Ozone Depletion

O3 in troposphere Photo-chem rxns produce O3 from NOx, HC and O2 O3 is a strong oxidant.

O3 in troposphere Causes eye & lung damage to mammals Damages or kills leaves Weakens or kills trees

O3 in stratosphere O3 forms when sunlight strikes O2 About 90% of Earth’s O3 is in stratosphere

UV

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 O3 doesn’t absorb UV-A

UV-B UV-B is most harmful to cells Most UV-B absorbed by O3, some reaches Earth’s surface O3 depletion has increased UV-B at Earth’s surface

UV-C UV-C is 100 - 290 nm (shortest of the UV) Most energetic of the UV’s All is absorbed by O3 in stratosphere

Measuring O3 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 Cl3CF + UV  Cl2 + Cl Cl + O3  ClO + O2 ClO + O  Cl + O2

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 O3 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-O3 rxns Clouds & winds trapped within vortex

Oct – Nov (springtime) Increasing sunlight including UV CFCs - O3 rxns increase > 50% of stratospheric O3 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 km2 in 1998 (3rd) 29.5 mkm2 in 2000 (largest) 28.7 mkm2 in 2003 (2nd largest) 24.3 mkm2 in 2004 25.9 mkm2 in 2005

Declines may be linked to warmer winter Antarctic temperatures. 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 (4) Industrials areas have more ozone at surface levels. Ozone absorbs UV and may be why scientists can’t find increased levels of O3 in Northern Hemisphere

Ozone trends continued (5) The energy of > UV-B at Earth’s surface causes > formation of surface O3.

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 O3 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? Wrinkles

As long as O3 depletion continues, It would be a good idea to add a few things to your self-survival kit.

The end