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The Ozone Layer
Transcript of The Ozone Layer
Christina Angelopoulos THE OZONE LAYER The History of Ozone The Chapman Cycle The Ozone Cycle and the Chemistry of Oxygen The Ozone's Functions The Ozone's Properties The Ozone's Functions The Ozone Depletion
O2 + light ---->2O (120 – 210 nm)
O + O2 ----> O3*
(a) O3*---->O3+M* (generates heat)
The overall effect is to convert penetrating UV light into heat, without any net loss of ozone.
The formation of ozone is responsible for absorption of high energy ultraviolet light
(b) O3 + light ----> O2 + O (220 – 320 nm)
Termination : O3 + O ----> 2 O2
Destruction of Ozone, Ozone Depletion
contains 3 O contains 2 O
is blue in color is colorless
has a strong odor. is odorless.
Ozone is much less common than normal oxygen.
Out of each 10 million air molecules, about 2 million are normal oxygen, but only 3 are ozone.
Occurs naturally in our atmosphere. - It absorbs a portion of the radiation from the sun, preventing it from reaching the planet's surface.
-It absorbs the portion of ultraviolet light called UVB.
UVB has been linked to many harmful effects, including various types of skin cancer, cataracts, and harm to some crops, certain materials, and some forms of marine life. About 2.5 billion years ago some prokaryotic cells (ex., cyanobacteria) acquired the ability to photosynthesize.
The energy of sunlight was captured, and oxygen was generated as a waste product.
Oxygen increased in concentration in the atmosphere, making aerobic metabolism possible.
O3(ozone) accumulation in the upper atmosphere In, 1930 Sydney Chapman proposed a series of reactions to account for all of the reactions in the ozone layer At any given time, ozone molecules are constantly formed and destroyed in the stratosphere.
The total amount, however, remains relatively stable. Although ozone represents only a small fraction of the gas present in the atmosphere, it plays a vital role by shielding humans and other life from harmful ultraviolet light from the Sun. Ultraviolet radiation and stratospheric ozone Effects of the ozone depletion when this ozone becomes depleted, more UV rays, particularly UV-B radiation will reach the earth.
•Exposure to higher amounts of UV radiation has serious negative impacts on:
3.Plants, agriculture, forestry and natural ecosystems
5.Human health Effects on materials •Increased UV-B degrades wood, plastic, paper, rubber, fabrics, cotton and wool Effects on marine life and aquatic ecosystems •UV-B penetrates water columns to depths of 30m
•Increased UV radiation threatens plankton
•Photosynthesis and growth of phytoplankton is severely inhibited by UV exposure
• Decrease in plankton disrupts the fresh and saltwater food chains
•Loss of biodiversity in oceans, rivers and lakes Effects on plants, forests and natural ecosystems •Several major crop species are vulnerable to increased UV-B
•Reduction of growth, photosynthesis and flowering for wheat, rice corn, peas, tomatoes, cucumbers, cauliflower, broccoli and carrots.
•Changes patterns of genes in plants Effects on animals and amphibians Eye and skin cancers for domestic animals
UV-B radiation is one of the main reasons for the decline of amphibians Effect on human health Weakens human immune system
Causes skin cancer such as basal cell, squameous cell, malignant melanoma(risk increase 20%) and non-malignant melanoma(risk increase 26%)
Premature aging of skin
Increase risks of eye cancer, pterygium and cataracts Measures taken to counter the effects of ozone depletion Vienna convention held in 1985
Montreal Protocol adopted in 1987
Enviornmental Protection Agency (EPA) enforced Montreal Protocol in U.S What we can do about the ozone layer depletion Avoid using air conditioner, refrigerators and freezers that contain may contain CFC's
Avoid using fire extinguisher that contains halons
Use sunscreen with high SPF
Use lipbaum with SPF
Use sunglasses with 100% UV block
Hats Ozone depletion recovery According to Environment Canada, ozone layer recovery expected by 2050
According to MetOp weather satellite, the hole over the South Pole in 2012 was the smallest it has been in the last 10 years
Ozone layer seems to be on a road to recovery over Antartica
Slow recovery Causes of the ozone depletion Meteorological factor:
•movement of air from one place to another in stratosphere
• Cold temperature in the upper atmosphere causes nitric acid to freeze into crystals that form a wispy pink clouds
•It forms a vortex of tight and twisted winds which leads to a formation of the ozone hole
manufactured chemicals that contain chlorine and bromine destroy ozone at faster rates
Ozone depleting substances:
Chlorofluorocarbons (CFC's) responsible for over 80% of total stratospheric ozone depletion
Hydrochlorofluorocarbons (HCFC's) •Ozone depletion is the thinning or destruction of the ozone layer in the stratosphere
•The "ozone hole" over Antarctica which is approximately the size of the USA where the ozone has become depleted
•It was discovered in 1985 by British Antartic survey scientists Farman, Gardiner and Shanklin
•total ozone values less than 220 dobson units, nothing lower than this value was ever observed prior to 1979
X• + O3 –––––––> XO• + O2
XO• + O –––––––> X• + O2
net : O3 + O –––––––> 2O2