7. ozone hole 1)structure of the ozone layer 2) chemistry of the natural ozone layer 3)recent...

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  • 7. Ozone holeStructure of the ozone layer Chemistry of the natural ozone layerRecent changes to the ozone layerEffects of Chlorine on global ozone reductionAntarctic ozone depletionEffects of enhanced UV-B radiation on life and ecosystemsRegulation of CFCs

  • 1) Structure of the ozone layerDobson unit (DU): the thickness, in hundredth of millimeter, that the total ozone column would occupy at 0C and 1 atm

    ~300 DU ( Earths total atmospheric O3 column)

    : Atmospheric Pollution(Jacobson, M. Z.)

  • 2) Chemistry of the natural ozone layerChapman mechanism
  • : Atmospheric Pollution(Jacobson, M. Z.)

  • Brewer Dobson circulation: equator-to-pole circulation in the stratosphere

    : wikipedia

  • Catalytic chemical cycles

    Ozone destruction process

    X: H, OH, NO, Cl, Br

  • 3) Recent changes to the ozone layerAntarctic ozone hole

  • Arctic ozone dent

  • Ozone data from NOAA satellite2010 Sep 26 2010 Jan 26 http://www.nnvl.noaa.gov/

  • 4) Effects of Chlorine on global ozone reductionCFCs: invented in 1928 by Thomas Midgley Inexpensive, nontoxic, nonflammable, nonexplosive, insoluble, chemically unreactive under tropospheric conditions CFC-12 (CF2Cl2): propellant and refrigerant CFC-11(CFCl3): propellant and blowing agent Long lifetime (CFC-11:55yr, CFC-12:116 yr)

  • : Atmospheric Pollution(Jacobson, M. Z.)

  • Chlorine compound from natural source has short life time. => CFCs are responsible for most ozone destruction.Reactions in stratosphereCFCl3+h-> CFCl2+Cl CF2Cl+Cl ClO+O2ClO+O-> Cl+O2ClO+NO2+M-> ClONO2 +M lower stratosphereClONO2, HCl: stable reservoir for Cl and ClO Upper and middle stratosphere

  • 5) Antarctic ozone depletionDiscovery of Antarctic ozone hole: British scientists in 1985

    The effect on stratospheric ozone of chlorine released from man-made CFCs: Mario Molina and F. Sherwood Rowland

    1995 Nobel Prize: Crutzen, Molina, and RowlandO3 depletion: Antarctic Austral spring (October) 10~20km altitudeOzone hole area: ozone < 220 DUsClOx catalytic cycle: important in destroying O3 in middle and upper stratosphere Less important in the lower stratosphere The concentration of atomic oxygen is low

  • : Atmospheric Pollution(Jacobson, M. Z.): http://jwocky.gsfc.nasa.gov/eptoms/dataqual/ozone_v8.html

  • : http://jwocky.gsfc.nasa.gov/eptoms/dataqual/ozone_v8.html

  • Process leading to polar ozone depletionDuring the austral winterLack of solar heating over the AntarcticaLarge horizontal temperature gradient between the antarctic and the surrounding areaPolar vortex over the polar regionIsolate the air within polar vortexAir within polar vortex is extremely cold (below -80C)Polar stratospheric cloud (PSCs)

    On the surface of the ice particles in PSCs ClONO2(g)+HCl(s)-> Cl2 +HNO3(s) g:gas, s: solid(ice)

  • Ice particles that settle out from PSCs removes HNO3 from the stratosphere Cl2 increaseshttp://www.atm.ch.cam.ac.uk/tour/

  • In the Antarctic spring
  • Arctic stratosphere The Arctic winter stratosphere is generally warmer than the Antarctic by 10 K

    Overall lower frequency of PSC formation in the Arctic

    The PSCs tend to disappear several weeks before solar radiation penetrates the Arctic stratosphere

    Arctic polar vortex is less stable than that over the Antarctic.

  • 6) Effects of enhanced UV-B radiation on life and ecosystemssunburn of skin, skin cancer, cataract (), suppression of immune systemchange life-cycle timing and the rates of photosynthesis, and crop yields.increase photolysis rates of gases in troposphere

  • 7) Regulation of CFCs1974: Monila and Rowland hypothesized the effect of CFCs on ozone1987: Montreal Protocol- 27 countries signed limit the production of CFCs1992: Copenhagen Amendments-schedule the complete phase-out of CFCs in 1996

    CFCs: decreases or begin to level off due to regulationHCFCs and HFCs: increases

  • : Atmospheric Pollution(Jacobson, M. Z.)

  • sitehttp://jwocky.gsfc.nasa.gov/ : Total ozone mapping spectrometerhttp://ozonewatch.gsfc.nasa.gov/: Ozone hole watchhttp://www.atm.ch.cam.ac.uk/tour/index.html: The ozone hole tour University of Cambridgehttp://earthobservatory.nasa.gov/Features/Ozone/: Earth observatory