The evolution of the atmosphere and the present composition, greenhouse gases and climate change, atmospheric pollutants from fuels, and using the Earth's resources sustainably including potable water and recycling.

What this topic is asking

AQA wants you to describe how the atmosphere evolved and its present composition, explain greenhouse gases and climate change, describe atmospheric pollutants from fuels, and explain how the Earth's resources are used sustainably including making potable water.

The evolving atmosphere

For about 200 million years the proportions of gases have been roughly steady. Today's atmosphere is about 80% (four fifths) nitrogen, 20% (one fifth) oxygen, with small amounts of carbon dioxide (about 0.04%), water vapour and noble gases such as argon. The increase in oxygen and the locking-away of carbon dioxide were essential for animals to evolve. Carbon dioxide was removed in three main ways: dissolving in the oceans, being used in photosynthesis by algae and plants, and being locked into sedimentary rocks (such as limestone) and into fossil fuels (coal, crude oil and natural gas) formed from the remains of organisms.

Greenhouse gases, climate change and pollutants

The consequences of climate change include rising sea levels from melting ice and thermal expansion, more frequent and severe storms, changes to rainfall patterns and the distribution of species, and reduced biodiversity. Because the climate system is complex and the data are hard to model, scientists work with peer-reviewed evidence, and the level of confidence in the link between human carbon dioxide emissions and warming is now very high. A product's carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over its whole life, from raw materials to disposal; it can be reduced by using renewable energy, improving efficiency, and capturing and storing carbon dioxide.

Burning fuels can also produce pollutants, especially when combustion is incomplete or the fuel contains impurities:

• Carbon monoxide (from incomplete combustion when oxygen is limited): a toxic, colourless, odourless gas that binds to haemoglobin so the blood carries less oxygen.
• Sulfur dioxide and oxides of nitrogen (from sulfur impurities and from nitrogen reacting at the high temperatures inside engines): cause acid rain, which damages buildings and ecosystems, and cause respiratory problems.
• Particulates (unburnt carbon, soot): cause global dimming (reflecting sunlight) and health problems such as lung damage.

Using resources sustainably

The Earth's resources are finite, so we must use them sustainably to leave enough for future generations. Chemistry helps by improving processes and developing alternatives, but the priority order is reduce, reuse and recycle: using fewer raw materials, reusing products, and recycling materials such as metals, glass and plastics, all of which save energy, raw materials and reduce waste. A life cycle assessment (LCA) weighs the environmental impact of a product at each stage (extracting and processing raw materials, manufacturing, use, and disposal), helping to compare options such as a paper bag against a plastic bag.