9-03-1 Formation of the Ozone Layer

9-03-1 Formation of the Ozone Layer - Formation of the...

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Formation of the Ozone Layer (OZONE O ) 1. Over two billion years ago, early aquatic organisms called blue-green algae began using energy from the Sun to convert molecules of water (H 2 O) and carbon dioxide (CO 2 ) and recombine them into organic compounds and molecular oxygen (O 2 ). This solar energy conversion process is known as photosynthesis. Some of the photosynthetically created oxygen began to accumulate in the atmosphere, touching off a massive ecological disaster with respect to early existing anaerobic organisms. As oxygen in the atmosphere increased, CO 2 decreased. 5M ' 2. High in the atmosphere, some oxygen (O 2 ) molecules absorbed energy from the Sun's ultraviolet (UV) rays and split to form single oxygen atoms. These atoms combined with molecular oxygen (O 2 ) to form ozone (O 3 ) molecules, which are very effective at absorbing UV rays. The thin layer of ozone that surrounds Earth acts as a shield, protecting the planet from irradiation by UV light. 5M ' O OZONE O The amount of ozone required to shield Earth from biologically lethal UV radiation, wavelengths from 200 to 300 nanometers (nm), is believed to have been in existence 600 million years ago. At this time, the oxygen level was approximately 10% of its present atmospheric concentration. Prior to this period, life was restricted to the ocean. The presence of ozone enabled organisms to develop and live on the land. Science of the Ozone Layer Image of the latest global distribution of ozone September 16th is the "International Day for Preservation of the Ozone Layer" as designated by the United Nations O OZONE O 1. Ozone is constantly being produced and destroyed in a natural cycle . However, the overall amount of ozone is essentially stable. This was the situation until the past several decades.
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2. Large increases in stratospheric chlorine and bromine have upset that balance. Ozone levels are beginning to fall towards a lower level until a new balance can be achieved. 3. The ozone depletion process (picture below) begins when CFC's and other ozone-depleting substances (ODS) leak or are released from equipment. Winds efficiently mix the troposphere and evenly distribute the gases. CFC's are extremely stable, and they do not dissolve in rain. After a period of a few years, ODS molecules reach the stratosphere. Strong UV light breaks apart the ODS molecule. CFC's release chlorine atoms and halons release bromine atoms. It is these atoms that actually destroy ozone, not the intact ODS molecule. It is estimated that one chlorine atom can destroy over 100,000 ozone molecules before finally being removed from the stratosphere. Chlorofluorocarbons (CFC's) 1. A class of compounds that have been used as refrigerants, aerosol propellants (for spray cans), foam blowing agents (for manufacture of styrofoam and insulation), and as solvents (for cleaning in the electronics industry). 2. They are chemically
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9-03-1 Formation of the Ozone Layer - Formation of the...

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