Prepared by:

University of Sulaimani

Biology Dept.

School of

Sciences

¶ Shvan luqman.

Practical ecologyO zone Layer

Depletion3

The Earth’s Atmosphere

• 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.– Layers of the Earth's Atmosphere;

The atmosphere is divided into;I. Troposphere.II. Stratosphere.III.Mesosphere.IV. Thermosphere.

• The first layer above the surface and contains half of the Earth's atmosphere.

•Many jet aircrafts fly in it, because it is very stable. Also, the ozone layer absorbs harmful rays from the Sun.

•Meteors or rock fragments burn up in it.

•A layer is also where the space shuttle orbits.

•This is the upper limit of our atmosphere.

ozone• Ozone is a colorless gas, it relatively

simple molecule, consisting of three oxygen atoms bound together.

• Ozone is a highly-reactive from of oxygen, Near the Earth’s surface, hurt plant life, and damage people’s lung tissues.

• Ozone is a gas that occurs naturally in our atmosphere. Most of it is concentrated in the ozone layer, a region located in the stratosphere several miles above the surface of the Earth.

• Ozone also plays a vital role by shielding humans and other life from harmful ultraviolet “ultraviolet B”, light from the Sun.

ozone layer• 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 planet's ozone is in the ozone layer.

• While stratospheric ozone, which protects us from the sun.

Formation of ozone layerwhen short-wavelength UV light from the sun hits a molecule of oxygen gas. The light has so much energy that it breaks the oxygen bond holding the atoms together, thus creating two oxygen atoms. Through this process, the oxygen essentially absorbs the short-wavelength UV light, but this still leaves a significant amount of UV light with longer wavelengths, which is where ozone comes in.

Ozone Depletion• Ozone Depletion; 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 found above the Arctic. Stratospheric clouds in the Arctic

History• 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.

Ozone Depletion• 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.

• Cfc's are just one class of chemical substance that depletes the ozone layer, but they are the most important one.

Principal steps in the depletion of stratospheric ozone:

I. emissions: halogen source gases are emitted at earth’s surface by human activities and natural processes.

II. accumulation: halogen source gases accumulate in the atmosphere and are globally distributed throughout the lower atmosphere by winds and other air motions.

III. transport: halogen source gases are transported to the stratosphere by air motions.

IV. conversion: most halogen gases are converted in the stratosphere to reactive halogen gases in chemical reactions involving ultraviolet radiation from the sun.

V. chemical reaction: reactive halogen gases cause chemical depletion of stratospheric ozone over the globe.

VI.removal: air containing reactive halogen gases returns to the troposphere where the gases are removed by moisture in clouds and rain.

Causes of Ozone Depletion

• The cause of ozone depletion is the increase in the level of free radicals such as hydroxyl radicals, nitric oxide radicals and atomic chlorine and bromine.

• The most important compound, which accounts for almost 80% of the total depletion of ozone in the stratosphere are chlorofluorocarbons (CFC).

refrigerants & propellants

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.

CFC• 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.

Causes of Ozone Depletion

• 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.

Ozone destruction by sun light;

• 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.

What happened!!

• 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 stratospheric ozone’s ability to absorb it.

UV radiation!!!

nm = “Nanometer”

Effects of UV rays on Aquatic Ecosystems

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.

Effects of UV rays on Terrestrial Ecosystems

i. Damage to plant cell DNA molecules - makes plants more susceptible to pathogens and pests

ii. Reductions in photosynthetic capacity in the plant - results in slower growth and smaller leaves.

iii. Causes mutations in mammalian cells and destroys membranes.

DNA & UV-B 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.

Harmful effects of UV rays on human;

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 don't

know about at the moment.

ozone depletion and global warming

• 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.

Recovering of ozone layer

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.

Referencehttp://www.weatherquestions.com/What_is_

the_ozone_layer.htmhttp://environment.nationalgeographic.com/environment/global-warming/ozone-depletion-overview/http://www.patrickbrown.org/http://www.teachmefinance.com/Scientific_Terms/Ozone_Depletion.html#ixzz1pIchieF0http://news.nationalgeographic.com/news/2010/01/100127-ozone-hole-global-warming/http://earthobservatory.nasa.gov/Features/UVB/printall.phphttp://www.windows2universe.org/earth/Atmosphere/troposphere.html