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Combined Science Chemistry

Chemistry study notes

Maintaining Air Quality

Connect atmospheric substances to their sources, effects and possible solutions.

O-Level 5086 / 5088 (2026) / SEC G3 K326 / K328 (2027)

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3 topics

  1. What is in air, and where do pollutants come from?

    Separate the normal mixture from substances causing harm.

  2. Explain harm through a chemical cause

    Link the pollutant to the process and then the effect.

  3. Carbon cycling and greenhouse gases

    Track the flows before judging whether they balance.

Scope and references

Learning outcomes and sources

12. Maintaining Air Quality (5086 / 5088 / K326 / K328). Use the outcome map to find the explanation for a particular syllabus requirement.

See the learning outcome map

  1. 12(a) Describe dry-air composition

    • 78% nitrogen
    • 21% oxygen
    • Remainder noble gases, mainly argon, and CO2

    What is in air, and where do pollutants come from?

  2. 12(b) Name atmospheric pollutants

    • CO, CH4, NO, NO2, O3, SO2, unburned hydrocarbons

    What is in air, and where do pollutants come from?

  3. 12(c) Identify pollutant sources

    • CO from incomplete carbon-fuel combustion
    • NOx from lightning and engines
    • SO2 from volcanoes and fossil fuels

    What is in air, and where do pollutants come from?

  4. 12(d) Explain pollutant effects

    • CO toxicity
    • NO2/SO2 acid rain
    • Respiration and buildings

    Explain harm through a chemical cause

  5. 12(e) Explain the carbon cycle

    • Photosynthesis
    • Respiration
    • Combustion
    • Regulation of atmospheric CO2

    Carbon cycling and greenhouse gases

  6. 12(f) Explain greenhouse-gas effects

    • CO2 and CH4 sources
    • Global warming
    • Extreme weather and melting polar ice

    Carbon cycling and greenhouse gases