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Modern Chemistry II Department of Chemistry, Carnegie Mellon University Introduction to Kinetics: The Phasing Out of CFC’s

1930: Chapman’s theory of stratospheric ozone: 

1930: Chapman’s theory of stratospheric ozone Formation of ozone O2 + hv  O + O O + O2  O3 Ozone protects earth from UV rays O3 + hv  O2 + O O + O2  O3 Destruction of ozone O + O3  O2 + O2

1940’s and 1950’s: 

1940’s and 1950’s 1945: Most home refrigerators use CFC-12 as a safe refrigerant (CFC-12 = dichlorodifluoromethane, CF2Cl2) 1950: CFCs are used increasingly in manufacture of styrofoam.


1972 F. Sherwood Rowland attends talk in Ft. Lauderdale, Florida on discovery of new molecule in the atmosphere: CFC-12, CF2Cl2 Most scientists conclude this is nothing to worry about


1972 Molina Rowland Mario J. Molina leaves Mexico to attend graduate school at Berkeley, to study with Rowland Rowland and Molina begin thinking about implications of finding CFC’s in upper atmosphere


1973 Rowland and Molina: What will happen to CFC’s in the stratosphere? CCl3F +UV light → Cl +CCl2F (lasts 50 yrs) CCl2F2 + UV light → Cl + CClF2 (lasts 100 years) Proposed mechanism for chlorine atoms destroying ozone Cl + O3 → ClO + O2 ClO + O → Cl + O2 O3 + O → O2 + O2 (overall reaction)


1974 Molina and Roland publish paper in Nature entitled “The stratospheric sink for chlorofluoromethanes: chlorine atom-catalyzed destruction of ozone.” Receives little attention at first Rowland: “At the time, the figure we had was 6 billion spray cans produced every year in the world, and in our home we had 15 of them. So my wife went around and threw them all out, and I thought ’15 down, 6 billion to go.’”


1975 Molina: “We were talking about this invisible gas rising in the atmosphere to affect an invisible layer that was protecting us from invisible rays.” Molina: “The idea that a lot of people pressing these little buttons inadvertently were actually polluting the planet --- this eventually caught the attention of the press.” Value of CFCs produced: 2 billion dollars. Value of industrial processes that used them: 200 billion dollars.

Molina: looking back at 1975: 

Molina: looking back at 1975 “Isn’t it a responsibility of scientists, if you believe that you have found something that can affect the environment, isn’t it your responsibility to actually do something about it, enough so that action actually takes place? There was nobody else at that time that would actually fulfill that role. So that’s why Sherry and I, pretty consciously then, decided to take that additional step to make sure the government would actually pay attention.”


1976-1977 The use of CFCs in spray cans is banned first in the U.S., then in Canada, Norway, and Sweden. No other countries follow suit. CFCs continue to be used as refrigerants and solvents.

Early 1980’s: 

Early 1980’s Gradual improvement in techniques used to measure concentrations of chemical species in the stratosphere


1985 In early 80’s, the British Antarctic Survey notices a drop in ozone when the sun rises in the spring (September). At first, they thought this was a problem with their instruments. Publish their results in 1985.


1985 NASA TOMS (Total Ozone Mapping Spectrometer) realizes that the anomalously low values of ozone their software had been throwing away were real.


1986 Senator John Chafee of Rhode Island: “There is a very real possibility that man, through ignorance or indifference or both, has irreversibly altered the ability of our atmosphere to support life.” Representatives of fluorocarbon manufacturers emphasize that ozone depletion may be a completely natural phenomenon. Secretary of Interior Hodel: “perhaps it is possible to protect ourselves with sunglasses” (press responds by running cartoons of elephants, lions and zebras wearing sunglasses).


1987 Plan flights over the Antarctic just before October sun rise U2 spy plane to fly 3000 miles over the Antarctic and back again. One engine, with no backup plan for engine failure. Data collection is automatic, with no monitoring. Goal: simultaneous measurement of O3 and ClO: The “smoking gun” experiment


1987 Ozone detector worked fine ClO detector failed on first two flights (mid August) sketches in January unassembled hardware in May a marginally operational flight system in July software development—by an undergraduate--under the wing of the airplane in driving rain at stops in Panama and Chile Third flight (August 23): ClO high, Ozone normal Fourth flight (September 16): ClO high, 2/3 of ozone gone


1988 March 15: Press conference of Ozone Trends Panel concludes that ozone hole is caused by CFC’s “We’ve found more than the smoking gun. We’ve found the corpse.” March 25: DuPont Company, largest manufacturer of CFCs, announced that they would no longer manufacture these compounds.


1992 In Copenhagen, international agreement for a complete ban of production of CFCs by all industrialized countries by the end of 1995. Because of long recovery times, ozone hole over Antarctica will not disappear until around 2050.


Kinetics How do we think about the rate of reactions, such as those that destroy ozone? What is a mechanism? How do we support (prove) a mechanism?


Sources  Molina and Roland’s speech in honor of Senator Chafee http://www.ncseonline.org/NCSEconference/2000conference/Chafee Ozone Milestones http://remus.jpl.nasa.gov/milestones.htm Center for Atmospheric Science, University of Cambridge http://www.atm.ch.cam.ac.uk/tour/index.html

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