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Bay Area Earth Science Institute (BAESI)
Ozone depletion: Misconceptions San Jose State University, January 24, 2004 Weather and Climate
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How is ozone produced? Ozone is produced and destroyed naturally
Production: It is formed when oxygen absorbs solar radiation Ozone reacts with various other chemicals, and thus is highly reactive (i.e.) Net : O3 +O 2O2 One Cl atom can destroy ~100,000 ozone molecules O2 +UV radiation O+O O+ O2 O3 O3 + Cl ClO + O2 ClO + O Cl + O2 Weather and Climate
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Ozone, the good and the bad
Ozone is often confused: Good ozone: Stratospheric ozone The ozone layer Bad ozone: Tropospheric ozone Smog Stratosphere Altitude (km) Troposphere ozone amount
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UV radiation What affects the amount of UV radiation hitting the Earth? _______________________ UV radiation is absorbed by ozone, and scattered by clouds. Thus, determining the amount of UV radiation at the surface depends on your latitude, the time of day, the time of year, and how many clouds are above. Weather and Climate
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UV radiation Location (latitude) Time of year Time of day Cloud amount
What affects the amount of UV radiation hitting the Earth? _______________________ Location (latitude) Time of year Time of day Cloud amount UV radiation is absorbed by ozone, and scattered by clouds. Thus, determining the amount of UV radiation at the surface depends on your latitude, the time of day, the time of year, and how many clouds are above. Ozone amount Weather and Climate
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Concept Map Weather and Climate
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Concept Map Terms Ozone UV radiation Sun Gas Skin Cancer Summer Winter
Spring Atmosphere CFC’s South Pole Trends Ozone hole Chlorine Dobson Unit Total Ozone Tropospheric ozone Good ozone Stratospheric ozone Bad ozone Weather and Climate
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History of Ozone Depletion
Chlorofluorocarbons (CFCs) developed in 1940’s and 50’s as: 1970’s CFCs detected in upper atmosphere. Many of these have long atmospheric lifetimes: 1974 Rowland and Molina propose that CFC’s can destroy ozone in the stratosphere. CFC contain chlorine (Cl) Refrigerants, propellants, fire retardants (10’s to 100’s of years) Chlorine can destroy ozone rapidly Weather and Climate
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What causes the ozone hole?
Ozone Hole Recipe (make your own!) 1. _____________________ 2. _____________________ Formation of Polar Stratospheric Clouds (PSC’s) 3. ______________________ Winter Polar Vortex is region of strong winds forming an isolated ‘container’ from the middle latitudes. This produces cold temperatures. Allows chemistry to develop undisturbed. Weather and Climate
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What causes the ozone hole?
Ozone Hole Recipe (make your own!) 1. _____________________ 2. _____________________ Formation of Polar Stratospheric Clouds (PSC’s) 3. ______________________ Winter Polar Vortex is region of strong winds forming an isolated ‘container’ from the middle latitudes. This produces cold temperatures. Allows chemistry to develop undisturbed. Abundant chlorine Cold temperatures Sunlight to activate chemistry Weather and Climate
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Is the ozone hole getting much bigger?
Lesson 4: This is a graph showing the size of the ozone hole, measured as area where total ozone values are below 220 Dobson units, from the 1980’s through 2000. It is clear, that from the middle of the 1980’s, through to the middle of the 1990’s, the size of the ozone hole each year grew rapidly. However, since 1995, the size of the ozone hole has not grown much, rather stayed near about 25 million square kms. 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 often report, ‘the ozone hole reached it’s largest size…’ etc. 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 earlier years. Why has the ozone hole stayed nearly constant for the last 10 years? The short answer is that it’s about as bad as it can get. The size of the ozone hole is largely controlled by atmospheric weather conditions, such as how cold the winter is, and how variable winds are. Even if there was more chlorine in the atmosphere, that doesn’t necessarily change the temperature (this may be happening with global warming, but we’ll talk about that later). So, we don’t expect the size of the ozone hole to increase much more in the future. In fact, it is expected that because of chlorine controls by the Montreal Protocol, we should see the size of the ozone hole gradually begin to get smaller. However, this may take quite some time, maybe up to 50 years or more before the ozone hole disappears. Aim: The graphic serves to illustrate how in the 80’s, the size of the ozone hole increased rapidly, while in the 90’s and 2000, things stayed about the same. Discussion Questions: When was the ozone hole first observed? How do you define the size of the ozone hole? What year was the ozone hole the largest? What year was the ozone hole the smallest? When did the ozone hole grow the fastest? Has the ozone hole been growing fast recently? How do you expect ozone values to change over the next decade? Weather and Climate
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Is the ozone hole getting much bigger?
No, not over the last few years Lesson 4: This is a graph showing the size of the ozone hole, measured as area where total ozone values are below 220 Dobson units, from the 1980’s through 2000. It is clear, that from the middle of the 1980’s, through to the middle of the 1990’s, the size of the ozone hole each year grew rapidly. However, since 1995, the size of the ozone hole has not grown much, rather stayed near about 25 million square kms. 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 often report, ‘the ozone hole reached it’s largest size…’ etc. 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 earlier years. Why has the ozone hole stayed nearly constant for the last 10 years? The short answer is that it’s about as bad as it can get. The size of the ozone hole is largely controlled by atmospheric weather conditions, such as how cold the winter is, and how variable winds are. Even if there was more chlorine in the atmosphere, that doesn’t necessarily change the temperature (this may be happening with global warming, but we’ll talk about that later). So, we don’t expect the size of the ozone hole to increase much more in the future. In fact, it is expected that because of chlorine controls by the Montreal Protocol, we should see the size of the ozone hole gradually begin to get smaller. However, this may take quite some time, maybe up to 50 years or more before the ozone hole disappears. Aim: The graphic serves to illustrate how in the 80’s, the size of the ozone hole increased rapidly, while in the 90’s and 2000, things stayed about the same. Discussion Questions: When was the ozone hole first observed? How do you define the size of the ozone hole? What year was the ozone hole the largest? What year was the ozone hole the smallest? When did the ozone hole grow the fastest? Has the ozone hole been growing fast recently? How do you expect ozone values to change over the next decade? Weather and Climate
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What is being done about ozone depletion?
Montreal Protocol ~ (1988) international agreement to phase out ozone depleting chemicals Further amendments accelerated the phase out. Developed countries have switched to HCFC’s (more ozone friendly!) Developing countries have until 2004 to phase out CFC’s. Weather and Climate
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Is the Montreal Protocol working?
Seems to be… Recent observations indicate that chlorine is beginning to decline in the atmosphere. Weather and Climate
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Weather and Climate
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What is the connection between ozone depletion and global warming?
No direct connection between these environmental issues. Global warming produces: Tropospheric warming & stratospheric cooling Therefore, if the stratosphere cools, then ozone destroying chemistry (e.g. ozone hole), will increase. However: Global warming may enhance ozone depletion Weather and Climate
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What are predictions for the future?
Model simulations suggest: atmospheric chlorine will return to pre-80’s level __________________ . Uncertainties still remain: ____________________ In next 50 years or so A slow ozone recovery should follow decreasing chlorine concentrations!!! Phase out of CFC’s Influence of global warming Weather and Climate
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Concept Map Terms Ozone UV radiation Sun Gas Skin Cancer Summer Winter
Spring Atmosphere CFC’s South Pole Trends Ozone hole Chlorine Dobson Unit Total Ozone Tropospheric ozone Good ozone Stratospheric ozone Bad ozone Recovery TOMS Gas 2050 Cold temperatures Northern Hemisphere Weather and Climate
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Example of ozone concept map Example of ozone concept map
Troposphere Atmosphere Gas Ozone Hole Bad Ozone Good Ozone has UV Radiation Stratosphere Chlorine CFC’s cause is depletion of is a is present in the destroy produces present in produce protects the earth from contain Total Ozone Dobson Unit Global Warming Skin Cancer Sun Spring Automobiles may cause is the column causes is measurement of Ozone Troposphere Atmosphere Gas Ozone Hole Bad Ozone Good Ozone has UV Radiation Stratosphere Chlorine CFC’s cause is depletion of is a is present in the destroy produces present in produce protects the earth from contain Total Ozone Dobson Unit Global Warming Skin Cancer Sun Spring Automobiles may cause is the column causes is measurement of Example of ozone concept map Concept Map Terms Ozone UV radiation Sun Gas Skin Cancer Summer Winter Spring Atmosphere CFC’s South Pole Trends Ozone hole Chlorine Dobson Unit Total Ozone Tropospheric ozone Good ozone Stratospheric ozone Bad ozone TOMS Example of ozone concept map Concept Map Terms Ozone UV radiation Sun Gas Skin Cancer Summer Winter Spring Atmosphere CFC’s South Pole Trends Ozone hole Chlorine Dobson Unit Total Ozone Tropospheric ozone Good ozone Stratospheric ozone Bad ozone TOMS
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Misconceptions Ozone depletion and global warming often confused
Ozone depletion – CFC’s (aerosols, refrigerants) Global Warming – burning of fossil fuels Some student ideas Hole in ozone hole allows more heat into atmosphere Automobile exhaust responsible for ozone depletion … Weather and Climate
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