Chemistry of the Atmosphere

This unit covers the evolution of Earth's atmosphere, the greenhouse effect, climate change, atmospheric pollutants and their sources and effects.

It is a shorter unit and largely descriptive, but it rewards precision. The early atmosphere questions expect the sequence of changes and the reasons for each, particularly the role of photosynthesis in increasing oxygen and reducing carbon dioxide. Greenhouse gas questions need the mechanism, not just the name: gases absorb long-wavelength radiation reflected from the Earth and re-emit it. Pollutant questions expect the source and the effect together — sulfur dioxide comes from sulfur impurities in fuels and causes acid rain. Students lose marks by giving vague environmental statements rather than named gases with named consequences. Evaluating evidence about climate change appears regularly.