7. Ozone hole
1)
2)
3)
4)
5)
6)
7)
Structure of the ozone layer
Chemistry of the natural ozone layer
Recent changes to the ozone layer
Effects of Chlorine on global ozone reduction
Antarctic ozone depletion
Effects of enhanced UV-B radiation on life and ecosystems
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 O3 column)
그림자료출처: Atmospheric
Pollution(Jacobson, M. Z.)
2) Chemistry of the natural ozone layer
Chapman mechanism
O2  h  2O
<0.245m
O  O2  M  O3  M
O3  h  O  O2
<0.31 m
O3  O  2O2
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
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
자료출처 http://www.nnvl.noaa.gov/
2010 Jan 26
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 stratosphere
CFCl3+h-> CFCl2+Cl
<0.25m
CF2Cl2 +h -> CF2Cl+Cl <0.23m
Cl+O3-> ClO+O2
ClO+O-> Cl+O2
Upper and middle stratosphere
ClO+NO2+M-> ClONO2 +M
lower stratosphere
ClONO2, HCl: stable reservoir for Cl and ClO
5) Antarctic ozone depletion
• Discovery of Antarctic ozone hole: British scientists in 1985
• The effect on stratospheric ozone of chlorine released from manmade 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: http://jwocky.gsfc.nasa.gov/eptoms/dataqual/ozone_v8.html
그림자료출처: Atmospheric
Pollution(Jacobson, M. Z.)
그림자료출처: http://jwocky.gsfc.nasa.gov/eptoms/dataqual/ozone_v8.html
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 (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
http://www.atm.ch.cam.ac.uk/tour/
<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 phaseout 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