1. What’s coming up??? Oct 25The atmosphere, part 1Ch. 8 Oct 27Midterm … No lecture Oct 29The atmosphere, part 2Ch. 8 Nov 1Light, blackbodies, BohrCh. 9 Nov 3Postulates of QM, p-in-a-boxCh. 9 Nov 5,8Hydrogen atomCh. 9 Nov 10,12Multi-electron atomsCh.10 Nov 15Periodic propertiesCh. 10 Nov 17Periodic propertiesCh. 10 Nov 19Valence-bond; Lewis structuresCh. 11 Nov 22Hybrid orbitals; VSEPRCh. 11, 12 Nov 24VSEPRCh. 12 Nov 26MO theoryCh. 12 Nov 29MO theoryCh. 12 Dec 1Putting it all together Dec 2Review for exam

2. The atmosphere Made up of a mixture of gases (mainly N 2 and O 2 ) Mole fractions of major gases (nitrogen, oxygen, carbon dioxide, argon) are pretty constant with altitude “interesting stuff” involves tiny amounts of trace gases – ozone, oxides of nitrogen and sulfur and some others

3. ~ 100%

5. Breathing!!!

6. Argon, Neon, Xenon … rare gases often used in “neon” lights

7. Atmospheric gases can be separated by distillation, since they have different boiling points N 2 77 K O 2 90 K Ar87 K Ne24 K CH 4 111 K

9. Pressure profile of atmosphere Pressure drops almost exponentially with increasing altitude... why?? Trop. Strat.

10. Temperature profile in the atmosphere stratosphere

11. pV = nRTideal gas law is “pretty good” (why??) Sun warms Earth’s surface … p is constant, so (n / V) decreases … p = (n/V) RT T goes up p stays constant Therefore, density goes down

12. Warmer, less dense air rises and expands … work done against the surroundings … … internal energy is lost …. Therefore the air parcel cools

13. Temperature profile in the atmosphere stratosphere

14. The warming that happens through the stratosphere is due to chemical reactions which release heat … exothermic These reactions involve ozone chemistry: O 2 + UV light  O + O heat released O + O 2 + M  O 3 + M heat released ( M is required to remove excess energy) O + O 3  2 O 2 heat released O 3 + UV light  O 2 + O heat released

15. Outer space Cooling again Heating due to Ionic reactions

16. Aurora borealis: Northern lights are actually due to ions in the ionosphere reacting with charged particles from the solar wind

17. Equilibrium vapour pressure of water Relative humidity > 100% water condenses Relative humidity < 100% water evaporates

19. High altitude clouds (like cirrus clouds) are generally made of ice crystals Lower clouds (rain clouds!) are composed of liquid water droplets

21. Ozone in the atmosphere Most of the atmospheric ozone is in the stratosphere, in the “ozone layer”

22. Basic ozone chemistry: O 2 + UV light  O + O heat released O + O 2 + M  O 3 + M heat released ( M is required to remove excess energy) O + O 3  2 O 2 heat released O 3 + UV light  O 2 + O heat released The ozone layer exists because of a balance between formation and destruction reactions

23.  H 0 f (O 2 ) = ….  H 0 f (O 3 ) = 142.7 kJ/mol  H 0 rxn = 2  H 0 f (O 3 )  3  H 0 f (O 2 ) =  285.4 kJ/mol

24. O 3 + UV light  O 2 + O Ozone absorbs dangerous wavelengths of solar radiation in the stratosphere (where the ozone concentration is high) before it can reach the surface of the earth

26. Almost entirely from humans! These help to destroy ozone in the stratosphere

27. These chemical cycles are faster than the reactions which only involve oxygen species. They are most important in the Antarctic (and sometimes the Arctic) regions of the stratosphere, during the local springtime (late Sept-Nov in Antarctica)

28. Early spring Depleted ozone correlates with increased ClO

29. Ozone “hole”

31. The decrease in ozone concentration in the stratosphere has resulted in an increase of the UV light which is no longer absorbed there Toronto

32. Up-to-the-minute newsbreak! What’s up with this year’s ozone hole? Go to http://jwocky.gsfc.nasa.gov/