5.9 Chemistry of the atmosphere

Unit Summary

This unit aligns with the AQA GCSE Trilogy Science specification and develops a clear understanding of how Earth’s atmosphere has changed over time, the processes that control its composition, and the impact of human activities on atmospheric chemistry. It builds upon prior learning about the Earth’s resources and environmental chemistry to explain how natural processes and human actions influence atmospheric gases, climate, and air quality.

Students begin by studying the evolution of the Earth’s atmosphere, learning how volcanic activity, the formation of oceans, and the emergence of photosynthesising organisms shaped the early atmosphere into the modern composition of nitrogen, oxygen, and trace gases. They examine evidence used by scientists to reconstruct these changes and consider why historical atmospheric data must be interpreted through indirect methods.

The unit then develops understanding of the greenhouse effect, distinguishing between the natural process that keeps Earth warm enough to support life and the enhanced greenhouse effect driven by increasing levels of carbon dioxide, methane, and water vapour. Students learn how human activities—such as combustion of fossil fuels, agriculture, and deforestation—alter greenhouse gas concentrations, and how these changes contribute to global climate change. They explore potential environmental consequences, including rising sea levels, extreme weather, loss of biodiversity, and threats to food and water security.

Further learning focuses on air pollution and atmospheric chemistry. Students examine the formation of pollutants such as carbon monoxide, sulphur dioxide, nitrogen oxides, and particulates from incomplete combustion and industrial processes. They investigate how these pollutants contribute to respiratory problems, acid rain, and smog, and how atmospheric reactions—such as the oxidation of sulphur dioxide or formation of ground-level ozone—affect air quality and human health. Methods of reducing emissions, including alternative fuels, catalytic converters, and improved industrial processes, are also explored.

Substantive knowledge developed in this unit includes:

The evolution of the Earth’s atmosphere from volcanic gases to its present composition.

The role of photosynthesis and carbon cycling in regulating atmospheric gases.

The greenhouse effect and the distinction between natural and enhanced warming.

The sources, formation, and impacts of atmospheric pollutants.

The links between combustion processes, human activity, and climate change.

Strategies for reducing emissions and mitigating environmental impacts.

Disciplinary knowledge is strengthened through scientific enquiry and data interpretation. Students analyse graphs and datasets showing changes in atmospheric composition over time, interpret emissions statistics, evaluate claims about climate change, and explain scientific uncertainties in atmospheric modelling. Practical experiences may include small-scale investigations of combustion, examination of particulate filters, or modelling the greenhouse effect using infrared-absorbing materials. These activities support accurate observation, data handling, and explanation of evidence using scientific principles.

Assessment for Learning (AfL) is embedded throughout the unit using retrieval practice on atmospheric composition, diagnostic questions targeting common misconceptions (such as confusing the greenhouse effect with ozone depletion), and scaffolded writing tasks to support extended explanations of processes such as global warming or sulphur dioxide formation.

Real-world links underpin the unit, highlighting the relevance of atmospheric chemistry to global challenges including climate change, air pollution, renewable energy, and sustainability. Students engage with contexts such as carbon footprints, international climate agreements, and the science behind reducing emissions in transport and industry.

Designed to be accessible and conceptually coherent, this unit equips learners with the ability to describe and explain atmospheric processes, evaluate human impacts on the environment, and interpret evidence related to climate and air quality. By the end of the unit, students will be able to explain how the atmosphere has evolved, how pollutants are formed and controlled, and why atmospheric chemistry is central to understanding and addressing modern environmental issues.