A tour of the ozone hole

1
A tour of the ozone hole

• Courtesy of the Centre for Atmospheric Sciences,
• Cambridge University
• and
• www.solcomhouse.com
• plus Claire Cosgrove and Peter Webster (EAS)
• with liberal use of Rich Turcos
• Earth Under Siege

2
History of the Ozone Discovery

• Dramatic loss of ozone in the lower stratosphere
  over Antarctica was first noticed in the 1970s by
  a research group
• from the British Antarctic Survey (BAS) who
  were monitoring the atmosphere above Antarctica

3
What is the ozone hole?

• News media confuses it with the problem of global
  warming
• ozone contributes to the greenhouse effect
• over Antarctica (and the Arctic), stratospheric
  ozone depleted over past 15 years at certain
  times of the year
• hole presently size Antarctica, 10km altitude -
  lower stratosphere

4
What is ozone?

• Ozone forms a layer in the stratosphere, thinnest
  in the tropics (around the equator) and denser
  towards the poles
• measured in Dobson units (DU)
• 260 DU near the tropics

5
What is a Dobson unit?

• 1 Dobson Unit (DU) is defined to be 0.01 mm
  thickness at STP - (0C and 1 atmos press).
• A slab 3mm thick corresponds to 300 DU

6
How is ozone formed?
UV radiation strikes the O2 molecule and splits
it, atomic oxygen associates itself with another
O2 molecule simplistic version
7
Climatology of ozone
Mean climatology
Annual cycle
8
Synoptic variability of ozone
Ozone also has substantial variability on smaller
time scale
9
Vertical variation of ozone
10
Source, sink and reservoirs
Ozone is in a fluid state of creation and
destruction
11
How ironic . . .

• at ground level, ozone is a health hazard
• major constituent of photochemical smog
• in the stratosphere, it absorbs potentially
  harmful ultra-violet (UV 240-320nm harmful)
  radiation
• Protects from skin cancer, etc

12
Chapman Reactions

• Ozone is formed by
• O2 hv -gt O O
• 
  (1)
• Ozone can reform resulting in no net loss of
  ozone
• O3 hv -gt O2 O
• 
  (3)
• O O2 -gt O3
• 
  (2)
• Ozone is also destroyed by the following
  reaction
• O O3 -gt O2 O2
• 
  (4)

13
Comparison of reactions

• Reaction (2) slower with increasing altitude
• Reaction (3) faster with increasing altitude
• Lower in stratosphere, atmosphere denser, UV
  absorption increases ozone peaks 20km
• Closer to surface, UV level decr, ozone decr

14
Chemical processes ? ozone depletion

• Chlorine, bromine from human activities
• Chlorine carriers hydrochloric acid, chlorine
  nitrate
• Other impt cpds nitric acid, dinitrogen
  pentoxide
• Right conditions necessary for chemical reactions
  to occur
• On surface of PSC
• Denoxification slows removal ClO

15
Not there yet -

• We still have many more atoms ozone than active
  chlorine
• How do we destroy all the ozone??

16
One more step

• Only have molecular chlorine (Cl2)
• Require atomic chlorine to destroy ozone
• Via photodissociation
• Cl2 hv -gt Cl Cl
• Key to timing of ozone hole
• Finally catalytic destruction of ozone

17
Final stage

• Catalytic cycle molecules significantly changes
  or enables a reaction cycle without being altered
  by the cycle itself

18
Ozone loss recipe - summary

• Polar winter ? polar vortex ? isolates air within
• Cold temperatures ? Polar Stratospheric Clouds ?
  vortex air isolated ? cold temperatures PSCs
  persist
• Heterogeneous reactions allow reservoir species
  of chlorine bromine - rapidly converted to more
  active forms.
• No ozone loss until sunlight returns ? production
  active chlorine ? initiates catalytic ozone
  destruction ? ozone loss rapid

19
The Antarctic polar vortex
20
Ozone loss over Antarctica

• most dramatic in the lower stratosphere
• nearly all the ozone depleted
• area the size of Antarctica
• many km thick
• most pronounced in spring/October
• persists two months
• December moves ? Falklands, S Georgia, S Am

21
Evolution ClONO2 North Pole winter 1994

• http//www.atm.ch.cam.ac.uk/tour/tour_mpeg/anim_cl
  ono2.mpg
• Winter no light ClONO2 destroyed sunlight
  returns ClONO2 recovery edge vortex
  doughnut shape chlorine nitrate collar

22
What causes the depletion?

• release of manmade chemicals
• CFC - refrigerants, aerosol sprays, solvents and
  foam-blowing agents
• halogen compounds - Fire fighters used
  bromine-containing halogens to put out fires
• NOx

23
One chlorine atom - average - destroys one
thousand ozone molecules before converted into
form harmless to ozone
24
Atmospheric Chlorine cycle
25
Vertical Structure of Ozone Cycle
26
CFCs and Ozone depletion
Reservoirs
Reactions
27
Nitrous oxide cycle
28
Ozone depletion through nitrous oxide
29
(No Transcript)
30
Sources that harm ozone layer
31
Sources of chloroflurocarbons
32
Total ozone October monthly averages
Halley Bay, Antarctica
33
Monthly averages for October
34
TOMS Satellite Measurements

• Total Ozone Mapping Spectrometer
• Based on backscattered light
• UV range
• Dobson units (DU)

35
(No Transcript)
36
Ozone Hole Sept 22-Oct 6 2002 2003
37
Ozone hole size

• 1.5 x USA
• Australia 8,923,000
• USA 9,363,130
• Europe 10,498,000
• Antarctica 13,340,000
• Russia 17,078,000
• N America 25,349,000
• Africa 30,355,000 sq km

38
Need for a cold dark place..
39
What is being done?

• First global agreement - restrict CFCs - Montreal
  Protocol - 1987
• European Community countries have even stricter
  measures
• Was anticipated - recovery of the ozone layer
  within 50 years of 2000 World Meteorological
  Organisation (WMO reports 25, 37)

40
Is the ozone loss only in Antarctica?

• Arctic low ozone event
• S America from Antarctica hole
• Volcanic ozone hole
• European ozone hole - heavily populated northern
  mid-latitudes (30-60N) formation smaller, much
  slower

41
Why is the loss more dramatic at the poles?

• Polar meteorology
• Polar vortex winter polar night
• Polar stratospheric clouds (-80C)
• nitric acid trihydrate
• Chemical reactions
• occur on surface PSCs
• Occur very fast

42
What drives the vortex?
43
Vortex explanation

• mid-May - onset SH winter
• Antarctic stratosphere cools
• descends closer to the surface
• Coriolis effect - sets up strong westerly
  circulation (_at_ SP)
• forms oblong vortex
• temperatures - lower stratosphere cool lt -80C ?
  PCSs

44
South American Ozone

• The Ozone hole has reached Argentina, Chile and
  The Falkland Islands since the 1990's.
• Ozone levels dropped down 70 in some areas.
• The protective level of ozone dropped below 150
  DU in some areas.

45
(No Transcript)
46
Arctic ozone hole?
47
What does this look like on population density
map?
48
Any satellite evidence?
May 25, 2000 low ozone event
49
What do these clouds look like?
50
Implications of low ozone event

• Could be blown south by high-altitude winds
  across heavily populated regions
• 10 reduction ozone layer ? 25 imcr
  non-melanoma skin cancer temperate climates by
  2050
• Arctic ozone recovery may not be as quick as
  Antarctic

51
Why the different response?

• Polar stratospheric clouds surfaces where benign
  forms of chlorine ? reactive ozone-destroying
  forms
• Remove nitrogen compounds that moderate
  destructive impact of chlorine - Dr. Phil De
  Cola, Atmospheric Chemistry Program Manager, NASA
  Headquarters, Washington, DC.
• Presently nitric acid stays longer in Arctic
  reduces amount reactive chlorine

52
Any links with global warming?

• Upper atmosphere is getting colder due to
• Ozone loss
• Greenhouse gases warming at surface ? cooling
  upper atmosphere
• ? Arctic ozone hole forming within 20y Professor
  Jonathan Shanklin,The British Antarctic Study

53
Ozone losses in mid-latitudes

• What causes these losses?
• Are losses over poles linked with those of mid
  latitudes?
• Are CFCs and bromine also responsible?

54
European Ozone

• Upper atmospheric conditions in The Northern
  Hemisphere are becoming similar to those of the
  Antarctic. The result of this could be the
  formation of an "Arctic Ozone Hole" or more
  correctly termed "low ozone event". 
• 10 ozone decr winter
• 5 ozone decr - summer

55
November 11,2001

• Levels of ozone - fall to 60-70 of the seasonal
  average -Climate Research Centre, KNMI, The
  Netherlands.

Low ozone event maybe caused by unusual air
currents not chemicals as Antarctic ozone hole
56
Volcanic Ozone Hole?

• An "ozone hole" could form over the North Pole
  after future major volcanic eruptions within
  next 30 years - Azadeh Tabazadeh, scientist at
  NASA's Ames Research Center, Moffett Field, Calif
• winter stratosphere temperatures highly variable
  in Arctic
• If a period of high volcanic activity coincides
  with a series of cold Arctic winters

57
How would this happen?

• Large volcanic eruptions - pump sulfur compounds
  into atmosphere.
• Compounds form sulfuric acid clouds - similar
  polar stratospheric clouds - nitric acid and
  water.
• Form in upper atmosphere - very cold conditions
  - destruction of ozone over poles.
• Volcanic sulfuric acid clouds add to the
  ozone-destroying power of polar stratospheric
  clouds

58
Global implications

• Could volcanic aerosols cause ozone destruction
  in warmer regions of the globe?
• Could ozone destruction occur at lower altitude
  corresponding with level of volcanic aerosol?
• YES 1993 Artic winter not extremely cold but
  ozone loss was very high why? sulphurous
  Pintatubo clouds at lower altitude

59
Chemical modelling

• 'blow' (or advect) chemical species around the
  globe using known or computed weather patterns -
  winds, temperatures and pressures
• rates of chemical reactions dependent on
  temperature, pressure, and with photolytic
  processes, the position of the sun

60
Schematic of chemical model
61
Different types of models

• Box model single point only chemistry
  simulated cheap model
• Trajectory model trajectory box model that
  moves wind fields ? path
• 3-D model grid of box models with vertical
  levels- more realistic meteorology - complex

62
Comparison of model output and satellite
observation
63
Health Consequences

• Skin cancers, sunburn, eye damage, cataracts
• estimated 10 reduction ozone layer ? 25
  increase non-melanoma skin cancer -temperate
  latitudes by 2050
• Suppress immune system
• DNA mutation of existing disease bacteria and
  viruses

64
UV, ozone and melanoma
Quite deadly
Distinct latitudinal distribution
65
(No Transcript)
66
(No Transcript)
67
And . . . elevated risk of

• herpes viruses
• human immunodeficiency virus HIV- 1
• variety of papilloma viruses
• leishmaniasis
• malaria
• forms of tuberculosis
• leprosy
• lupus erthematodes
• dermatitis
• E. coli
• Staphylococcus aureus

68
Biological Consequences

• Biologically damaging young, new shoots
• Southern Ocean - most productive marine ecosystem
  - less phytoplankton (8.5per cent decr)- food for
  microscopic animals - eaten by krill sustain
  seals, penguins, and baleen whales
• 6 ozone depletion ? loss 7 million tons fish
  per year

69
And . .

• damages DNA marine bacteria, starfish and
  urchins larvae
• alters ocean chemistry

70
Ozone hole 2003

• Visit
• http//www.theozonehole.com/ozonehole2003.htm