A free chlorine atom reacts with an ozone molecule (O3) and forms chlorine monoxide (ClO) and a molecule of oxygen. Now chlorine monoxide 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 the result is the reduction or depletion of ozone in the stratosphere.
UV-B radiation (280- to 315- nanometer (nm) wavelength) from the Sun is partially absorbed in this layer. As a result, the amount of UV-B reaching Earth’s surface is greatly reduced. UV-A (315- to 400-nm wavelength) and other solar radiation are not strongly absorbed by the ozone layer. Human exposure to UV-B increases the risk of skin cancer, cataracts, and a suppressed immune system. UV-B exposure can also damage terrestrial plant life, single cell organisms, and aquatic ecosystems.
Effects on Marine EcosystemsPhytoplankton form the foundation of aquatic food webs. Phytoplankton productivity is limited to the euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support net productivity. The position of the organisms in the euphotic zone is influenced by the action of wind and waves. In addition, many phytoplankton are capable of active movements that enhance their productivity and, therefore, their survival. Exposure to solar UVB radiation has been shown to affect both orientation mechanisms and motility in phytoplankton, resulting in reduced survival rates for these organisms. Scientists have demonstrated a direct reduction in phytoplankton production due to ozone depletion-related increases in UVB. One study has indicated a 6-12% reduction in the marginal ice zone.Solar UVB radiation has been found to cause damage to early developmental stages of fish, shrimp, crab, amphibians and other animals. The most severe effects are decreased reproductive capacity and impaired larval development. Even at current levels, solar UVB radiation is a limiting factor, and small increases in UVB exposure could result in significant reduction in the size of the population of animals that eat these smaller creatures.
Effects on Human HealthLaboratory and epidemiological studies demonstrate that UVB causes nonmelanoma skin cancer and plays a major role in malignant melanoma development. In addition, UVB has been linked to cataracts -- a clouding of the eye’s lens. All sunlight contains some UVB, even with normal stratospheric ozone levels. It is always important to protect your skin and eyes from the sun. Ozone layer depletion increases the amount of UVB and the risk of health effects.EPA uses the Atmospheric and Health Effects Framework (AHEF) model, developed in the mid 1980s, to estimate the health benefits of stronger ozone layer protection policies under the Montreal Protocol. EPA estimates avoided skin cancer cases, skin cancer deaths, and cataract cases in the United States.Protecting the Ozone Layer Protects Eyesight – A Report on Cataract Incidence in the United States Using the Atmospheric and Health Effects Framework Model (68 pp, 1.52 MB, About PDF) This 2010 peer-reviewed EPA report shows the AHEF model’s capability to estimate avoided cataract incidence, due to improved spatial resolution and information on the biological effects of UV radiation. A one page fact sheet summarizes the background, key findings, and future research topics for the AHEF model on UV radiation and cataracts.Human Health Benefits of Stratospheric Ozone Protection (PDF) (83 pp, 1.2 MB, About PDF)This 2006 peer-reviewed report describes the analytical and empirical methodologies used by the AHEF model.
Siminari pollution.(ozone layer depletion)
• The atmosphere is a layer of gases which surrounds the entire Earth. The purpose of this "layer" around the Earth is to prevent excessive amounts of radiation from reaching the Earth to survive a planet. The atmosphere is divided into; I. Troposphere. II. Stratosphere. III. Mesosphere. IV. Thermosphere.
•This is the upper limit ofour atmosphere.•A layer is also where thespace shuttle orbits.•Meteors or rockfragments burn up in it.•Many jet aircrafts fly in it,because it is very stable.Also, the ozone layer absorbsharmful rays from the Sun.• The first layer above thesurface and contains halfof the Earths atmosphere.
is a colorless gas, it relatively simple molecule,consisting of three oxygen atoms bound together. is a highly-reactive from of oxygen, Near theEarth‘s surface, hurt plant life, and damage people‘slung tissues. is a gas that occurs naturally in our atmosphere.Most of it is concentrated in the ozone layer, a regionlocated in the stratosphere several miles above thesurface of the Earth. also plays a vital role by shielding humans andother life from harmful ultraviolet ―ultraviolet B‖, light
• The ozone layer is a deep layer and concentration of ozone molecules in the stratosphere, encircling the Earth.• The ozone layer is a belt of naturally occurring ozone gas that sits ‗‘15 to 30 kilometers‘‘ above.• About 90% of the planets ozone is in the ozone layer.• While stratospheric ozone, which protects us from the sun.
when short-wavelength UVlight from the sun hits a moleculeof oxygen gas. The light has somuch energy that it breaks theoxygen bond holding the atomstogether, thus creating twooxygen atoms. Through thisprocess, the oxygen essentiallyabsorbs the short-wavelength UVlight, but this still leaves asignificant amount of UV lightwith longer wavelengths, which iswhere ozone comes in.
Destruction of the stratospheric ozone layer. This destruction of ozone is caused by the breakdown of certain chlorine and/or bromine containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules.A worrying rate of ozone depletion is foundabove the Arctic. Stratospheric clouds in the Arctic
• The Antarctic ozone hole was discovered in 1985 by British scientists Joesph Farman, Brian Gardiner, and Jonathan Shanklin of the British Antarctic Survey.• The ozone "hole" is really a reduction in concentrations of ozone high above the earth in the stratosphere. The ozone hole has steadily grown in size (up to 27 million sq. km.
• Human actions can change the natural state of our climate:• The world community works together in a targetted way, global environmental problems can be effective.• Cfcs are just one class of chemical substance that depletes the ozone layer, but they are the most important one.
halogen source gases are emitted atearth‘s surface by human activities and naturalprocesses. halogen source gases accumulatein the atmosphere and are globally distributedthroughout the lower atmosphere by winds andother air motions. halogen source gases are transportedto the stratosphere by air motions.
most halogen gases are converted inthe stratosphere to reactive halogen gases inchemical reactions involving ultravioletradiation from the sun. reactive halogen gases causechemical depletion of stratospheric ozone overthe globe. air containing reactive halogen gasesreturns to the troposphere where the gases areremoved by moisture in clouds and rain.
• The cause of ozone depletion is the in the level of such as hydroxyl radicals, nitric oxide radicals and atomic and .• The most important compound, which accounts for almost 80% of the total depletion of ozone in the stratosphere are chlorofluorocarbons (CFC).
• chlorofluorocarbons (CFC).• These compounds are very stable in the lower atmosphere of the Earth, but in the stratosphere, they break down to release a free chlorine atom due to ultraviolet radiation.• When CFCs and HCFCs reach the stratosphere, the ultraviolet radiation from the sun causes them to break apart and release chlorine atoms which react with ozone, starting chemical cycles of ozone destruction that deplete the ozone layer.• One chlorine atom can break apart more than 100,000 ozone molecules.
• Measurements of CFCs in the stratosphere are made from balloons, aircraft, and satellites.• CFCs a were once widely used in aerosol propellants, refrigerants, foams, and industrial processes.
• Other chemicals that damage the ozone layer include; I. methyl bromide (used as a pesticide), II. halons (used in fire extinguishers), III. methyl chloroform (used as a solvent in industrial processes for essential applications).• Methyl bromide and halons are broken apart, they release bromine atoms.• which are 60 times more destructive to ozone molecules than chlorine atoms.
• 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.
• When the ozone layer are thinned larger quantities of harmful ultraviolet rays to reach the earth.
• UV radiation includes: – UV-A, the least dangerous form of UV radiation, with a wavelength range between 315nm to 400nm. – UV-B with a wavelength range between 280nm to 315nm. – UV-C which is the most dangerous between 100nm to 280nm. UV-C is unable to reach Earth‘s surface due to nm stratospheric ozone‘s ability to absorb it. =“Nanometer”
Ozone depletion causes increases in UV rays‘s effects on aquatic ecosystems by: i. decreasing the abundance of phytoplankton – affects the food stock for fishes and the absorption of CO2. ii. decreasing the diversity of aquatic organisms – reduces food stock and also destroys several fish and amphibians.
i. Damage to plant cell DNA molecules - makes plants more susceptible to pathogens and pestsii. Reductions in photosynthetic capacity in the plant - results in slower growth and smaller leaves.iii. Causes mutations in mammalian cells and destroys membranes.
DNA absorbs UV-B radiation• Changes shape in DNA – Changes in the DNA molecule mean that enzymes cannot ―read‖ the DNA code . – Results in mutated cells or the cells die. Cells have developed the ability to repair DNA • A special enzyme arrives at the damage site. • removes the damaged section of DNA . • replaces it with the proper components.
i. Skin cancer.ii. eye disorders (blindness).iii. Immune system damage.iv. Premature aging (photoaging) of the skin (different from normal chronological aging). ! Possibly other things too that we dont know about at the moment.
• Because our atmosphere is one connected system, it is not surprising that ozone depletion and global warming are related in other ways.• The ozone hole, is not the mechanism of global warming. Ultraviolet radiation represents less than one percent of the energy from the sun—not enough to be the cause of the excess heat from human activities. – Global warming is caused primarily from putting too much carbon into the atmosphere when coal, gas, and oil are burned to generate electricity or to run our cars.
Will the ozone layer recover? Can we make more ozone to fill in the hole? – Provided that we stop producing ozone-depleting substances, ozone will be created through natural processes that should return the ozone layer to normal levels by about 2050.