The following are changes that affect the composition of our atmosphere.

1. Human activities such as the combustion of fossil fuels, has increased the levels of greenhouse gases.
2. At dew point, the water vapor begins to condense out of air.
3. Human activities, such as the combustion of fossil fuels, generate the aerosols.
4. You observe hail when the temperatures are below the freezing point.
5. Carbon dioxide is produced during respiration of plants, animals, fungi, and microorganisms.

Which of these phenomena involve physical changes and which involve chemical reactions?