Copyright © 2010 R. R. Dickerson & Z.Q. Li 1 AOSC 620 Ozone in the Stratosphere R. Dickerson Note material on layers in general will be covered in AOSC 621.

Copyright © 2013 R. R. Dickerson & Z.Q. Li 2 Layers in the atmosphere

Copyright © 2013 R. R. Dickerson & Z.Q. Li 3 Actual depth of atmospheric layers.

Copyright © 2013 R. R. Dickerson & Z.Q. Li 4 Why do we care about the UV B dosage? Cholesterol photolysis to Vitamin D h →

Copyright © 2013 R. R. Dickerson & Z.Q. Li 5 Folate (vitamin B-9)

Copyright © 2013 R. R. Dickerson & Z.Q. Li 6 Too little UV radiation means rickets; UV converts cholesterol to Vitamin D. UVC to 290 nm UVB to 320 nm UVA to 400 nm

Copyright © 2013 R. R. Dickerson & Z.Q. Li 7 Too much UV radiation causes skin cancer and photodissociates folate, also called Vitamin B 9. Deficiency causes anemia and birth defects.

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Copyright © 2013 R. R. Dickerson & Z.Q. Li 11 The Stratospheric Ozone Layer Without a protective ozone layer there can be no protein-based life on the surface of the Earth. Here we examine the catalytic cycles that control the level of ozone in the stratosphere. We will calculate the O 3 abundances expected for various levels of understanding. 1)Chapman Reactions (1931) O 2 + hv 2O(1) O + O 2 + M O 3 + M*(2) O 3 + hv O 2 + O(3) O + O 3 2O 2 (4)

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From The Stratosphere 1981 R. D. Hudson Editor 16

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Copyright © 2013 R. R. Dickerson & Z.Q. Li 18 O/O 3 = j(O 3 )/(k 2 M O 2 )

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Copyright © 2013 R. R. Dickerson & Z.Q. Li 23 The second catalytic cycle speeds up Reaction 4, that is it effectively increases k ₄. 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 NO ₂. Often “NOx” is used as “odd nitrogen” which includes NO ₃, HNO ₃, 2 N ₂ O ₅, HONO, PAN and other species. This total of “odd nitrogen” is better called “NOy” or “total reactive nitrogen.” N ₂ and N ₂ O are unreactive. NO + O ₃ → NO ₂ + O ₂ O + NO ₂ → NO + O ₂ O + O ₃ → 2O ₂ 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.

Copyright © 2013 R. R. Dickerson & Z.Q. Li 24 4) Stolarski & Cicerone (1974); Wofsy & McElroy (1974) “ClOx” Cl + O ₃ → ClO + O ₂ ClO + O → Cl + O ₂ O + O ₃ → 2O ₂ 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 O ₃ level. The general for of a catalytic ozone destruction cycle is: X + O ₃ → XO + O ₂ XO + O → X + O ₂ O + O ₃ → 2O ₂ NET

Copyright © 2013 R. R. Dickerson & Z.Q. Li 25 The Stratospheric Ozone Layer

Copyright © 2013 R. R. Dickerson & Z.Q. Li 26 How did Farby and Buisson do? At 3000 Å (300 nm) 1/100 = I/Io = ln(-  cl)  300 = 9.5 atm -1 cm -1 -ln(0.01)/9.5 = atm cm (compare to 0.50) atm cm = 485 DU Correct for zenith angle of 27 o for Paris? (cos 27 o = 0.9 so  = 432 DU.) [O 3 ] = 0.6 cm 3 m -3 = 6x10 -7 Is that right? [O 3 ] for uniform mixing ratio = column content/scale height 5 mm/8x10 6 mm = 6.25 x 10 –7 = 625 ppb As Fabry said this is too much for surface air, and the ozone layer lies above.

Copyright © 2010 R. R. Dickerson & Z.Q. Li 27 Slides 27 on will be presented in AOSC621 in 2015.

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