Chemistry does not happen in isolation from the world around us. The air we breathe, the water we drink, and the soil that grows our food are all chemical systems, and human activity is increasingly putting them under stress. Chapter 10 steps back from the laboratory and looks at chemistry in the context of the environment, examining both the natural chemistry of our planet and the ways in which we are disrupting it.

We begin with water, looking at how its purity is tested, what substances are naturally present in water from the environment, and how the domestic water supply is treated to make it safe. We then move on to fertilisers, examining the role of nitrogen, phosphorus and potassium in plant growth and how NPK fertilisers are used to improve crop yields, alongside the environmental problems that arise from their overuse.

The bulk of the chapter is devoted to air quality and climate. We examine the composition of clean dry air, before looking at the sources and adverse effects of a range of air pollutants, including carbon dioxide, carbon monoxide, methane, oxides of nitrogen, sulfur dioxide and particulates. We discuss the mechanisms by which greenhouse gases contribute to global warming, how oxides of nitrogen form in car engines and are removed by catalytic converters, and what strategies can be employed to reduce the impact of climate change and acid rain. The chapter closes with photosynthesis, which serves as a reminder that the natural world has its own chemistry, quietly working to maintain the balance that human activity continues to disturb.