copyright © 2010 r. r. dickerson & z.q. li 1 aosc 620 ozone in the stratosphere r. dickerson...
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Copyright © 2010 R. R. Dickerson & Z.Q. Li
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AOSC 620Ozone in the Stratosphere
R. Dickerson
Note material on layers in general will be covered in AOSC 621.
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Layers in the atmosphere
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Actual depth of atmospheric layers.
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Why do we care about the UVB dosage? Cholesterol photolysis to Vitamin D
h
→
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Folate (vitamin B-9)
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Too little UV radiation means rickets;UV converts cholesterol to Vitamin D.
UVC - 100 to 290 nm UVB - 290 to 320 nm UVA - 320 to 400 nm
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Too much UV radiation causes skin cancer and photodissociates folate, also called Vitamin B9. Deficiency causes anemia and birth defects.
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The Stratospheric Ozone Layer
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From The Stratosphere 1981R. D. Hudson Editor
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O/O3 = j(O3)/(k2 M O2)
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The second catalytic cycle speeds up Reaction 4, that is it effectively increases k₄. Note that any loss of odd oxygen is the same as loss of ozone. These catalytic losses are still insufficient to explain the observed ozone concentration.
3) Crutzen (1970); Johnston (1971) “NOx”
Odd nitrogen or “NOx” is the sum of NO and NO₂. Often “NOx” is used as “odd nitrogen” which includes NO₃, HNO₃, 2 N₂O₅, HONO, PAN and other species. This total of “odd nitrogen” is better called “NOy” or “total reactive nitrogen.” N₂ and N₂O are unreactive.
NO + O₃ → NO₂ + O₂
O + NO₂ → NO + O₂
O + O₃ → 2O₂ NET
This is the major means of destruction of stratospheric ozone. The NOx cycle accounts for about 70% of the ozone loss at 30 km. We will calculate the implied steady ozone concentration later.
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4) Stolarski & Cicerone (1974); Wofsy & McElroy (1974) “ClOx”
Cl + O₃ → ClO + O₂
ClO + O → Cl + O₂
O + O₃ → 2O₂ NET
This reaction scheme is very fast, but there is not much ClOx in the stratosphere … yet. Molina and Rowland (1974) pointed out that CFC’s release Cl atoms. Today ClOx accounts for about 8% of the ozone loss at 30 km. If all these catalytic destruction cycles are added together, they are still insufficient to explain the present stratosphere O₃ level.
The general for of a catalytic ozone destruction cycle is:
X + O₃ → XO + O₂
XO + O → X + O₂
O + O₃ → 2O₂ NET
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The Stratospheric Ozone Layer
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How did Farby and Buisson do?
At 3000 Å (300 nm) 1/100 = I/Io = ln(-cl)
300 = 9.5 atm-1cm-1
-ln(0.01)/9.5 = 0.485 atm cm (compare to 0.50)
0.485 atm cm = 485 DU
Correct for zenith angle of 27o for Paris?
(cos 27o = 0.9 so = 432 DU.)
[O3] = 0.6 cm3 m-3 = 6x10-7 Is that right?
[O3] for uniform mixing ratio = column content/scale height
5 mm/8x106 mm = 6.25 x 10–7 = 625 ppb
As Fabry said this is too much for surface air, and the ozone layer lies above.
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Erythema Action Spectrum (red)Human squamous cell carcinoma (blue)
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