Useful introductory material for "atmospheric chemistry" and "air pollution"

Wikipedia "Atmospheric Chemistry"

Review Questions
1. Express the percentage of nitrogen in the atmosphere (78.084%) as a mixing ratio in parts per million?
2. Is the percentage of nitrogen in the atmosphere, when expressed as 78.084%, a true mixing ratio that one would observe, or the 'dry mixing ratio'?
3. Why is the CO₂ mixing ratio expressed both as 400 ppm and 370 ppm in the Wikipedia page?
4. What is the most recent year in history when the CO₂ mixing ratio was last equal to 370 ppm (as measured at Mauna Loa, Hawaii)?
5. Before 1900, when was the CO₂ mixing ratio last above 350 ppm?
6. What is the typical mixing ratio of water vapor?
7. If you were to take a real air parcel and measure water vapor, how likely is it that you would measure this "typical" mixing ratio?

Hot topics in Atmospheric Chemistry
New Legislative Package Announced to Protect Californians from Air Pollution (January 11, 2016 - NRDC website)