IP Chemistry Upper Sec 12: Maintaining Air Quality

These notes align with SEAB GCE O-Level Chemistry (6092) content used in IP programmes (exams from 2026).

Status: SEAB O-Level Chemistry 6092 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.

What you must know

• Dry air composition: ~78% nitrogen, 21% oxygen, ~1% argon, ~0.04% carbon dioxide.
• Pollutants and sources: carbon monoxide (incomplete combustion), sulfur dioxide (burning sulfur fuels/volcanoes), nitrogen oxides (vehicle engines/lightning), unburnt hydrocarbons (engines), methane (decomposition, agriculture), ozone (secondary pollutant).
• Effects: CO is toxic (binds haemoglobin), SO₂/NOₓ → acid rain damaging lungs/buildings/aquatic life, particulates worsen respiratory issues, tropospheric ozone irritates lungs; greenhouse gases trap heat.
• Controls: catalytic converters (oxidise CO/HC, reduce NOₓ), limestone/calcium carbonate to neutralise acidic gases (flue gas desulfurisation), low-sulfur fuels, better combustion/engine tuning.
• Carbon cycle: photosynthesis removes $\ce{CO2}$; respiration/combustion release it; deforestation + fossil fuel use increase atmospheric $\ce{CO2}$