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Published byEdward Long Modified over 8 years ago
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Ozone Depletion
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O 3 in troposphere Photo-chem rxns produce O 3 from NOx, HC and O 2 O 3 is a strong oxidant.
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O 3 in troposphere Causes eye & lung damage to mammals Damages or kills leaves Weakens or kills trees
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O 3 in stratosphere O 3 forms when sunlight strikes O 2 About 90% of Earth ’ s O 3 is in stratosphere
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UV
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UV-A UV-A is 320 - 400 nm (longest of the UV) Least energetic of the UV, causes some cell damage All UV-A reaches Earth ’ s surface O 3 doesn ’ t absorb UV-A
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UV-B UV-B is most harmful to cells Most UV-B absorbed by O 3, some reaches Earth ’ s surface O 3 depletion has increased UV-B at Earth ’ s surface
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UV-C UV-C is 100 - 290 nm (shortest of the UV) Most energetic of the UV ’ s All is absorbed by O 3 in stratosphere
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Measuring O 3 Ground-based monitors & satellites 1 ppb of ozone = 1 Dobson unit (DU)
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Ozone should be added to the stratosphere constantly But…..for the little problem of the CFCs
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Chloro-fluoro-carbon rxns Cl 3 CF + UV Cl 2 + Cl Cl + O 3 ClO + O 2 ClO + O Cl + O 2
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Thus, CFCs stop the production of ozone.
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CFCs Are used during industrial processes & for refrigeration. Are non-reactive, thus can drift for years, eventually in stratosphere. The chlorine is a catalyst that can be used over & over, as many as 100,000 O3 O2
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Antarctic O 3 depletion
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mid-May (winter) Dark & cold (< - 80º C) Cold air descending (high pressure) Coriolis effect sets up a strong westerly wind (counter-clockwise) = a vortex Vortex traps Antarctic air
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mid-May continued Clouds of ice crystals form in stratosphere, providing surface area for CFC-O 3 rxns Clouds & winds trapped within vortex
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Oct – Nov (springtime) Increasing sunlight including UV CFCs - O 3 rxns increase > 50% of stratospheric O 3 is destroyed over Antarctica
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mid-December (end of spring) Warming temps cause vortex to break up. Ozone-rich air from the north floods into Antarctica While ozone-depleted air flows northward into S. America & New Zealand
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Ozone hole
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Ozone “ hole ” Not really a hole; more of a thinning. Defined as concentrations of O3 < 200 ppb Occurs during Antarctic spring (Sept-Nov)
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At its “ peak ” in September, the ozone hole was 27.2 million km 2 in 1998 (3 rd ) 29.5 mkm 2 in 2000 (largest) 28.7 mkm 2 in 2003 (2 nd largest) 24.3 mkm 2 in 2004 25.9 mkm 2 in 2005
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Why the declines? Declines may be linked to warmer winter Antarctic temperatures. Global warming?
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Ozone trends (1) Depletion probably began mid 1970s (2) Sulfate aerosol emissions from the 1991 Mt Pinatubo eruptions probably caused greater depletion
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Ozone trends continued (3) At polar latitudes, sun is lower in sky and light passes through more atmosphere. Thus, less UV reaches surface at polar latitudes.
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(4) Industrials areas have more ozone at surface levels. Ozone absorbs UV and may be why scientists can ’ t find increased levels of O 3 in Northern Hemisphere
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Ozone trends continued (5) The energy of > UV-B at Earth ’ s surface causes > formation of surface O 3.
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Why no ozone “ hole ” at North Pole? Warmer temps compared to S. Pole Jet stream tends to meander rather than creating vortex However, recent measurements show 5% O3 depletion over North Pole.
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Effects of O 3 depletion
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Marine food chains > UV causes decline in productivity of polar phytoplankton Equatorial phytoplankton have adaptations for UV, no surprise
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UV Damage to Humans (1) Clouding of eye ’ s cornea cataracts
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(2) Basal carcinoma
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Basal carcinoma
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(3) Melanoma
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(4) Changes to DNA
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Is a suntan really a good idea? (5) Wrinkles
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As long as O 3 depletion continues, It would be a good idea to add a few things to your self-survival kit.
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The end
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