Chemistry of the atmosphere

• The early atmosphere came from volcanic activity — its CO₂ steam-cooled to the oceans; photosynthesis 光合作用 (algae, plants) raised oxygen and buried carbon.
• Greenhouse gases — CO₂ and methane — trap radiation; human activity raises them and the global climate change 全球气候变化s.
• Pollutants from fuels — CO, SO₂, NOₓ, particulates 颗粒物 — each with a source, a chemistry and a consequence.

Theories: the early atmosphere cannot be known for certain — evidence comes from gases trapped in ancient ice and from other planets' atmospheres today. Intense volcanic activity released gases: mostly carbon dioxide, with water vapour, nitrogen and traces of methane and ammonia — little or no oxygen.

The water vapour condensed to form the oceans; CO₂ dissolved in them and was locked into carbonate sediments (shells). Over ~2.7 billion years, algae and plants photosynthesised, absorbing CO₂ and releasing oxygen — oxygen rose, CO₂ fell; much carbon was buried as fossil fuel 化石燃料s. Nitrogen, unreactive, accumulated to dominate today's air: about four-fifths N₂, one-fifth O₂, plus argon and ~0.04 % CO₂.

Greenhouse gases 温室气体 — carbon dioxide, methane and water vapour — absorb and re-emit some of the long-wavelength infrared radiation that the warm Earth radiates to space, keeping the surface warmer than it would otherwise be. The global climate change hypothesis says rising greenhouse-gas levels raise the average temperature.

Human causes: deforestation (less CO₂ absorbed), burning fossil fuels (more CO₂), cattle/rice and landfill (methane). Consequences discussed in the spec: melting ice, sea-level rise, changing rainfall and extreme weather. The scientific consensus rests on peer-reviewed evidence — interpret given data on temperature, CO₂ and methane over time.

Combustion of fuels releases:

• carbon monoxide (CO) — a toxic gas from incomplete combustion 不完全燃烧 in limited oxygen; binds haemoglobin, reducing oxygen transport;
• carbon particulates (soot) — also from incomplete combustion; worsen respiratory problems and cause global dimming;
• sulfur dioxide (SO₂) and oxides of nitrogen (NOₓ) — from impurities in fuel / nitrogen reacting at engine temperatures; cause acid rain 酸雨 (damaging trees, lakes, buildings) — removed from flue gases by neutralisation with alkalis (e.g. calcium oxide);
• NOₓ also forms at high engine temperatures from N₂ + O₂, and contributes to photochemical smog.

Complete combustion — plenty of oxygen — gives CO₂ and water only.

• The evolution sequence with the evidence and its uncertainty; today's composition in fractions.
• Greenhouse mechanism in terms of wavelength; the four human causes; consensus and data interpretation.
• Each pollutant: source, complete vs incomplete combustion, effect, and one mitigation.