1. Ozone depletion E.4.2-4.3 Presentation by Dina Goodman

2. What is the ozone layer, anyway? A layer that occurs in stratosphere between 12 km and 50 km above the Earth’s surface. A layer that occurs in stratosphere between 12 km and 50 km above the Earth’s surface. The natural “steady state” of the ozone layer has been lost because of ozone-depleting pollutant. The natural “steady state” of the ozone layer has been lost because of ozone-depleting pollutant. About 4% of the ozone layer has been lost per decade since the 1970s. About 4% of the ozone layer has been lost per decade since the 1970s. The ozone layer prevents most harmful UVB wavelengths (270–315 nm) of UV light from passing into the Earth’s atmosphere. Thus several biological consequences as increases in skin cancer, cataracts, damage to plants, and reduction of plankton populations are attributed to ozone depletion. The ozone layer prevents most harmful UVB wavelengths (270–315 nm) of UV light from passing into the Earth’s atmosphere. Thus several biological consequences as increases in skin cancer, cataracts, damage to plants, and reduction of plankton populations are attributed to ozone depletion.

3. E.4.2- Ozone-Depleting Pollutants Chlorofluorocarbons (CFCs) Chlorofluorocarbons (CFCs) Contains: Cl, F, C Contains: Cl, F, C Sources: developed in 1930s for various of industrial, commercial, and household applications. CFC have desirable safety characteristics (non-toxic, non-flammable, and non- reactive) and stable thermodynamic properties, so they are ideal for many applications, e.g coolants for commercial and home refrigeration units, aerosol propellants, electronic cleaning solvents, and blowing agents. Sources: developed in 1930s for various of industrial, commercial, and household applications. CFC have desirable safety characteristics (non-toxic, non-flammable, and non- reactive) and stable thermodynamic properties, so they are ideal for many applications, e.g coolants for commercial and home refrigeration units, aerosol propellants, electronic cleaning solvents, and blowing agents. In 1973 discovered to be a catalytic agent in ozone destruction because the ultraviolet radiation breaks the weak C-Cl bond and form radicals. In 1973 discovered to be a catalytic agent in ozone destruction because the ultraviolet radiation breaks the weak C-Cl bond and form radicals.

4. E.4.2- Ozone-Depleting Pollutants cont. Oxides of nitrogen (NO x ) Oxides of nitrogen (NO x ) Nitric Oxide: produced during combustion. So in areas with a large amount of vehicle traffic, e.g. Atlanta, the amount of nitrogen oxides emitted into the atmosphere can be quite significant. Nitric Oxide: produced during combustion. So in areas with a large amount of vehicle traffic, e.g. Atlanta, the amount of nitrogen oxides emitted into the atmosphere can be quite significant. Nitrous oxide: laughing gas, propellant Nitrous oxide: laughing gas, propellant When exposed to sunlight, Oxides of nitrogen react and form photochemical smog. When exposed to sunlight, Oxides of nitrogen react and form photochemical smog.

5. E.4.3 Alternatives to CFCs Since the creation of the Montreal Protocol in 1987, fewer CFCs have been used. Since the creation of the Montreal Protocol in 1987, fewer CFCs have been used. Alternatives should have similar properties, such as low reactivity, low toxicity, and low flammability, but they do not contain the weak C-Cl bond. Furthermore they shouldn’t absorb infrared reaction, or else will be greenhouse gases. Alternatives should have similar properties, such as low reactivity, low toxicity, and low flammability, but they do not contain the weak C-Cl bond. Furthermore they shouldn’t absorb infrared reaction, or else will be greenhouse gases. Examples: - Hydrocholorofluorocarbons (HCFCs) e.g. CHF 2 Cl Examples: - Hydrocholorofluorocarbons (HCFCs) e.g. CHF 2 Cl - Hydrofluorocarbons (HFC) e.g. CF 3 CH 2 F - Hydrocarbons e.g. C 4 H 10