorine atoms go through a sequence of decomposition reactions that increase the amount of stratospheric chlorine.
Chlorine atoms, as mentioned before, are highly reactive. These atoms undergo many forms of reactions that deplete ozone in the process. Methyl chloride gas (CH3Cl) decomposes when it reacts with ultraviolet light, similarly to CFCs, or can react with an OH radical. Chlorine atoms are extremely efficient ozone depleting catalysts; a single atomic chlorine is responsible for the destruction of tens of thousands of ozone molecules.
(Taken from http://www.esu.edu/~scady/parise/3reactions.htm)
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Chlorine Acting as a Catalyst
picture found at http://www.learner.org/courses/envsci/visual/visual.php?shortname=ozone_depletion |
Ozone Hole
A huge concern in the depletion of the ozone layer is the creation of ozone holes. An ozone hole is described as an extreme decrease in the amount of atmospheric ozone, measured in Dobson units (DU), which lies over the Earth. One DU is the equivalent to 0.001 cm thickness of pure ozone at standard conditions (1 atmosphere and 0°C) (10). The most acute case of seasonal ozone depletion is known as the Antarctic Ozone Hole. The hole occurs at a seasonal standpoint in an area where there is almost no oxygen atoms present in the stratosphere. The major destructive element in these conditions is chlorine atoms in the reaction of two chlorine monoxide molecules.
The Antarctic Ozone Hole
In Antarctica, the increase of active chlorine is enlarged by the existence of polar stratospheric clouds. Usually, clouds do not form in the stratosphere because of the temperature inversion; however, because of the extremely low temperatures in the Antarctic region, water and nitric acid condense to materialize ice clouds, called polar stratospheric clouds. The polar stratospheric clouds reduce the concentration of oxygen containing molecules and nitrogen gas molecules. The rate of conversion of chlorine oxide to the relatively inert chlorine nitrate in the reaction is dramatically slowed, leaving the active, catalytic chlorine atoms to inflict extreme devastation to the ozone layer.
The size and ozone thickness of the Antarctic Ozone Hole has fluctuated throughout the years, resulting in a wide range of UV exposed area and ultraviolet light intensities at ground level. The amount of UV-B radiation reaching the Antarctic grounds in the spring, when the sun is highest in the sky with the lowest ozone concentrations, increases by a factor of 3 to 6. Consequently, springtime in Antarctica is the most dangerous in terms of UV levels for biological life.
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HARMFUL EFFECT
Impact on the Ocean
Ozone depletion results in increased ultraviolet-B (UV-B) doses at all depths of the seas and oceans, there by extending the depth to which higher than ambient levels of biologically effective radiation penetrate. Studies conducted on the effects of UV-B on aquatic ecosystems have focused on the Antarctic region, where the largest losses of ozone have been measured. UV-B is known to affect adaptive strategies in phytoplankton, cause damage in DNA and proteins, and affect organisms in their developmental stages. These direct effects may lead to indirect effects, such as decreased primary productivity, changes in biodiversity, decreased nitrogen uptake by microorganisms, and reduced capacity for oceans to fix carbon dioxide.
NAS, a NASA research website reports that phytoplankton in arctic areas are more susceptible to the harmful effects of UV light radiation. A field survey of Antarctic phytoplankton near the springtime ozone hole found a 6 to 12 percent drop in phytoplankton productivity.UV light causes plankton to sink to deeper depths of the ocean, which inhibits their reproduction and growth rate.
Global Warming
Global warming isn't the direct cause of ozone depletion, but they share many similarities. The man-made CFCs like Freon are mostly responsible for the depletion of the ozone layer. The gases may also act as a greenhouse gas that traps the heat on earth, but to a lesser degree. Many gases that heat up the earth also tear down the ozone layer. In addition, CFCs may still influence the ozone because those gases stay in the atmosphere for a long time. According to the U.S. Environmental Protection Agency, the ozone will return to normal levels by 2050. This is good news, but it won't necessarily influence the rate of global warming.
Ozone is actually a greenhouse gas, contributing to trapping heat in the stratosphere. If the ozone layer depletes, it affects the temperature of the earth. The depletion contributes to a global cool down and significant weather changes in higher areas near the stratosphere.
Impact on land plants
Plants exposed to elevated UV radiation can tolerate reduced growth; less than satisfactory development can have a direct effect on food crops. Broad-leafed plants seem to show the most susceptibility over woody plants or grass varieties to UV damage. Plants, animals and microbes in cold ecosystems of the world appear to suffer persistent damage after overexposure to UV radiation, according to the U.S. Global Change Research Information Office. The foliage often shows reduced leaf sizes and shorter stems.
Increase Effect on Air Pollution
Ozone is gradually being destroyed by man-made chemicals referred to as ozone-depleting substances, including chlorofluorocarbons, hydrochlorofluorocarbons, and halons. These substances were formerly used and sometimes still are used in coolants, foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants. Thinning of the protective ozone layer can cause increased amounts of UV radiation to reach the Earth, which can lead to more cases of skin cancer, cataracts, and impaired immune systems. UV can also damage sensitive crops, such as soybeans, and reduce crop yields.
Effects to Human
i)Skin
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| skin cancer |
One of the most common effects of UV exposure is "erythema", also known as sunburn. Sunburn occurs when skin cells are damaged by the absorption of energy from UV rays. To compensate for this injury, the skin sends extra blood to the damaged skin in an attempt to repair it,thus accounting for the redness that is associated with sunburn. The amount of time it takes for a sunburn to occur is dependent mostly on the relative amounts of UV rays that are hitting the skin, and on a person's skin type. People with naturally dark skin already have inherently high levels of melanin, and so are able to spend a longer amount of time in the sun before burning, if they burn at all. Fair-skinned people don't have it quite so easy burning can occur within a relatively short amount of time.
Another effect of ultraviolet rays on the skin is photoaging. Recent studies have shown that many of the symptoms commonly associated with mere aging (i.e. wrinkles, loosening of the skin) may instead be related to UV exposure so though your tan may look good now, you could be paying your dues in wrinkles later.
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| squamous-cell-carcinoma |
ii)Skin Cancer
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| Symptom of skin cancer |
“ Ultraviolet (UV) irradiation present in sunlight is an environmental human carcinogen. The toxic effects of UV from natural sunlight and therapeutic artificial lamps are a major concern for human health. The major acute effects of UV irradiation on normal human skin comprise sunburn inflammation erythema, tanning, and local or systemic immunosuppression. ”
— Matsumura and Ananthaswamy , (2004)
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| UV effect in deferent way |
UVA, UVB, and UVC can all damage collagen fibers and, therefore, accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage. In the past, UVA was considered not harmful or less harmful, but today it is known it can contribute to skin cancer via indirect DNA damage (free radicals and reactive oxygen species). It penetrates deeply, but it does not cause sunburn. UVA does not damage DNA directly like UVB and UVC, but it can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. Accordingly the DNA damage caused indirectly to skin by UVA consists mostly of single-strand breaks in DNA, while the damage caused by UVB includes direct formation of thymine dimers or other pyrimidine dimers, and double-strand DNA breakage. UVA is immunosuppressive for the entire body (accounting for a large part of the immunosuppressive effects of sunlight exposure), and UVA is mutagenic for basal cell keratinocytes in skin
iii)Effects on Eyes
Ultraviolet rays can be reflected towards the eyes by certain substances, such as sand and snow. When this happens, the amount of UV rays the eyes are exposed to is increased. This fact is the basis of the condition photokeratitis, also known as snow blindness. Photokeratitis is a sunburn of the cornea, and usually recedes within one to two days. It occurs when the eyes are exposed to large quantities of UV light in a short amount of time. The reflection of UV rays off of snow and sand are enough to incur this injury.
It is more difficult to isolate the exact amount of damage that UV imposes on the eye over a long period of time, as the body has its own built-in defense against harmful rays. If you were to try to look up at the sun, you would find that you would not be able to do so for any length of time. Your eyes would naturally start to close. This effect is also noticed on especially bright days, displayed in the form of squinting. What is known, however, is that cumulative exposure to UV rays is one of the causes of opacity of the eye's lens, called cataract, a condition that displays itself primarily in elderly people, and results in blurred and fuzzy vision.
Save the Earth from Ozone Depletion
To raise consciousness is the first step to begin protecting our damaged ozone layer.
Every one should be responsible for the use and abuse of certain products that have a negative effect on nature.There are many and simple ways in which we can save our ozone layer. With these simple rules we can create a chain of consciousness that will make manufactures stop creating non-environmentally friendly products.
*Avoid buying and using aerosols and sprays composed of chlorofluorocarbon (CFC).
*Avoid using fire extinguishers with halogenated hydrocarbon since it is a very aggressive substance for the ozone layer.
*Avoid buying insulating material made up of CFC. Instead you can use dark chipboard cork that performs the same function and does not contaminate the environment.
*Maintain air-conditioning clean because if they do not function properly, they Emmit CFC to the atmosphere.
*Check the freezer and car air-conditioning. If they do not function properly, have them repair because they may have leaks.
*Opt to buy a refrigerator or an air-conditioning without CFC.
*Report whether you know that products with bromomethane are used in some sown fields and crops because these substances are contaminating.
Other actions that help reduce air pollution:
*Reduce the use of your car and of other gadgets like compressors, lawn mowers, etc.
*Arrange an itinerary to save time and money if you have to use your car.
*Use alternative means of transport: buses, bicycles, or simply walk.
*Reduce the use of heating and air-conditioning.
*Buy energy saving gadgets and bulbs. You will reduce levels of pollution and money.
All of us can contribute to the protection of the environment. Before demanding politicians to implement policies to protect the ozone layer, let’s begin ourselves doing something for the environment.
Reference
1.http://www.esu.edu/~scady/parise/3reactions.htm
2.http://en.wikipedia.org/wiki/Ozone_depletion#Observations_on_ozone_layer_depletion
3.http://en.wikipedia.org/wiki/Ozone_layer
4.http://www.livestrong.com/article/90618-ultraviolet-light-affect-humans/
5.http://uv.biospherical.com/student/page4.html
6.http://www.ciesin.org/TG/OZ/aqecosys.html
7.http://www.ehow.com/facts_6154004_uv-light-affect-ocean_.html
8.http://www.ehow.com/how-does_5112209_global-warming-effects-ozone-depletion.html
9.http://en.wikipedia.org/wiki/Air_pollution
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