The reduction of ozone over Antarcticaover time. Area in purpleindicates the “ozone hole.”

Stratospheric Ozone Depletion

Ozone in the Stratosphere- What causes an Ozone hole?

FIGURE 01b: Ozone concentrations in the atmosphere and stratosphere

CFC

Three key ingredients in Polar Ozone Loss1. CFCs as source of catalyst, CFCs Cl radicals2. Sunlight3. Surface for heterogeneous reactions

How does ozone form in the stratosphere / what controls the concentration

Ozone is produced when an oxygen molecule and an oxygen atom combine:

O2 + O + M O3 + M

The source of the oxygen atom in the stratosphere is photolysis of O2:

O2 + hn O + O

So the basic series of reactions involving ozone in the are:

1. O2 + hn O + O2. O2 + O + M O3 + M3. O3 + hn O2 + O4. O3 + O O2 + O2

Possible Explanation for Major Ozone Loss- Refrigerants, CFCs Cl radicalsA catalytic cycle involves chlorine

Cl + O3 ClO + O2

ClO + O Cl + O2

O3 + hn O2 + O2O3 + hn 3O2

Eventually, Cl is “tied up” in reservoir species that do not participate in reactions involving O3

Cl + CH4 HCl + CH3ClO + NO2 + M ClONO2 + M

Ground based Observations of Ozone Loss over Antarctica

This enhanced depletion is related to stratospheric clouds

Ice

ClONO2

HCl

HOClCl2

Banning of CFCs

• 1987 Montreal Protocol

• 1990 London Agreement

• 1992 Copenhagen Amendments

FIGURE 5: Predicted concentrations of ozone-depleting chemicals in the atmosphere under various scenarios

Great Scientific Success- Announced in August of 2006-The ozone hole is in recovery!

FIGURE 04b: Computer-generated

images of the changing size of the ozone

hole over Antarctica

Courtesy of NASA/JPL/Agency for Aerospace Programs (Netherlands)/Finnish Meteorological Institute

Susan Solomon, senior scientist with the

National Oceanic and Atmospheric

Administration

• Solomon expects a full recovery of the ozone hole by 2060. But, she cautions, a lot of work must be done to reach that goal. "I think that it is very important to make sure that we actually measure ozone not only not getting any worse, but actually starting to improve to make sure that the actions that we have taken internationally have been effective."

• CFCs are long-lived and remain in the atmosphere for 50 to 200 years. But with global phase-out efforts, Solomon expects to see signs of a reduction in the ozone hole within a decade. Her job, she says, is to measure that process.