Capstone: Sort the Gases
One distinction runs through the whole topic and earns marks everywhere: a greenhouse gas warms the planet; an atmospheric pollutant is something not in clean air that causes problems near the ground; and the two main gases of clean air are neither. Sort all nine to check you can keep them apart.
Drag each gas into a box — or tap it to step through the boxes. Then press Check.
- Today’s atmosphere — about 80% nitrogen and 20% oxygen, with small amounts of carbon dioxide, water vapour and noble gases; roughly constant for the last 200 million years.
- The early atmosphere — formed by intense volcanic activity: mainly CO2 with water vapour and little or no oxygen (like Mars and Venus). As the Earth cooled, water vapour condensed to form the oceans, CO2 dissolved and carbonates precipitated. Evidence is limited because it was ~4.6 billion years ago.
- Oxygen up, carbon dioxide down — algae (then plants) added oxygen by photosynthesis from ~2.7 bya (6CO2 + 6H2O → C6H12O6 + 6O2); CO2 was removed and locked into oceans, sedimentary rocks (limestone) and fossil fuels.
- The greenhouse effect — water vapour, CO2 and methane. Short-wavelength radiation in → absorbed by the surface → re-emitted as long-wavelength (infrared) → greenhouse gases absorb and re-radiate it (not “reflect”), trapping heat.
- Human activity & climate change — CO2 from burning fossil fuels and deforestation; methane from livestock, rice fields and landfill. CO2 correlates with temperature (peer-reviewed evidence). Four effects: rising sea levels, more severe storms, droughts/floods, changes to habitats and species. A correlation does not prove cause.
- The carbon footprint — the total CO2 and other greenhouse gases over the full life cycle of a product, service or event; reduce it with renewables, efficiency, public transport/EVs and carbon capture — limited by cost, developing technology, economics/politics and lifestyle.
- Pollutants from fuels — complete combustion → CO2 + water; incomplete (too little oxygen) → carbon monoxide + soot; sulfur in the fuel → SO2; the high temperature of engines makes nitrogen and oxygen from the air react → oxides of nitrogen.
- Effects of pollutants — CO is toxic, colourless and odourless (binds haemoglobin, so blood carries less oxygen); SO2 and NOx cause acid rain and respiratory problems; particulates cause global dimming and health problems.
That is the arc of C9: a planet that built its own breathable atmosphere over billions of years, a delicate greenhouse balance that keeps it warm enough for life, and the pollutants and extra greenhouse gases that burning fuels now adds. For Paper 2 it sits between C8 Chemical Analysis (the tests that identify gases such as carbon dioxide) and C10 Using Resources (how we respond) — and the combustion chemistry here links straight back to C7 Organic Chemistry, the fuels themselves.