1. Environmental Chemistry

2. Stratospheric Chemistry
The Ozone Layer - Shield against dangerous incoming radiation
How does radiation interact with molecules in the stratosphere?
What processes form and maintain the ozone layer?
How much ozone is there, and how is it distributed? How do we know?
How have human activities altered ozone chemistry and the ozone layer itself?
What controls have been put in place to protect the ozone layer?
Ozone is a “success story” in environmental chemistry – what lessons can we learn from it?
The stratosphere is also a good “case study” in how atmospheric chemistry works

3. Ozone layer characteristics

4. Global ozone
Ozone column – total amount of ozone between ground and top of atmosphere
Dobson Unit – an amount of ozone equivalent to a mm thick layer of ozone when brought to ground level
300 DU = 3 mm ozone colum

5. How is ozone measured?

6. Ozone Update NASA OzoneWatch: http://ozonewatch.gsfc.nasa.gov/
NOAA ESRL Global Monitoring Division Webpage:

7. Air circulation in the stratosphere
Air enters the stratosphere through the tropopause in the tropics
T is very low (200 K), so air in strat is DRY (~ 5 ppmv H2O)
T increases with alt so air is stratified – no vertical motion
Air stays in stratosphere for ~5 yrs before returning to troposphere

8. Solar spectrum

10. O2 Absorption Spectrum Graedel and Crutzen, Atmospheric Change, 1993
Schumann-Runge continuum
ionization continuum
Herzberg continuum
Schumann-Runge bands
Graedel and Crutzen, Atmospheric Change, 1993

11. Ozone UV absorption spectrum
Graedel and Crutzen, Atmospheric Change, 1993

12. Actinic Flux O2 O3

13. Comparing to observations
Ozone concentrations are lower than predicted based on oxygen-only chemistry

15. Global ozone
Ozone column – total amount of ozone between ground and top of atmosphere
Dobson Unit – an amount of ozone equivalent to a mm thick layer of ozone when brought to ground level
300 DU = 3 mm ozone colum

16. Catalysis of ozone chemistry
Radicals lower the reaction barrier so reaction goes faster

17. Calculating rates of reactions

18. Ox production and loss rates
(24-hour averages)
Jacob, Intro. to Atmospheric Chemistry, 1999.

19. O3 loss rates without and with heterogeneous chemistry
With heterogeneous reactions
Jacob, Intro. to Atmospheric Chemistry, 1999.

20. Ozone column trend, 60oS-60oN
% Change
Pinatubo
Year

21. Midlatitude ozone trend vs. altitude
Jacob, Intro. to Atmospheric Chemistry, 1999.

22. https://www. researchgate

24. The ozone hole
At its peak on Sept. 28, 2016, the ozone hole extended across an area nearly three times the size of the continental United States. The purple and blue colors are where there is the least ozone, and the yellows and reds are where there is more ozone. Credit: NASA's Goddard Space Flight Center

25. The ozone hole

26. Ozone Update NASA OzoneWatch: http://ozonewatch.gsfc.nasa.gov/
NOAA ESRL Global Monitoring Division Webpage:

27. Projected atmospheric chlorine levels without the Montreal Protocol
WMO, Scientific Assessment of Stratospheric Ozone: 2002.

28. CFCs today