Presentation on theme: "Ozone Depletion Group 4. How Do We Know? Satellite Data From 1979 to 1995, ozone concentration declined by 6% in the latitudes 60 degrees north to 60."— Presentation transcript:
How Do We Know? Satellite Data From 1979 to 1995, ozone concentration declined by 6% in the latitudes 60 degrees north to 60 degrees south Over the South Pole, the decline was even greater- from 1956 to 1992, data shows a 50% decrease The destruction of ozone over the South Pole covers an area almost equal to the North American Continent
Satellite Data Continued In the Spring of 1996, the ozone levels in the Arctic were 45% below normal, and the Antarctic showed a 70% decrease in ozone levels
Background Information Ozone- O 3 Ozone is a naturally occurring bluish gas with highly reactive properties. It can have a harmful effect on living things. Inhalation of a small amount can be fatal Ozone is essential in the ozone layer, but it can have a harmful effect on living things. Inhalation of a small amount can be fatal The ozone layer is located about 15 to 45 kilometers above the earth and absorbs 99% of the suns harmful rays
Photo-Dissociation Ultraviolet light splits O 2 molecules into atoms. The atoms are extremely reactive free radicals. O 2 + uv light 2 O The free radicals react with oxygen molecules to produce ozone O 2 (g) + O (g) O 3 (g) The reverse reaction can also take place when ozone absorbs uv light. Ozone is constantly being formed and broken down.
How Ozone is Being Reduced Chlorofluorocarbons (CFCs) or freons Used as a propellant in spray cans, in old refrigerators and air conditioners, in fire extinguishers and as a solvent When CFCs reach unfiltered uv rays, the weakest bond, the C- Cl bond, breaks and creates a very reactive chlorine atom. They catalyze the reaction that converts ozone to diatomic ozygen CCl 2 F 2 + uv light CClF 2 + Cl The chlorine free radical reacts with ozone Cl + O 2 ClO + O 2 The newly formed ClO free radical can react with O ClO + O O 2 + Cl
Nitric Oxide The high temperature reaction of N 2 and O 2 in supersonic aircraft engines produces NO NO reacts with ozone NO + O 3 NO 2 + O 2 Effects of Ozone Depletion Increases cases of skin cancer and sunburn Damages to animals and plants Genetic mutations Changes in the worlds climate Promotes photochemical reactions responsible for smog Ozone near the earths surface attacks crops
Alternatives to CFCs The use of propane and 2-methyl propane as refrigerant coolants Although their use would reduce ozone depletion, both hydrocarbons are flammable and are greenhouse gases Fluorocarbons are not toxic or flammable and are stable to uv reactions, although they are greenhouse gases Hydrochlorofluorocarbons are more stable than CFCs, but they are only a temporary solution since the C-Cl bond is still present Hydrofluorocarbons are the best alternative because there is no chlorine atom present
Diatomic oxygen and ozone are allotropes Oxygen gas has a double bond between the two oxygen atoms Ozone has resonance structures, with one double bond and one single bond An oxygen molecule requires greater energy and lower wavelength of light to dissociate (212 nm or less) An ozone molecule requires less energy and a higher wavelength to dissociate (330 nm or less) Both oxygen and ozone protect the earth from much of the uv light
Ozone in Polar Regions During the polar spring, satellite data indicates a lower level of ozone over Antarctica Frigid temperatures in the winter trap very cold air at the pole and converts any water vapor to ice crystals Ice particles provide the surface area on which pollutants combine to produce reactive chemicals When the sun comes out in the spring, the uv light creates chlorine free radicals which create the hole in the ozone layer After the early spring, the ice crystals melt and can no longer provide the surface for the production of chlorine molecules Similar trends are found in the North Pole, but the temperatures are not as extreme as in the South Pole.