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This article explores ozone (O3) in both the troposphere and stratosphere, detailing how it is formed, its significance as an oxidant, and its detrimental effects on living organisms and the environment. It highlights the harmful impact of photochemical reactions and chlorofluorocarbons (CFCs) on ozone levels, particularly during the Antarctic spring, resulting in the so-called ozone hole. The text also presents the implications of ozone depletion on marine ecosystems and human health, including skin cancers and eye damage.
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1. O3 in the troposphere • Photo-chemical rxns produce O3 from NOx, HCs (VOCs), and O2 • O3 is a strong oxidant.
O3 in the troposphere • Causes eye & lung damage to mammals • Damages or kills leaves • Weakens or kills trees
2. O3 in Stratosphere • O3 forms when sunlight strikes O2 • O2 + O => O3 • About 90% of Earth’s O3 is in stratosphere
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 • 290 – 320 nm • 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 UVs • All is absorbed by O3 in stratosphere
Measuring O3 • Ground-based monitors & satellites • 1 ppb of ozone = 1 Dobson unit (DU)
Ozone should be balanced in the stratosphere constantly Except…..for the little problem of the ???
CFCs • Chlorofluorocarbons
4. Chlorofluorocarbon rxns • Cl3CF + UV Cl2 + Cl • (UV light strikes the CFC and splits it, releasing chlorine.) • Cl + O3 ClO + O2 • (The chlorine reacts with ozone to produce chlorine monoxide.) • ClO + O Cl + O2 • (The chlorine monoxide reacts with monatomic oxygen to produce chlorine again.)
Thus, CFCs create a chain reaction that stops the production of ozone. The chlorine is a catalyst that can be used over and over, breaking down as many as 100,000 O3 to O2.
CFCs • Are used during industrial processes & for refrigeration. • Are non-reactive, thus can drift for years, eventually in stratosphere.
Antarctic Winter • Dark & cold (< - 80º C) • Cold air descending (high pressure) • Coriolis effect sets up a strong westerly wind = a vortex • Vortex traps Antarctic air
Winter, continued… • Clouds of ice crystals form in stratosphere, providing surface area for CFC-O3 rxns • Clouds & winds are trapped within the vortex
Antarctic Spring • Increasing sunlight including UV • CFCs - O3 rxns increase • > 50% of stratospheric O3 is destroyed over Antarctica
As the Antarctic Spring ends… • Warming temps cause vortex to break up. • Ozone-rich air from the north floods into Antarctica • While ozone-depleted air flows northward over S. America, Australia, & New Zealand
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
Why the declines? Declines may be linked to warmer winter Antarctic temperatures. Climate Change?
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. • AND,
During the winter of 2013 – 2014, • The “Polar Vortex” wreaked havoc on most of our country (except us), bringing record storms and cold temperatures.
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
