A tour of the ozone holeCourtesy of the Centre for Atmospheric Sciences,

Cambridge Universityand

www.solcomhouse.complus 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• 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

• 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_mp

eg/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 foam-

blowing agents

• halogen compounds - Fire fighters used bromine-containing 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

• 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?

• 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?• 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

• 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 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

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 ozone-destroying 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

Distinct latitudinal distribution

Quite deadly

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

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