7. Ozone hole
1) Structure of the ozone layer2) Chemistry of the natural ozone layer3) Recent changes to the ozone layer4) Effects of Chlorine on global ozone reduction5) Antarctic ozone depletion6) Effects of enhanced UV-B radiation on life and ecosystems7) 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 0C and 1 atm
• ~300 DU ( Earth’s total atmospheric O3 column)
그림자료출처 : Atmospheric Pollution(Jacobson, M. Z.)
2) Chemistry of the natural ozone layer
Chapman mechanism <0.245m
<0.31 m
Reproduce some of the broad featurees of the vertical distribution of O3 in the stratosphere.
Overpredict stratospheric O3 concentration by about a factor of two in the tropics
Underpredict O3 concentration in middle to high latitudes
23
23
32
2
2
2
OOO
OOhO
MOMOO
OhO
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 26 2010 Jan 26
자료출처 http://www.nnvl.noaa.gov/
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 (CF2Cl2): propellant and refrigerant
• CFC-11(CFCl3): 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 stratosphereCFCl3+h-> CFCl2+Cl <0.25m
CF2Cl2 +h -> CF2Cl+Cl <0.23m
Cl+O3-> ClO+O2
ClO+O-> Cl+O2
ClO+NO2+M-> ClONO2 +M lower stratosphere
ClONO2, 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• O3 depletion: Antarctic Austral spring (October) 10~20km altitude• Ozone hole area: ozone < 220 DUs• • ClOx catalytic cycle: important in destroying O3 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 : http://jwocky.gsfc.nasa.gov/eptoms/dataqual/ozone_v8.html
그림자료출처 : http://jwocky.gsfc.nasa.gov/eptoms/dataqual/ozone_v8.html
Process leading to polar ozone depletion
• During 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 increases
http://www.atm.ch.cam.ac.uk/tour/
• In the Antarctic spring <0.45m
http://www.atm.ch.cam.ac.uk/tour/
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
• http://jwocky.gsfc.nasa.gov/ : Total ozone mapping spectrometer
• http://ozonewatch.gsfc.nasa.gov/: Ozone hole watch• http://www.atm.ch.cam.ac.uk/tour/index.html: The ozone
hole tour University of Cambridge• http://earthobservatory.nasa.gov/Features/Ozone/: Earth
observatory
