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 Turco’s
“Earth Under Siege”
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
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
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
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
How is ozone formed?
UV radiation strikes the O2 molecule and splits it, atomic oxygen
associates itself with another O2 molecule – simplistic version
Climatology of ozone
Annual cycle
Mean climatology
Synoptic variability of ozone
Ozone also has substantial variability on smaller time scale
Vertical variation of ozone
Source, sink and reservoirs
Ozone is in a fluid state of creation and destruction
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
“Chapman Reactions”
•
Ozone is formed by:
O2 + hv -> O + O
(1)
•
Ozone can reform resulting in no net loss of ozone:
O3 + hv -> O2 + O
(3)
O + O2 -> O3
(2)
•
Ozone is also destroyed by the following reaction:
O + O3 -> O2 + O2
(4)
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
Chemical processes
 ozone depletion
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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
Not there yet • We still have many more atoms ozone than
active chlorine
• How do we destroy all the ozone??
One more step:
• Only have molecular chlorine (Cl2)
• Require atomic chlorine to destroy ozone
• Via “photodissociation”
• Cl2 + hv -> Cl + Cl
• Key to timing of ozone hole
• Finally – catalytic destruction of ozone
Final stage
• Catalytic cycle – molecules significantly
changes or enables a reaction cycle without
being altered by the cycle itself
Ozone loss recipe - summary
• Polar winter  polar vortex  isolates air within
• Cold temperatures  Polar Stratospheric Clouds
 vortex air isolated  cold temperatures &
PSC’s 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
The Antarctic polar vortex
Ozone loss over Antarctica
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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
Evolution ClONO2 – North Pole –
winter 1994
• http://www.atm.ch.cam.ac.uk/tour/tour_mpe
g/anim_clono2.mpg
• Winter – no light – ClONO2 destroyed –
sunlight returns – ClONO2 recovery – edge
vortex – doughnut shape – ‘chlorine nitrate
collar’
What causes the depletion?
• release of manmade chemicals –
• CFC - refrigerants, aerosol sprays, solvents and foamblowing agents
• halogen compounds - Fire fighters used brominecontaining halogens to put out fires
• NOx
One chlorine atom - average - destroys one thousand
ozone molecules before converted into form harmless
to ozone
Atmospheric Chlorine cycle
Vertical Structure of Ozone Cycle
CFCs and Ozone depletion
Reservoirs
Reactions
Nitrous oxide cycle
Ozone depletion through
nitrous oxide
Sources that harm ozone layer
Sources of chloroflurocarbons
Total ozone – October monthly averages
Halley Bay, Antarctica
Monthly averages for October
TOMS Satellite Measurements
• Total Ozone Mapping
Spectrometer
• Based on backscattered light
• UV range
• Dobson units (DU)
Ozone Hole –
Sept 22-Oct 6 2002 & 2003
Ozone hole size
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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
Need for a cold dark place…..
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)
Is the ozone loss only in Antarctica?
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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
Why is the loss more dramatic at
the poles?
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Polar meteorology
Polar vortex – winter polar night
Polar stratospheric clouds (-80C)
nitric acid trihydrate
Chemical reactions
• occur on surface PSC’s
• Occur very fast
What drives the vortex?
Vortex explanation
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mid-May - onset SH winter
Antarctic stratosphere cools
descends closer to the surface
Coriolis effect - sets up strong westerly
circulation (@ SP)
• forms oblong vortex
• temperatures - lower stratosphere cool < 80C  PCS’s
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.
Arctic ozone hole?
What does this look like on
population density map?
Any satellite evidence?
May 25, 2000 – “low ozone event”
What do these clouds look like?
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
Why the different response?
• Polar stratospheric clouds surfaces where
benign forms of chlorine  reactive ozonedestroying 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
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
Ozone losses in mid-latitudes
• What causes these losses?
• Are losses over poles linked with those of
mid latitudes?
• Are CFC’s and bromine also responsible?
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
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
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
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 ozonedestroying power of polar stratospheric clouds
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
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
Schematic of chemical model
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
Comparison of model output and
satellite observation
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
UV, ozone and melanoma
Quite deadly
Distinct latitudinal
distribution
And . . . elevated risk of
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herpes viruses
human immunodeficiency virus HIV- 1
variety of papilloma viruses
leishmaniasis
malaria
forms of tuberculosis
leprosy
lupus erthematodes
dermatitis
E. coli
Staphylococcus aureus
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
And . .
• damages DNA marine bacteria, starfish
and urchins larvae
• alters ocean chemistry
Ozone hole 2003
Visit:
http://www.theozonehole.com/ozonehole2003
.htm