The composition of clean air
Clean, dry air is about 78% nitrogen, 21% oxygen, roughly 1% argon (a noble gas), and about 0.04% carbon dioxide, plus small amounts of water vapour.
Key idea
Air pollutants come mainly from burning fuels: carbon monoxide (CO) from incomplete combustion (toxic), sulfur dioxide (SO2) from sulfur in fuels (acid rain), and oxides of nitrogen (NO/NO2) formed in hot engines (acid rain and smog).
Greenhouse gases and climate
Carbon dioxide and methane are greenhouse gases. They trap heat radiated from the Earth. Rising levels increase the greenhouse effect, causing global warming and climate change.
Reducing pollution
Catalytic converters in cars change harmful gases into safer ones:
Worked example
In a catalytic converter, carbon monoxide and nitrogen monoxide react: 2CO + 2NO → 2CO2 + N2. Check: 2 C, 2 N and 2 + 2 = 4 O on each side — the equation is balanced. Both harmful gases become less harmful carbon dioxide and nitrogen.
Remember
- Air: 78% N2, 21% O2.
- CO is toxic (binds to haemoglobin); SO2 and NOx cause acid rain.
- CO2 and CH4 are the main greenhouse gases.