7. Ozone hole 1)Structure of the ozone layer 2) Chemistry of the natural ozone layer 3)Recent changes to the ozone layer 4)Effects of Chlorine on global ozone reduction 5)Antarctic ozone depletion 6)Effects of enhanced UV-B radiation on life and ecosystems 7)Regulation of CFCs

1) Structure of the ozone layer Dobson unit (DU): the thickness, in hundredth of millimeter, that the total ozone column would occupy at 0  C and 1 atm ~300 DU ( Earth’s total atmospheric O 3 column) 그림자료출처 : Atmospheric Pollution(Jacobson, M. Z.)

2) Chemistry of the natural ozone layer Chapman mechanism <0.245  m <0.31  m Reproduce some of the broad featurees of the vertical distribution of O 3 in the stratosphere. Overpredict stratospheric O 3 concentration by about a factor of two in the tropics Underpredict O 3 concentration in middle to high latitudes

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

Brewer Dobson circulation: equator-to-pole circulation in the stratosphere 자료출처 : wikipedia

Catalytic chemical cycles Ozone destruction process X: H, OH, NO, Cl, Br

3) Recent changes to the ozone layer Antarctic ozone hole

Arctic ozone dent

Ozone data from NOAA satellite 2010 Sep Jan 26 자료출처

4) Effects of Chlorine on global ozone reduction CFCs: invented in 1928 by Thomas Midgley Inexpensive, nontoxic, nonflammable, nonexplosive, insoluble, chemically unreactive under tropospheric conditions CFC-12 (CF 2 Cl 2 ): propellant and refrigerant CFC-11(CFCl 3 ): propellant and blowing agent Long lifetime (CFC-11:55yr, CFC-12:116 yr)

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

Chlorine compound from natural source has short life time. => CFCs are responsible for most ozone destruction. Reactions in stratosphere CFCl 3 +h -> CFCl 2 +Cl <0.25  m CF 2 Cl 2 +h -> CF 2 Cl+Cl <0.23  m Cl+O 3 -> ClO+O 2 ClO+O-> Cl+O 2 ClO+NO 2 +M-> ClONO 2 +M lower stratosphere ClONO 2, HCl: stable reservoir for Cl and ClO Upper and middle stratosphere

5) Antarctic ozone depletion Discovery 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 Rowland O 3 depletion: Antarctic Austral spring (October) 10~20km altitude Ozone hole area: ozone < 220 DUs ClO x catalytic cycle: important in destroying O 3 in middle and upper stratosphere Less important in the lower stratosphere The concentration of atomic oxygen is low

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

Process leading to polar ozone depletion During the austral winter Lack of solar heating over the Antarctica Large horizontal temperature gradient between the antarctic and the surrounding area Polar vortex over the polar region Isolate the air within polar vortex Air within polar vortex is extremely cold (below -80  C) Polar stratospheric cloud (PSC s ) On the surface of the ice particles in PSC s ClONO 2 (g)+HCl(s)-> Cl 2 +HNO 3 (s) g:gas, s: solid(ice)

Ice particles that settle out from PSC s removes HNO 3 from the stratosphere Cl 2 increases /

In the Antarctic spring <0.45  m /

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 ecosystems sunburn of skin, skin cancer, cataract ( 백내장 ), suppression of immune system change life-cycle timing and the rates of photosynthesis, and crop yields. increase photolysis rates of gases in troposphere

7) Regulation of CFCs 1974: Monila and Rowland hypothesized the effect of CFCs on ozone 1987: Montreal Protocol- 27 countries signed limit the production of CFCs 1992: Copenhagen Amendments-schedule the complete phase-out of CFCs in 1996 CFCs: decreases or begin to level off due to regulation HCFCs and HFCs: increases

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

관련 site : Total ozone mapping spectrometerhttp://jwocky.gsfc.nasa.gov/ Ozone hole watchhttp://ozonewatch.gsfc.nasa.gov/ The ozone hole tourhttp:// University of Cambridge Earth observatoryhttp://earthobservatory.nasa.gov/Features/Ozone/