Ozone and CFCs Intro

What is Ozone? Ozone is an allotrope of oxygen. It’s formula is O3. It is naturally present in the atmosphere. It exists both in the troposphere (lower atmosphere) and the stratosphere.

Ozone in the Stratosphere 90% of ozone is in the stratosphere It absorbs ultraviolet radiation which can be harmful to life on earth. Stratospheric ozone absorbs 97-99% of the sun’s ultraviolet radiation. It is formed in the following way: O2 (g) 2O (g) O2 (g) + O (g)  O3 (g)

Ozone in the Troposphere Ozone is harmful in the troposphere. It is toxic, and harmful to health at low concentrations (0.1 ppm) It forms photochemical smog by reacting with exhaust gases from motor vehicles. NO2 (g) + sunlight  NO (g) + O (g) The oxygen radicals then react with O2, forming ozone. O2 (g) + O (g)  O3 (g)

Chlorofluorocarbons (CFCs) Synthetic chemicals Contain fluorine, chlorine and carbon (no hydrogen) Have a similar structure to alkanes, with hydrogen replaced by fluorine and chlorine. E.g. Dichlorodifluoromethane

Source: Encyclopedia of the Atmospheric Environment Uses of CFCs Uses of CFCs Prior to the 1987 Montreal Protocol Source: Encyclopedia of the Atmospheric Environment http://www.doc.mmu.ac.uk/aric/eae/index.html

CFCs and Ozone 1 CFCs are chemically inert and are not broken down at low altitudes. They are also insoluble in water so they are not washed from the atmosphere in rain. They remain in the troposphere for long periods of time, and diffuse into the stratosphere. CFCs in the stratosphere cause damage to the protective ozone layer.

CFCs and Ozone 2 CFCs are broken down by UV radiation in the stratosphere releasing halogen atoms, such as chlorine, which can react to break up ozone molecules. CCl3F (g) + UV radiation  CCl2F (g) + Cl (g) Cl (g) + O3  ClO (g) + O2 (g) ClO then reacts with oxygen radicals ClO (g) + O (g)  O2 (g) + Cl (g) Since the chlorine atom is not used up in the reaction it can continue breaking up ozone molecules indefinitely. This removes ozone from the stratosphere, meaning it cannot perform it’s purpose of absorbing harmful UV rays as effectively.

Source: Environmental Protection Agency, USA Ozone Depletion Source: Environmental Protection Agency, USA

The Hole in the Ozone Layer

Effects of Ozone Depletion Global Warming Increase in levels of skin cancer, cataracts, immune system impairment. Impact on crops and agriculture Impact on marine food cycle

CFC Alternatives Impact of Chlorofluorocarbon Replacements on Stratospheric Ozone Source: http://www.mp-docker.demon.co.uk/environmental_chemistry/topic_2b/page_4.html

CFCs, HCFCs and HFCs