Ozone Depletion

O 3 in troposphere Photo-chem rxns produce O 3 from NOx, HC and O 2 O 3 is a strong oxidant.

O 3 in troposphere Causes eye & lung damage to mammals Damages or kills leaves Weakens or kills trees

O 3 in stratosphere O 3 forms when sunlight strikes O 2 About 90% of Earth ’ s O 3 is in stratosphere

UV

UV-A UV-A is 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

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

UV-C UV-C is nm (shortest of the UV) Most energetic of the UV ’ s All is absorbed by O 3 in stratosphere

Measuring O 3 Ground-based monitors & satellites 1 ppb of ozone = 1 Dobson unit (DU)

Ozone should be added to the stratosphere constantly But…..for the little problem of the CFCs

Chloro-fluoro-carbon rxns Cl 3 CF + UV  Cl 2 + Cl Cl + O 3  ClO + O 2 ClO + O  Cl + O 2

Thus, CFCs stop the production of ozone.

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

Antarctic O 3 depletion

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

mid-May continued Clouds of ice crystals form in stratosphere, providing surface area for CFC-O 3 rxns Clouds & winds trapped within vortex

Oct – Nov (springtime) Increasing sunlight including UV CFCs - O 3 rxns increase > 50% of stratospheric O 3 is destroyed over Antarctica

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

Ozone hole

Ozone “ hole ” Not really a hole; more of a thinning. Defined as concentrations of O3 < 200 ppb Occurs during Antarctic spring (Sept-Nov)

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 mkm 2 in 2005

Why the declines? Declines may be linked to warmer winter Antarctic temperatures. Global warming?

Ozone trends (1) Depletion probably began mid 1970s (2) Sulfate aerosol emissions from the 1991 Mt Pinatubo eruptions probably caused greater depletion

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.

(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

Ozone trends continued (5) The energy of > UV-B at Earth ’ s surface causes > formation of surface O 3.

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.

Effects of O 3 depletion

Marine food chains > UV causes decline in productivity of polar phytoplankton Equatorial phytoplankton have adaptations for UV, no surprise

UV Damage to Humans (1) Clouding of eye ’ s cornea  cataracts

(2) Basal carcinoma

Basal carcinoma

(3) Melanoma

(4) Changes to DNA

Is a suntan really a good idea? (5) Wrinkles

As long as O 3 depletion continues, It would be a good idea to add a few things to your self-survival kit.

The end