Dr. Matthew Lukeman Department of Chemistry Ozone Depletion Dr. Matthew Lukeman Department of Chemistry

Structure of the Atmosphere

Ozone is found throughout the stratosphere and troposphere, and the ‘ozone layer’ is where the concentration peaks. Where is Ozone Found?

Where is Ozone Found? Ozone concentrations vary with latitude.

How is Ozone Formed? Ozone is formed when atmospheric oxygen absorbs UV light (less than 240 nm). After it has absorbed light, oxygen (O2) will split into two oxygen atoms: O2 + light  2 O Each of these O atoms can react with other O2 molecules to make ozone (O3). O + O2  O3 + heat This is Chapman’s Theory

Ozone Formation

Where is Ozone Found? Ozone concentrations vary with latitude.

Ozone Formation

What does Ozone do? Ozone will absorb light below 320 nm, causing its dissociation: O3 + light  O2 + O These products can recombine to make ozone (O3) and give off heat. O + O2  O3 + heat The ozone layer serves to filter out the most harmful of the UV radiation coming from the sun.

Why do we care about UV levels? Health Effects on People – Skin Cancer vs Vitamin D production

Why do we care about UV levels? Effects on Crops - Some organisms are sensitive to UV levels. For example, cyanobacteria help fix nitrogen in important crops such as rice.

What is happening to our Ozone Layer?

What is happening to our Ozone Layer? A slow and steady decline has been observed in ozone levels over the past 30 years, approximately a 4% loss per decade.

Beware of Misleading Data

Statistical Treatment

What is Going On? 1970 - Paul Crutzen discovered that Nitrogen oxides can destroy atmospheric ozone catalytically. Remember that ozone absorbs light: O3 + light  O2 + O The following reactions also take place: NO +O3  NO2 + O2 NO2 + O  NO + O2 Net Reaction: 2 O3  3 O2

The Concorde

What is Going On? 1974 - Mario Molina and Sherwood Rowland show that man-made CFCs present throughout the atmosphere are bringing about the destruction of the ozone layer. CFCs are ChloroFluoroCarbons, widely used gases composed of chlorine, fluorine, and carbon containing compounds.

CFC Use

How do CFCs Affect O3? CFCs react with light and lose a chlorine atom: CFCl3 + light  CFCl2 + Cl Cl will destroy ozone catalytically as well: Cl +O3  O2 + ClO ClO + O  Cl + O2

What was done? Late 70s – US, Canada, and a few others try to reduce CFC use by limiting their use in aerosol cans. Strong opposition from industry, weak political will.

The Panic 1985 - The loss is far more drastic near the south pole than predicted. This phenomenon is dubbed the ‘ozone hole’.

The Hole

What was done? 1987 – Signing of the Montreal Protocol. 43 countries met and agreed to restrict output of CFCs to 1986 levels and reduce to 50% by 1999. Industry was onboard… why?? “...the chemical industry supported the Montreal Protocol in 1987 because it set up a worldwide schedule for phasing out CFCs, which [were] no longer protected by patents. This provided companies with an equal opportunity to market new, more profitable compounds." Dr. Mostafa Tolba, former head of the UN Environment Programme, June 30, 1990 1990 – Agreement was strengthened at meeting in London. They now agreed to nearly 100% phase out by 2000.

What was done? 1992 – Timeline was accelerated. 100% reduction aimed for 1996.

Is it working? CFC concentrations in the environment are beginning to level off.

The Future

The Future

Questions ?