AIR ENVIRONMENT CHAPTER 20 Climate Change and Ozone

WHAT IS OZONE? Oxygen  At sea level, 21% of air is diatomic oxygen  Two oxygen atoms bonded together = O 2 Ozone  Triatomic form of oxygen (O 3 )  Three atoms of oxygen bonded together  Reactive molecule that is a strong oxidant and reacts with many materials in the atmosphere

WHAT IS OZONE? The Ozone Layer  About 90% of ozone in the atmosphere is found in the stratosphere  Absorbs most (about 99%)of the ultraviolet radiation heading towards Earth UV radiation comes in three forms UVC  Shortest wavelength  Most energetic  Absorbed strongly in atmosphere  Negligible UVC reaches surface of Earth

WHAT IS OZONE? UVA  Longest wavelength  Least energetic  Can cause some damage to living cells  Not affected by ozone and is transmitted to Earth UVB  Intermediate wavelength  Fairly energetic  Strongly absorbed by ozone layer  Damaging to living cells  THIS IS THE OZONE PROBLEM

THE PROBLEM British Antarctic Survey began measuring ozone in 1957  From 1957 to 1970 the ozone concentration was fairly stable  In 1984, the concentration took a sharp decline  Their research indicated that stratospheric ozone concentration has been decreasing Additional studies confirmed their reports Since then, this decline has been named the “Ozone Hole”  Not actually a hole  Relative depletion in the concentration of ozone that occurs during the Antarctic spring

THE PROBLEM Antarctic Hole  Each spring, the ozone in the Antarctic atmosphere decreases Amount of depletion has varied from 15% to 80% In general, the thickness of the ozone layer above the Antarctic each spring has been declining  Geographic area covered by the ozone hole continues to increase Covered 1 million or so square kilometers in 1970 Today it covers over 22 million square kilometers Larger than the entire U.S. and Canada combined In 2000, it covered over 28 million square kilometers  Arctic Hole Ozone depletion occurs over North Pole as well Troublesome because it tends to spread

CAUSES Hypothesis that ozone is being depleted by the presence of CHLOROFLUOROCARBONS (CFCs) was first suggested in 1974  CFCs have a long residence time in the lower atmosphere  CFCs eventually make their way to the upper atmosphere Here, they are destroyed by solar UV radiation This process produces chlorine, a highly reactive atom  Chlorine destroys ozone

CAUSES CFCs come from a variety of sources  Aerosol propellants in spray cans  Working gas in refrigeration and air-conditioning units  Foam-blowing process for production of styrofoam  Cleaning computer parts during manufacture Even if all manufacture, use and emission of ozone depleting chemical occurred today, the problem would not be solved  CFCs remain in atmosphere between 74 and 140 years  About 35% of certain types of CFCs will still be in air until 2100  Another 15% will be around till 2200  Some CFCs have not been emitted yet

EFFECTS OF DECREASED OZONE Marine Ecosystems  Phytoplankton form the foundation of aquatic food webs  Exposure to solar UVB radiation has been shown to negatively affect phytoplankton  One study has indicated a 6-12% reduction  This results in reduction in the size of the population of animals that eat these smaller creatures

EFFECTS OF DECREASED OZONE Plants  Plant growth can be directly affected by UVB radiation  May result in decreased production

EFFECTS OF DECREASED OZONE Biogeochemical Cycles  Increases in solar UV radiation could affect terrestrial and aquatic biogeochemical cycles  May result in increased levels of carbon dioxide (CO 2 ), and carbon monoxide (CO)  Could increase effects of global warming

EFFECTS OF DECREASED OZONE Materials  Synthetic polymers, naturally occurring biopolymers, as well as some other materials of commercial interest are adversely affected by solar UV radiation  Any increase in solar UVB levels will therefore accelerate their breakdown, limiting the length of time for which they are useful outdoors

EFFECTS OF DECREASED OZONE Human Health  Increases in type of skin cancer 1% decrease in ozone = 1% - 2% increase of UVB This will result in about 2% increase of skin cancer  Increase in a variety of diseases  Eye damage  Damage or reduce efficiency of human immune system

On The Trail of the Missing Ozone……