copyright © 2010 r. r. dickerson & z.q. li 1 aosc 620 ozone in the stratosphere r. dickerson...

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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copyright © 2010 r. r. dickerson & z.q. li 1 aosc 620 ozone in the stratosphere r. dickerson...

Documents

o net slide

o clo o clo o

nm slide

atmosphere slide

vitamin d h slide

present stratosphere

loss of ozone

ozone loss