| A | B |
|---|
| weather | the condition of the Earth's atmosphere at a particular time and place |
| ozone | the molecule made of three oxygen molecules |
| aneroid barometer | a barometer that does not use any liquid |
| oxygen | there is less of this per cubic meter at the top of a mountain |
| air pollutants | harmful particles and gases in the air |
| water | Acid rain can form when this mixes with sulfur oxides to form sulfiric acid |
| greenhouse effect | the natural process of Earth trapping some of the Earth's energy and using it to heat the lower atmosphere |
| atmosphere | the thin layer of gases that surrounds the Earth |
| 21% | dry air is made of this much oxygen |
| density | as altitude increases, this decreases |
| troposphere | the lowest level of the atmosphere where people live |
| smog | nitrogen oxides react with other air pollutants in the presence of sunlight to form this |
