ozone hole w notes

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Information about ozone hole w notes

Published on February 20, 2008

Author: Modest

Source: authorstream.com

A tour of the ozone hole:  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:  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?:  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?:  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?:  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?:  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:  Climatology of ozone Annual cycle Mean climatology Synoptic variability of ozone:  Synoptic variability of ozone Ozone also has substantial variability on smaller time scale Vertical variation of ozone:  Vertical variation of ozone Source, sink and reservoirs:  Source, sink and reservoirs Ozone is in a fluid state of creation and destruction How ironic . . .:  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”:  “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:  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:  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 - :  Not there yet - We still have many more atoms ozone than active chlorine How do we destroy all the ozone?? One more step::  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:  Final stage Catalytic cycle – molecules significantly changes or enables a reaction cycle without being altered by the cycle itself Ozone loss recipe - summary:  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:  The Antarctic polar vortex Ozone loss over Antarctica:  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:  Evolution ClONO2 – North Pole – winter 1994 http://www.atm.ch.cam.ac.uk/tour/tour_mpeg/anim_clono2.mpg Winter – no light – ClONO2 destroyed – sunlight returns – ClONO2 recovery – edge vortex – doughnut shape – ‘chlorine nitrate collar’ What causes the depletion?:  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:  One chlorine atom - average - destroys one thousand ozone molecules before converted into form harmless to ozone Atmospheric Chlorine cycle:  Atmospheric Chlorine cycle Slide25:  Vertical Structure of Ozone Cycle CFCs and Ozone depletion:  CFCs and Ozone depletion Reservoirs Reactions Nitrous oxide cycle:  Nitrous oxide cycle Ozone depletion through nitrous oxide:  Ozone depletion through nitrous oxide Sources that harm ozone layer:  Sources that harm ozone layer Sources of chloroflurocarbons:  Sources of chloroflurocarbons Total ozone – October monthly averages:  Total ozone – October monthly averages Halley Bay, Antarctica Monthly averages for October:  Monthly averages for October TOMS Satellite Measurements:  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 – Sept 22-Oct 6 2002 & 2003 Ozone hole size:  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…..:  Need for a cold dark place….. What is being done?:  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?:  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?:  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?:  What drives the vortex? Vortex explanation:  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:  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?:  Arctic ozone hole? What does this look like on population density map?:  What does this look like on population density map? Any satellite evidence?:  Any satellite evidence? May 25, 2000 – “low ozone event” What do these clouds look like?:  What do these clouds look like? Implications of ‘low ozone event’:  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?:  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?:  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:  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:  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:  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?:  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?:  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 :  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:  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:  Schematic of chemical model Different types of models:  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:  Comparison of model output and satellite observation Health Consequences :  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:  UV, ozone and melanoma Distinct latitudinal distribution Quite deadly And . . . elevated risk of:  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:  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 . . :  And . . damages DNA marine bacteria, starfish and urchins larvae alters ocean chemistry Ozone hole 2003:  Ozone hole 2003 Visit: http://www.theozonehole.com/ozonehole2003.htm

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