1. METO 621 Lesson 23

2. The Ozone Hole

3. Decline in mean October ozone levels over Halley Bay

4. Ozone concentrations over Syowa Station

5. Schematic of the winter polar vortex

6. Ozone Hole

7. ClO and O 3 in mid-September

8. Partitioning of Chlorine

9. Polar Stratospheric Clouds There are two main classes of PSC. Type 1 PSC are small (<1  m) HNO 3 rich particles. These have a mass mixing ratio of about 10 ppbm. Type II PSC are larger (from 10  m to about 1 mm) composed primarily of H 2 O-ice with minor amounts of HNO 3 as hydrates. They can constitute up to 1000 ppbm of the stratosphere. As noted before, the primary reaction that can be induced on the surface of the PSC is ClONO 2 + HCl → Cl 2 + HNO 3 The HNO 3 is then retained in the PSC.

10. Polar Stratospheric Clouds The overall catalytic cycle is 2(Cl+O 3 → ClO + O 2 ) ClO + ClO + M → (ClO) 2 + M (ClO) 2 + h → Cl + ClOO ClOO + M → Cl + O 2 + M net 2O 3 → 3O 2

11. Overall chemistry within the vortex

12. Ozone loss within the Arctic Vortex

13. Temperature and chlorine monoxide in the Arctic

14. Total Ozone Field March 11, 1990 Nimbus 7 TOMS (Hudson et al., 2003)

15. Latitudinal Average for Total Ozone March 11, 1990 (Hudson et al., 2003)

16. Total ozone with seasonal component removed LINEAR FITS Overall (black) 3.2% decade Polar (Blue) 2.5% per decade Mid-latitude (Green) 2.2 per decade Tropical (Red) 1.9% per decade Linear fit from Jan 1979 to May 1991

17. Total Mass of Ozone The difference between the overall and regime trends can be explained by looking at the equation for the total mass of ozone: M = AΩ 0 = A P Ω P + A M Ω M + A T Ω T +A A Ω A –A =total area between 25 and 60°N, and Ω 0 = overall mean column ozone –A P, A M, A T = regime areas Ω P, Ω M, Ω T = regime mean column ozone One can get a trend if the regime Ω varies with time, or the regime A varies with time, or both

18. Dynamics versus Chemistry