Ozone

Same Molecule, Different Locations

TROPOSPHERIC OZONE -- “Bad”

A pale blue gas with a pungent odor that will irritate your eyes, nose and throat, damages lung tissue, and is toxic to organisms.

Used as a bleaching agent and sterilizing agent.

A major component of photochemical smog.

A potent greenhouse gas.

STRATOSPHERIC OZONE -- “Good”

Absorbs damaging solar UV radiation which is mutagenic and carcinogenic.

Protects life on earth.

Depletion of ozone is not the cause of global warming.

The ozone hole is the region over Antarctica with total ozone of 220 Dobson Units or lower.

The Stratospheric Ozone Layer

Ozone is measured in

Dobson Units

0.01 mm of ozone at STP is called a Dobson Unit (DU).

Named after Gordon M.B. Dobson, who designed the standard instrument used to measure ozone from the ground and developed the worldwide Dobson network, the only source of long-term data going back to 1956-57.

If the ozone layer over the US were compressed to STP it would be about 3 mm thick or 300 Dobson Units (DU).

Gordon M.B. Dobson (1889-1976)

1930 Pure Oxygen Chemistry

Production:

O2 + h —> O + O ( < .242 mm)

O + O2 + M —> O3 + M

Destruction:

O3 + h —> O + O2 ( < .320 mm)

O + O3 —> 2 O2

Sidney Chapman developed a theory of stratospheric ozone production based upon an equilibrium model consisting of the photochemical dissociation and recombination of oxygen.

1928 Invention of CFCs

Thomas Midgley, Jr. (1889-1944) an industrial chemist, developed Freon, a nonflammable, nontoxic compound (CFC-12) to replace the hazardous compounds then used as refrigerants. He inhaled the gas to demonstrate its safety.

Midgley also invented leaded gasoline!

CFC Lifestyle Issues

Hailed as chemically “inert” wonder chemicals

Air conditioning

Refrigerants

Aerosol sprays

hair spray, deodorants, paints

Styrofoam insulation

Furniture and carpet padding

Computers

Fire extinguishers (Halons)

Dry cleaning

Nitrogen-, Chlorine-, and Bromine-Ozone Chemistry

In 1962 Harry Wexler warned about Cl and Br catalytic reactions that could destroy Ozone.

In 1970, while examining the potential impact of supersonic transports (SSTs) on the stratosphere, atmospheric chemist Paul Crutzen identified an ozone-destroying catalytic cycle involving oxides of nitrogen.

In 1974 Mario Molina and F. Sherwood Rowland linked this cycle to the chlorine in CFCs.

Ozone destroyed by Chlorine

1. CF2Cl2 + UV -----> CF2Cl + Cl

Solar ultraviolet radiation interacts with a CFC molecule and breaks off a chlorine atom.

2. Cl + O3 -----> ClO + O2

The chlorine combines with an ozone molecule, destroys it, and forms chlorine monoxide and molecular oxygen.

3. ClO + O -----> Cl + O2

The chlorine monoxide combines with an atomic oxygen atom, releasing chlorine at the end of the process which can then destroy another ozone molecule as in step 2.

Net result: 100,000 O3 destroyed by one Cl

And the cycle repeats, destroying up to 100,000 ozone molecules

Effects of UV on Health & Environment

Sunburn and aging of the skinNon-melanomic skin cancerMalignant melanoma - fatalEye damage including cataracts & tumorsImmunosuppressionReduced crop yields and increased susceptibility to

pests and diseasesReduction in the growth of phytoplanktonDecrease in the numbers of aquatic speciesPossible mutations and genetic damage

1979 CFC Aerosol

Ban

The U.S., Canada, Norway, and Sweden banned the use of CFCs as aerosol propellants in response to projections of a 5 percent depletion of the ozone layer within 100 years. Annual production of CFCs, which had peaked at 2 billion lbs/yr decreased slightly and then leveled off for several years.

CFC Usage Grows in the 1980s and 1990s Growth of the sunbelt (air-conditioning), Computer industryWorldwide industrial developmentCFC use grew to over 2.5 billion lbs /yr

Antarctic "Ozone Hole" Discovered in 1985British Antarctic Survey reported a systematic reduction of 40

percent in the springtime (October) ozone measurements over Halley Bay.

330 DU in 1956 to 180 DU in 1985.Cl• and Br• reactions were implicated. U.S. Secretary of the Interior James Watt advises wearing hats,

sunscreen, and dark glasses.

BAS image 1985 NASA TOMS image 1987

1987 Montreal Protocol

Vienna Convention began the process in 1985.The Montreal Protocol on Substances that Deplete the Ozone Layer

was agreed on 16 September 1987 and entered into force on 1 January 1989. It is the primary international agreement providing for controls on the production and consumption of ozone-depleting substances such as CFCs, halons, and methyl bromide. As of 30 June 1994, 136 states had become Parties to the Protocol, including virtually all major industrialized countries and most developing countries.

CFC annual production was frozen at 1990 levels with 50 percent reduction by 2000. Annual production of halons to be frozen at 1993 levels.

Subsequent meetings of the parties are held regularly to monitor and accelerate the process including the London Amendment (1990), the Copenhagen Amendment (1992), the Montreal Amendment (1997) and the Beijing Amendment (1999).

Three scenarios

on stratospheric Chlorine

Meteorology of Ozone Depletion

The polar winter leads to the formation of the polar vortex which isolates the air within it.

Cold temperatures (less than 190 K) form inside the vortex; cold enough for the formation of Polar Stratospheric Clouds (PSCs) composed of ice and nitric acid.

PSCs provide a reaction surface for the ozone destruction reactions involving chlorine and bromine.

Many of the chemical reactions require sunlight, so the ozone destruction does not begin until the polar night ends in the late winter or early spring.

Ozone loss is rapid, especially over Antarctica in October.

The northern hemisphere is warmer than the southern hemisphere, it warms up earlier in the spring, and by the time there is sunlight available, the PSCs have already disappeared. This appears to explain why there is no Arctic ozone hole (yet). The Arctic stratosphere is significantly chemically perturbed, however.

Phaseout of Ozone-depleting chemicals

Hopeful projected recovery of ozone layer

http://nnvl.noaa.gov/Media/Ozone/MontrealProtocolGraph_compressed.mov

Thickness of the ozone layer (minimum value) over Halley Bay, Antarctica. Note the drastic depletion since 1980.

If there were no Montreal Protocol. . .

By 2050:

Ozone depletion would have been 50-70 percent in mid-latitudes.

UV-B would have doubled in Northern Hemisphere and quadrupled in Southern Hemisphere.

Five times more CFCs in the atmosphere with increased future damage.

130 million more eye cataracts.

19 million more non-melanomic skin cancers.

1.5 million more malignant melanomas - fatal.

What else can be done?

Full international compliance with the Montreal Protocol and its amendments.

Suppress black market CFCs

Total elimination of methyl bromide by 2004.

Total elimination of HCFCs by 2030.

Ensuring that CFCs and halons presently contained in existing equipment are never released to the atmosphere.

Wearing hats, sunglasses, and protective clothing while out of doors is prudent and highly advisable.

Ironically, sunblock may aggravate skin cancer! Provides false sense of security, leads to more time in the sun, greater exposure, prevents damaged skin from peeling.

1995 Nobel Prize in Chemistry

Won the Nobel Prize for Chemistry in 1995 for work on reactions involving the depletion of stratospheric ozone.

Paul Crutzen Mario Molina F. Sherwood Rowland

Web Resources

The Ozone Holehttp://www.theozonehole.com/basbulletins.htm Ozone Depletion FAQs http://www.faqs.org/faqs/ozone-depletion/

UNEP Ozone Secretariat

http://ozone.unep.org/