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Ozone Depletion

Ozone Depletion. O 3. Ozone Factoids. Good in the stratosphere, bad in the troposphere Produced at a height of ~50 km, settles to a height of 23 km Filters out 95 – 99% of incoming UV-A and UV-B ( 0.2 m - 0.3 m ; m = 10 -6 m )

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Ozone Depletion

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  1. Ozone Depletion O3

  2. Ozone Factoids • Good in the stratosphere, bad in the troposphere • Produced at a height of ~50 km, settles to a height of 23 km • Filters out 95 – 99% of incoming UV-A and UV-B (0.2m - 0.3m; m= 10-6m) • Formation may be the mechanism that explains the warming trend in the stratosphere • O3 depletion is a global problem

  3. O3 Chemistry – Formation of Ozone • O2 O. + O.(O. = free radical, very reactive) • O. + O2 + M + UV  O3 + M + IR • O. + O. + M  O2 + M • (M = a non reactive body that absorbs the energy)

  4. Reasons for Depletion • Freons (CFCs) – 1 freon molecule can destroy 100,000 O3 molecules • Methyl bromide (CH3Br) - fumigant • Halons – used in fire extinguishers • High flying jets (NOx)

  5. OZONE DEPLETION IN THE STRATOSPHERE One CFC molecule can destroy 100,000 ozone molecules

  6. How is Ozone Measured? • What is a Dobson Unit? • A dobson unit is the most basic measure used in ozone research. The unit is named after G.M.B. Dobson, one of the first scientists to investigate atmospheric ozone (~1920 - 1960). He designed the 'Dobson Spectrometer' - the standard instrument used to measure ozone from the ground. The Dobson spectrometer measures the intensity of solar UV radiation at four wavelengths, two of which are absorbed by ozone and two of which are not.

  7. Dobson Unit • The illustration below shows a column of air, 10 deg x 5 deg, over Labrador, Canada. The amount of ozone in this column (i.e. covering the 10 x 5 deg area) is conveniently measured in Dobson Units. • If all the ozone in this column were to be compressed to STP (0oC and 1 atmosphere pressure) and spread out evenly over the area, it would form a slab approximately 3mm thick. • 1 Dobson Unit (DU) is defined to be 0.01 mm thickness at STP; the ozone layer over Labrador then is ~300 DU.

  8. Ozone Depletion • Size of ozone hole

  9. Impacts • Increases in rates of skin cancer (1% decline in O3 layer  4 – 5% increase in skin cancer) • Cataracts • Impaired immune systems • Decline in phytoplankton population

  10. Solutions • Ban CFCs • Find replacements for HFCs • Ban halons • Ban methyl bromide

  11. Global Agreements • 1987  Montreal Protocol • 1992  Copenhagen Agreements

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