Presentation on theme: "Ozone Hole. Understanding Ozone"— Presentation transcript:
Understanding Ozone Discovered in 1839 by German scientist Christian Friedrich Schonbein Pale blue, unstable molecule made of three oxygen atoms Vital to life in the stratosphere Harmful to plants and humans in the troposphere Concentration: stratosphere up to 15 ppm at about 25 km Formed when atomic oxygen (O) from higher parts of the atmosphere collides with molecular oxygen (O 2 ) in the stratosphere UV radiation splits the ozone back to O and O 2 and it can form another ozone molecule
The Ozone Hole First discovered in 1985: observations from Antarctica extend back into 1950s. Characterized as a rapid depletion of ozone over Antarctica during spring. Ozone hole season, Spring (August – October) Ozone hole located over mainly over Antarctica. Ozone hole recovers by late December Ozone hole caused by human chemicals (CFCs) Ozone hole not present in early 1970s
Ozone hole stabilizes October 17, 2001 WASHINGTON (CNN) -- A hole in the Earth's protective ozone layer is about the same size as in the past three years, according to scientists at the National Oceanic and Atmospheric Administration, who predict it will hold steady in the near future. Satellite data show the hole over Antarctica, which allows more harmful solar radiation to reach the Earth, peaked this year at about 10 million square miles (26 million square km), roughly the size of North America.
History of Ozone Depletion CFCs developed in 40s and 50s Refrigerants, propellants, fire retardants 1970s CFCs detected in atmosphere. Many of these have long atmospheric lifetimes (10s to 100s of years) 1974 Rowland and Molina propose that CFCs can destroy ozone in the stratosphere. CFCs broken apart by UV radiation forming chlorine which can destroy ozone quickly: O 3 +Cl ClO+ O 2 (Catalytic Reaction) ClO+O Cl+O 2
Chlorofluorocarbons or CFCs First produced by General Motors Corporation in 1928, CFCs were created as a replacement to the toxic refrigerant ammonia CFCs have also been used as a propellant in spray cans, cleaner for electronics, sterilant for hospital equipment, and to produce the bubbles in Styrofoam
CFCs are cheap to produce and very stable compounds, lasting up to 200 years in the atmosphere Many countries have recently passed laws banning nonessential use of these chemicals. Nevertheless, by 1988 some 320,000 metric tons of CFCs were used worldwide.
Action of CFCs CFCs created at the Earth's surface drift slowly upward to the stratosphere where UV radiation from the sun causes their decomposition and the release of chlorine Chlorine in turn attacks the molecules of ozone converting them into oxygen molecules Cl + O 3 »»» ClO + O 2 ClO + O »»» Cl + O 2
Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl 3, breaking off a chlorine atom and leaving CFCl 2. UV radiation Sun Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O 2. The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO) The chlorine atom attacks an ozone (O 3 ) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O 2 ). Cl C F O O O O O O O O O O
A single chlorine atom removes about 100,000 ozone molecules before it is taken out of operation by other substances
Current measurements indicate that the amount of ozone in the stratosphere of the low and middle latitudes has decreased by about 3% with estimates that it will decrease by10% by 2025 Low and Middle Latitudes
Harmful effects of UV radiation. Skin cancer (ultraviolet radiation can destroy acids in DNA) Cataracts and sun burning Suppression of immune systems Adverse impact on crops and animals Reduction in the growth of ocean phytoplankton Cooling of the Earth's stratosphere and possibly some surface climatic effect Degradation of paints and plastic material
Conclusion Ozone Depletion Exists and effects certain areas of the Earth more than others Currently, one in five North Americans and one in two Australians will develop some form of skin cancer in their lifetime With a sustained 10% decrease in stratospheric ozone, an additional 300,000 non-melanoma and 4,500 melanoma skin cancers could be expected world-wide, according to UNEP estimates.
Effects of Ozone Depletion Natural Capital Degradation Human Health Worse sunburn More eye cataracts More skin cancers Immune system suppression Food and Forests Reduced yields for some crops Reduced seafood supplies from reduced phytoplankton Decreased forest productivity for UV-sensitive tree species Wildlife Increased eye cataracts in some species Decreased population of aquatic species sensitive to UV radiation Reduced population of surface phytoplankton Disrupted aquatic food webs from reduced phytoplankton Air Pollution and Materials Increased acid deposition Increased photochemical smog Degradation of outdoor paints and plastics Global Warming Accelerated warming because of decreased ocean uptake of CO2 from atmosphere by phytoplankton and CFCs acting as greenhouse gases
Montreal Protocol An international treaty designed to protect the ozone layer phasing out production of number of substances believed to be responsible for ozone depletion Effective January 1, 1989 Five revisions 1990 (London) 1992 (Copenhagen) accelerated the phasing out of key ozone- depleting chemicals (Vienna) 1997 (Montreal) 1999 (Beijing)
Former Uses of CFCs Air Conditioners Refrigerators Spray cans Cleaners for electronic parts Sterilizing medical instruments Fumigants for granaries and cargo ships Air Conditioners Refrigerators Spray cans Cleaners for electronic parts Sterilizing medical instruments Fumigants for granaries and cargo ships
Solutions: Protecting the Ozone Layer CFC substitutes Montreal Protocol Copenhagen Protocol Fig p. 489