I. Introduction to Ozone

II. Introduction to CFCs

III. Why is Cl so Devestating to Ozone

IV. Mechanism of Ozone Decomposition

IV. Ozone Town Meeting

V. Scientific Basis of Good and Bad Ozone



I. Introduction to Ozone

Definitions

Ozone
O3
Ozone is a Resonance Structure

Ultraviolet Radiation
Radiation from 350 - to - 10 nm wavelength

Atmosphere layers
KM (kilometers) Differences in Composition

0-17 Troposphere
17-50 Stratosphere 1K < H2O and 1K > O3 than Trop.
50-90 Mesosphere
90-100 Ionosphere

Stratosphere
Contains Ozone layer with ~99% of Ozone
17-26 miles
Ozone layer 0.005 cm (0.1 in.) thick at 1 atm


II. Introduction to CFCs

CFC's - chlorofluorocarbons
Commercial name from DuPont - Freons
replaced sulfur dioxide (SO2) and ammonia (NH3) as refrigerants approximately 50 yrs. ago


CFC's
Chemical Name Formula Commercial Name
trichlorofluoromethane CCl3F CFC-11 (Freon-11)
dichlorodifluoromethane CCl2F2 CFC-12 (Freon-12)
chlorodifluoromethane CHClF2 CFC-22 (Freon-22)
1,1,2-trichloro-1,2,2-trifluoroethane Cl2FCCClF2 CFC-113 (Freon-113)

Naming of CFC's:

Units digit is # of F atoms
Tens digit is the # of H atoms plus1
Hundredths digit is the # of C atoms minus 1

Ex. CFC-113 has 1 C atom ( # - 1 ), 1 H atom ( # + 1), 3 F atoms ( = #)

CFC characteristics:

stable
odorless
non corrosive
nonflammable
non toxic
high heat of vaporization
optimum vapor pressure

Hypotheses of effect on Ozone presented

The possible depletion of Ozone by Anthropogenic gases was first proposed by H. S. Johnson of the U. of CA, Berkeley in the 1960s.

Effect on ozone of CFCs was theorized in 1974 by two chemists, Sherwood Rowland and Mario Molina from the University of California, Irvine.

Uses of CFCs

Other Sources of Halogenated Molecules in the Atmosphere as Gaseous

Bromine-containing compounds called halons for fire extinguishers

Carbon tetrachloride (extremely non-polar solvent)

1,1,1-trichloroethane solvent in products such as dry-cleaning and spray adhesives

Demographics

MDCs (industrialized countries) use 84% of CFCs

US is 25% of global consumption of CFCs

Vehicle air conditioners account for about 3/4 of US CFC emissions

By year 2000, 75 countries will phase out all CFC use.

Cumulative concentration of organochlorine in the atmosphere.



III. Why is Cl so Devastating to Ozone?

How long does a CFC last in the atmosphere

Over 50-400 years?

Freons without any hydrogen atoms have an average life time of 100 years in the atmosphere.

Time is needed to drift up in the atmosphere to reach the Stratosphere

One Cl atom can convert 10,000 to 100,000 O3 to O2 and O

Hydrogen containing CFCs only last a relatively short time and probably never make it to the Stratosphere. CH3CCl3 and CHClF2 only last 6-7 years.

What is the difference between Hydrogen containing CFCs?

Method of destruction in Troposphere

The hydroxyl radical is the natural air cleanser of the Troposphere.

This path is not available to fully saturated cloro and fluoro CFCs.


Formation of Ozone

Photodissociation Reaction

Step A

Step B

Step C

Back to Step B again
O3 200 - 360 nm


Other sources of O3 in the Troposphere

Electrical discharge:

Blue liquid with distinct odor



IV. Mechanism of Ozone Decomposition

CFC travels just above the O3 layer in the Stratosphere

Eq-1

It then drifts back into the lower Stratosphere where O3 is in high concentrations

Eq-2

Direct destruction of Ozone

Eq-3

Short circuit of Step a and c of Ozone UV protection cycle.

Life of Cl atom in atmosphere is 1-2 years.

In 1-2 years, one Cl atom will repeat Eq-2 100,000 times.
One Cl atom destroys ~10^(5) the number of O3 atoms.

Lasar radar system measurment of ozone concentration over Antarctica.

A map of ozone over Antarctica obtained from the Nimbus 7 satellite.

Simultaneous measurements of chlorine monoxide and ozone concentrations.

Seasonal thinning or loss of ozone.

Why is there an Ozone hole over Antarctic and
a similar effect over the Arctic?

Catalysis

Ice crystals absorb CFCs and provide a surface for Ozone molecule interaction (catalyst effect) in effect speeding up the reaction.


Hydroxyl radical Natural atmospheric cleansers (Troposphere)



"Ozone a Town Meeting" Oct. 1992

Video Notes

1985 - 25 nations banned CFCs
1988 - Output cut in half
1986 - Freeze on CFC production and 70 Countries
1990 - Phase out all CFC use by year 2000
(US to phase out all production by 1995)

Panelists

Peter Hackes - Journalist

Dr. Robert Watson - NASA
In charge of Ozone science at NASA

Eileen Claussen - EPA
Requiring recycling of CFCs

Ge'rard Me'gie - Physics Dept. U of Paris
President of International Ozone Commission
Ozone 100 yrs.

Dr. Helen Connon - DuPont
Fluorochemicals Dept.
50% today of level of 1986
Equipment using CFCs worth 135 billion
air-conditioning and refrigeration

Dr. Paul Crutzen - Max Planck Institute
90% of O3 in Stratosphere, 10% in Troposphere
O3 + UV purify atm. at Tropospheric level, cleans of other Industrial pollutants Loss of O3 is in Stratosphere
But if O3 increases in Troposphere it could be dangerous.
O3 is powerful greenhouse gas

Dr. John Sigmon -
House Science, Space, and Technology Committee
5% of population, 25% of Energy
Policy is made on imperfect data
Transfer of technology of environmental technology to other countries.

Notes on debate

UV Causes

Can O3 hole be fixed?

Life of CFC is long and we have damaged it to yr. 2100

15-18 yrs. no CFCs in spray cans in US

CFC agreements

Montreal Protocol 1987 - 50% reduction
2000 - 74-65 countries agree to phase out
1995 - all major countries have signed except India

Good O3 and bad O3
In Troposphere O3 can be bad, but it still consumes UV
O3 anywhere is UV shield

HFC 134A

600,000 Skin Cancers/yr. in USA

Requires Government Policy
International Policy
EPA
International Science

Refuting Scientific Arguments
Profit and patent
Cost to US in down economy
Monitoring UV daily dose
Ozone Graphics and References




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Revised 11/17/98