Transcript Ozone Depletion - Iowa State University

Ozone Depletion
J(Hans) van Leeuwen
Stratospheric ozone and its importance
– The hole story
Solar Spectrum
The Ultraviolet Spectrum
400nm
Radio
 UV light: 100 to 400 nm
IR
Visible
Light
100nm
UV
X-Rays
l
UV-A
UV-B
UV-C
Far UV
UV spectrum – 4 regions
o Far UV: 100 – 200 nm
o UV – C : 200 – 280 nm
o UV – B : 280 – 315 nm
o UV – A : 315 – 400 nm
300nm
200nm
DNA damaging range
DNA Damaging Range of UV Light
Ultraviolet Radiation
230-280 nm damages nucleic acids
Stops reproduction of cells by
breaking apart the DNA bonds
Ozone production peaks at 185nm
Ozone absorbance and destruction at 200-320nm
Ozone formation

Ozone destruction

UV ozone generation
and destruction: equilibrium
O2 + h185
 2O.
O. + O 2 + M  O3 + M
O3 + h254
 O2 + O .
Equilibrium between
production and
destruction
Atmospheric Layers
Ozone Formation and Depletion
The catalyzed cycle of stratospheric
ozone production and destruction
1. h + O2  2O.
2. O. + O2  O3
3. O3 + X  O2 + OX
4. OX + O.  O2 + X
X could be Cl from a CFC
Halogen catalysis of ozone destruction
Halogen removal from
atmosphere
Cl + CH4  HCl + CH3.
ClO + NO2  ClONO2
Both HCl and ClONO2 inactive: rain out
Br + O3  BrO + O2
Br + CH4  HBr + CH3.
HBr can photolytically provide Br again
Halons and CH3Br provide Br
Ozone Depleting Substances
List of ozone
depleting substances Table 8.13 Masters
http://www.epa.gov/ozone/ods.html
Halons
Antarctic Ozone Problems
Antarctic Vortex during Winter
Ice crystals
form in vortex
Strong circulatory
winds around
Antarctica isolate the
air in the lower and
middle stratosphere
Antarctic Reactions
Winter reactions
Polar vortex: -90 oC  Ice clouds
ClONO2 + H2O
 HOCl + HNO3
HOCl + HCl  Cl2 + H2O
Spring reactions
Cl2 + h  2 Cl in early spring
Cl + O3  ClO + O3 destructive loop
HNO3 + Cl  ClONO2 in photocatalysis
Ozone in Stratosphere:
Dobson Units (DU)
If 100 DU of ozone were brought to the
Earth's surface, it would form a layer 1
millimeter thick. In the tropics, ozone
levels are typically between 250 and 300
DU year-round. In temperate regions,
seasonal variations can produce large
swings in ozone levels. For instance,
measurements in Leningrad have
recorded ozone levels as high as 475
DU and as low as 300 DU.
Record ozone hole, 2006
Ozone hole altitude profile
Ozone hole severity
Ozone hole extent
Global total ozone change
http://jwocky.gsfc.nasa.gov/
The Nobel Prize in Chemistry 1995
Paul J. Crutzen
Mario J. Molina
F. Sherwood Rowland
The Netherlands
USA
USA
Max-Planck-Institute
for Chemistry Mainz, Germany
MIT, USA
Cambridge, MA
Department of Chemistry,
University of California
Irvine, CA, USA
1933 -
1943 -
1927 -
"for their work in atmospheric chemistry,
particularly concerning the formation and
decomposition of ozone"
Ozone Hole Growth: 29y
October 27, 1980
September 21, 2006
September 17, 2009
http://www.youtube.com/watch?v=brblHxZctsA
Ozone Hole 2009
Ozone Hole 2009
Ozone Hole 2009
Ozone hole size in recent years
http://www.cmdl.noaa.gov/ozwv/ozsondes/spo/ozone_anim2004.html