Atmospheric Physics and Chemistry

Study Materials

Some Interesting Questions to Ponder

The purpose of these questions are to stimulate some thought - while the answers will be developed as part of the course you should at least begin to think about possible answers. To gain a sense of what you have learnt during the course on the first day of classes write down your best guess as to what the answers might be. At the end of the course revisit the questions once again, you should be able to give quantitatively correct answers to all the problems.

Puzzles in Atmospheric Science

1. Ozone (O₃) in the troposphere, where we live, is considered to be ‘bad’, but ozone in the stratosphere is ‘good’ - why?
2. If you use ideal gas laws it is easy to show that both the temperature and pressure of the atmosphere should decrease with height above the ground. In the stratosphere however, there are regions where the temperature increases with elevation - why?
3. Why don’t air molecules escape into space?
4. At noon the overhead sky is typically blue but at sunset, looking toward the horizon, the color is usually red, why?
5. How far can you see in a horizontal direction in clear air - what limits our ability to see distant objects?
6. If clouds are composed of liquid water droplets why do they stay aloft for such long times, and why do fogs form at the ground?
7. In the troposphere the two key reactions responsible for ozone (O₃) formation are
   • NO₂+ hν →NO + O (³P)
   • O (³P) + O₂+ M →O₃+ M
8. But if the only source of ozone is photoxidation of nitrogen dioxide (NO₂) and most of the emissions of NO_x= (NO + NO₂) are in the form of nitric oxide (NO) what role, if any, is played by emissions of Volatile Organics Compounds (VOC’s).
9. In terms of concentration, the primary species in the atmosphere are N₂, O₂and Ar. They are not greenhouse gases. Molecules like H₂O, CO₂, N₂O, and CFC’s, that only occur in trace amounts, are radiatively active - why?
10. Manufacturers of chlorine based disinfectants that are used in swimming pools often suggest that their products should be added at night rather than during the day - why?
11. In some undergraduate courses in mechanics you learn that fluid flows are often in the same direction as the pressure gradient. In the atmosphere there are situations where the flow is normal to the pressure gradient - why?
12. Air and water have very different heat capacities. What would be the equivalent depth of water, distributed over the globe that has the same total heat capacity as the atmosphere?
13. Carbon dioxide (CO₂) is an important climatically active gas, what is its atmospheric life time and, given the time scale for its removal, what are the implications for controlling global warming?
14. What is the mass of the atmosphere?
15. When you see white plumes being emitted from smoke stacks, is what you see air pollution, and if so what is its chemical composition?
16. Methanol (CH₃OH), derived from oil and gas, and ethanol (C₂H₅OH) from the fermentation of biomass, have been used either on their own as fuels or as additives to gasoline. Which one of the two alcohols would you choose as a fuel additive to lower air pollution in urban areas and why?
17. Why is it easier to get sun burnt at the top of a mountain and much less so in urban areas at sea level?
18. What causes the ‘brown haze’ over polluted areas? (Hint, it is not nitrogen dioxide NO₂.)
19. If you take a deep breath what is the likelihood that a nitrogen molecule now in your lungs was at one time also in the lungs of Albert Einstein?
20. The term ‘Green house effect’ frequently occurs in discussions about global climate, is this the right analogy to use when explaining atmospheric warming?
21. In the atmosphere two of the most important species responsible for the formation of photochemical oxidants, that cause health and welfare impacts, are the hydroxyl radical (OH) and the hydroperoxy radical (HO₂), but they are not regulated by pollution control agencies - why not?