Ozone Hole

Understanding Ozone http://royal. okanagan. bc 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 (O2) in the stratosphere UV radiation splits the ozone back to O and O2 and it can form another ozone molecule

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The Ozone Hole First discovered in 1985: observations from Antarctica extend back into 1950’s. 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 (CFC’s) Ozone hole not present in early 1970’s Observations over Antarctica data back to the 1950’s. The discovery of the ozone hole occurred in 1985. It turns out that the research group measuring ozone had seen a sharp decline in ozone levels during October over Antarctica (see next overhead), but didn’t report it immediately because they worried that their instrument might be faulty. Finally, after a few years of testing, they published a paper documenting this rapid decline of ozone levels. However, at the time, there was no explanation for why ozone was declining. During that same time period, NASA was also observing ozone levels globally. However, they didn’t expect to see signs of ozone depletion over Antarctica, and consequently, ‘missed’ the ozone hole due to a computer glitch. When they realized their mistake, and fixed up the computer problem, they also saw the clear signs of an emerging hole in the ozone layer. The ozone hole is characterized by a rapid depletion of ozone over Antarctica during the springtime. The science of the ozone hole was well understood by the early 1990s.

(Key Learning Figure) Many students (and the public) have the perception that the ozone hole (and ozone in general) is getting much worse. This is likely due to press reports that usually say, ‘the ozone hole reached it’s largest size…’ The reality is that in the last decade, the size and severity of the ozone hole have stayed about the same, compared to rapid changes seen in the middle 1980’s. Year to year variations in the depth and severity of the ozone hole is really a function of the atmospheric weather conditions (I.e. the colder the winter, the more greater the ozone loss). In addition, the ozone hole is about as bad as it can get. Between 16-22 km, all the ozone is essentially destroyed during spring over Antarctica, so it couldn’t get much worse. Thus, we don’t expect the size and depth of the ozone hole to change dramatically in the future. Rather, it is expected that the size of the ozone hole is about as big as it’s going to get, and with time (10 or more years) and reduced chlorine levels, we should start to see the size of the ozone hole get smaller. Thus, this graphic is intended to illustrate how in the 80’s, the size of the ozone hole increased rapidly, while in the 90’s and 2000, things stabilized.

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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. http://www.cnn.com/2001/TECH/space/10/17/ozone.hole.size/index.html

History of Ozone Depletion CFCs developed in 40’s and 50’s Refrigerants, propellants, fire retardants 1970’s CFCs detected in atmosphere. Many of these have long atmospheric lifetimes (10’s to 100’s of years) 1974 Rowland and Molina propose that CFC’s can destroy ozone in the stratosphere. CFCs broken apart by UV radiation forming chlorine which can destroy ozone quickly: O3 +Cl  ClO+ O2 (Catalytic Reaction) ClO+O  Cl+O2 (advanced) CFC’s are a class of chemicals that were developed in the 40 and 50s for many valuable applications including refrigerants, propellants (for spray cans) and fire retardants. One of the most remarkable and extremely valuable characterizes of CFC’s is that they do not react anything. Therefore, if you have some type of fire, you can safely use CFC’s to extinguish the fire, not worrying if your fire retardant is going to enhance the fire. This characteristics of CFC’s also means that many CFC’s remain in the atmosphere for many years (10’s to 100’s). They have long atmospheric lifetimes. Therefore, if you release a CFC molecule into the atmosphere, it may bounce around in the atmosphere for many many years. In 1974, two scientist (Rowland and Molina; who later received the Nobel Prize in chemistry) suggested that because CFC’s are around for a long time, they may eventually reach the upper atmosphere, where they can be broken apart by the sun. CFC’s contain chlorine, a chemical that can rapidly destroy ozone under certain conditions, and in some cases, a single chlorine atom may destroy thousands of ozone molecules through a self replicating cycles (catalytic reaction). The catalytic cycle is self replicating…ozone gets converted by chlorine, producing ClO and more oxygen. The ClO then reacts with a free oxygen atom, thereby producing another Cl atom. The cycle can then continue again.

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 + O3 »»» ClO + O2 ClO + O »»» Cl + O2

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breaking off a chlorine atom and leaving CFCl2. Sun Cl Cl Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. C Cl F UV radiation Cl Cl O O A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2. The chlorine atom attacks an ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2). Cl Cl O O O O O The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO) Cl O O O

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A single chlorine atom removes about 100,000 ozone molecules before it is taken out of operation by other substances

Low and Middle Latitudes 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

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

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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.

Natural Capital Degradation Effects of Ozone Depletion 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. 1995 (Vienna) 1997 (Montreal) 1999 (Beijing)

Ozone Depleting Chemicals Chlorofluorocarbons (CFCs) Halons Methyl bromide Carbon tetrachloride Methyl chloroform Hydrogen chloride

Former Uses of CFCs 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. 21-25 p. 489