Across
- 2. the change in average weather
- 3. lung system
- 6. tiny solid or liquid particles such as dirt dust soot and/or smoke
- 7. the release of substances from natural sources into the air
- 8. naturel resources such as coal, oil, and natural gases
Down
- 1. building used to test air quality
- 2. the most important gas released by human activities
- 4. when an engine is running but the vehicle is not moving
- 5. breathing decease of the lungs
- 6. extremely small atom