November 18.docx

6 Pages

Environmental Studies
Course Code
EVS 205
James Rotenberg

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Intro to Stratospheric Ozone • Atmosphere contains layer of ozone that shields earth from UV radiation • Ozone absorbs all UV-C, most UV-B • UV-A is not affected by ozone • The shorted the wavelength the more energetic and dangerous to the UV Ozone hole—History and Discovery • Ozone Depletion: Effects o Ozone: thinned area over Antarctica in Blue  Reached record size o2 September 6, 2000 covering 11.5 million square miles (29.2 million km ) o Ozone Depletion most severe over Antarctica (but also Arctic) o Occurs annually in Antarctica between September-November o Not stationary due to weather patterns. o September 22, 2012—smallest in 20 years • Main Causes of Ozone Depletion o Main problem: CFCs o Other Chemicals:  Halons • Contain bromine and chlorine use in fire retardants  Methyl bromide • Pesticide  Methyl chloroform and Carbon tetrachloride • Industrial solvents used in production of pesticides  Nitrous Oxide • Released from burning fossil fuels o Ozone Depletion: Chemical Reaction  CFCs reach the atmosphere and react with UV light and O 3  O 3plits into O2+ O  CFC-Ozone reactions occurs more frequently than ozone formation  What does this mean eventually? • Ozone Hold Discovery o Joseph Farman—1985, Halley Bay, Antarctica (UK research base) o Measured Ozone layer in Dobsen Unites for about 30 years o Noticed decrease in total ozone in October for each year after mid 1970s • Satellite data for Zone Hole o Data and Ozone Hole had been recorded by satellites since the 1970s; however, the measurements were so low, they were automatically discarded by computers as error o Following Farman’s publication, data was reanalyzed and found correct o Publications  “Continued decline of total ozone over Halley, Antarctica since 1985” (Nature 376: 409-411—August 3, 2002)  Better News—NASA (Fall 2012—smallest ozone in 20 years) • Why Does Ozone Works? o Ozone absorbs at UV radiation at specific wavelengths o Absorbs most strongly at wavelengths of 250 nm  Called the “Hartley band” o Remember!  UV-C = 250-290 nm  Very hazardous and is completely absorbed • Ozone Threats o Chlorine: One of the most important catalysts for ozone destructions o Natural sources:  Mehyl chloride (CH 3l) • 25% of chlorine in stratosphere • Formed in the oceans by marine phytoplankton and from biomass burning in grasslands and forested areas  Hydrogen chloride (HCl) • Volcanoes • Anthropogenic Chlorine sources o Chlorocarbons  Family of chemicals usually derived from an organic compound o Halocarbons  Family of chemicals with halogen atoms • Chlorine, Fluorine, Bromine, Iodine  Include: • Carbon tetrachloride (CCl4)—solvent in dry cleaning • Chlorofluorocarbons (CFCs) Quantifying Ozone Concentration • Gordon Dobson o Dobson spectrophotometer: measures the amount of atmospheric ozone overhead by collection ultraviolet radiation scattered by the atmosphere • Dobson Units (DU) o Measures by the total number of O 3olecules un a 1cm column of air reaching from the ground16ut to space 2 o 1 DU = 2.7 x 10 O m3lecules/cm o On average the Earth has 250-300 DU of ozone coverage  Normally increases from equator to poles Variation of Ozone Layer Ozone and Light Spectrum • UV-A = 320-380 nm o UV-A completely penetrates ozone layer and reaches the ground. • UV-B = 290-320 nm o Biologically hazardous—Sunburn o Most is absorbed by ozone layer, but small amount reaches surface. • UV-C = 250=290 nm o Very hazardous! Completely absorbed by Ozone layer o CFCs • Past Uses o Refrigerators and air conditioners—Freon o Propellants in aerosol spray cans o Plastic foam bubble/peanuts—packaging o Cleaner solvents for electronic parts (computer chips) • Research finds CFCs harmful o 1973: Researchers from the University of California at Irvine found CFC as cause of Ozone depletion o 1985:  First discovered that Ozone thinning was observed to be greater than caused naturally  Battle with Dupont o 1988: Dupont acknowledged CFCs as cause of ozone depletion o 1995: Mario Molina, F. Sherwood Rowland, and Paul Crutzen win Nobel Prize in Chemistry. • Main Chemicals o CFC-11 (CFCl 3 o CFC-12 (CF Cl ) 2 2 o Originally designed as substitute refrigerants and also solvents. • CFCs—a continued Threat o Even though the production and use of CFCs have been banned, they continue to be a threat because of their “atmospheric lifetime” o CFC-11 (76 atm lifetime) o CFC-12 (139 atm lifetime) • The Life of a CFC Molecule o CFCs manufactured o CFC used and travel to lower atmosphere where they accumulate in the Troposphere  10 mt of chlorine present in the form of CFCs o Natural exchange of air between Troposphere and Stratosphere carries CFCs to upper atmosphere. o CFCs are exposed to UV radiation and are broken down releasing Chlorine products o These Chlorine products react with and destroy Ozone o Chlorine further reacts and forms less reactive compounds (HCl) o HCl travels downward to Troposphere and is carried away with rainwater. Unique Atmospheric Features at the Poles • Polar Vortex o Polar vortex is a swirling mass of very cold air that is isolated from the rest of the atmosphere for several months. o Ice crystals in this mass collect CFCs and other chemicals and set up conditions
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