GCSE / Chemistry
Chemistry of the Atmosphere
Learn the composition and evolution of the Earth’s atmosphere, greenhouse gases, climate change, carbon footprints and atmospheric pollutants for GCSE Chemistry. This topic covers how oxygen increased, why carbon dioxide decreased, the greenhouse effect, human impacts on the atmosphere, combustion pollutants and their environmental effects.
The modern Earth’s atmosphere has remained fairly stable for about 200 million years and contains approximately 80% nitrogen, 20% oxygen and small proportions of gases including carbon dioxide, water vapour and noble gases.
Evidence about the Earth’s early atmosphere is limited because the planet formed about 4.6 billion years ago, so scientists use geological evidence and models to develop and evaluate theories about how the atmosphere changed over time.
One theory suggests that intense volcanic activity during the first billion years released gases that formed the early atmosphere, which was probably rich in carbon dioxide with little or no oxygen, together with water vapour, nitrogen and small amounts of methane and ammonia.
As the Earth cooled, water vapour condensed to form the oceans; carbon dioxide dissolved in seawater and became incorporated into carbonate sediments, helping to reduce the concentration of carbon dioxide in the atmosphere.
Algae and plants gradually increased atmospheric oxygen through photosynthesis, represented by in the presence of light.
Algae began producing significant oxygen billions of years ago, and as plants evolved the percentage of oxygen in the atmosphere increased until conditions could support more complex forms of animal life.
Atmospheric carbon dioxide decreased because it was removed by photosynthesis, dissolved in the oceans and became locked into sedimentary carbonate rocks such as limestone and carbon-containing fossil fuels such as coal, crude oil and natural gas.
Greenhouse gases including carbon dioxide, methane and water vapour absorb and re-emit infrared radiation from the Earth, helping maintain temperatures high enough for life; this process is known as the greenhouse effect.
Human activities can increase greenhouse gas concentrations; burning fossil fuels and deforestation increase atmospheric carbon dioxide, while livestock farming, landfill sites and some agricultural activities can increase methane emissions.
Many scientists conclude from peer-reviewed evidence that increasing greenhouse gas concentrations from human activity are contributing to increasing average global temperatures and global climate change, although predictions contain uncertainties because climate systems are complex.
Possible effects of global climate change include changes in rainfall patterns, more frequent or severe extreme weather, melting ice, rising sea levels, changes to habitats and ecosystems, and changes in the distribution of species.
A carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event; it can be reduced through lower fossil-fuel use, improved efficiency, renewable energy and reduced waste.
Burning fuels can release atmospheric pollutants including carbon monoxide, sulfur dioxide, oxides of nitrogen, particulates and unburned hydrocarbons, depending on the fuel composition and the conditions under which combustion occurs.
Carbon monoxide is a toxic, colourless and odourless gas produced by incomplete combustion; sulfur dioxide and nitrogen oxides can cause respiratory problems and contribute to acid rain, while particulates can damage health and cause global dimming.