Air Quality and Climate

Clean dry air is about 78% nitrogen, 21% oxygen, 0.9% argon and 0.04% carbon dioxide. Pollutants include carbon monoxide (incomplete combustion; toxic), sulfur dioxide (burning sulfur in fossil fuels; acid rain), oxides of nitrogen (car engines; acid rain, smog), particulates (lung damage). Carbon dioxide and methane are greenhouse gases: they absorb infrared radiation, causing global warming and climate change. Catalytic converters, flue-gas desulfurisation and renewable energy reduce emissions.

Cambridge 5070 Paper 1Cambridge 5070 Paper 2Cambridge 0620 Papers 2, 4Cambridge 0620 Papers 1, 3Edexcel 4CH1 Paper 1CEdexcel 4CH1 Paper 2C≈ 40 minRevision 1 · updated 2026-10-30

Section 1 of 14

Learning objectives

State the composition of clean air.
Describe the sources, effects and reduction of common pollutants.
Explain the greenhouse effect and ways to reduce climate change.

Pause and think

Car engines don't put any nitrogen in their fuel, so why do they produce nitrogen oxides?

Section 2 of 14

Core idea

Start hereEvery breath

You breathe about 11,000 litres of air a day. In a busy city, that air may carry soot, nitrogen dioxide and carbon monoxide, each from a different source and each doing different harm.

The big idea

Clean air is mainly nitrogen and oxygen. Burning fuels adds pollutants that cause acid rain and health problems, and greenhouse gases that warm the planet.

1. Pollutants

Sources and effects

Drawing diagram…

Most pollutants come from burning fuels.

Worked exampleMeasuring oxygen in air

$100\ \mathrm{cm^3}$ of air is passed repeatedly over hot copper. The volume falls to $79\ \mathrm{cm^3}$ .

Goal: % oxygen.
Strategy: Copper removes oxygen as copper(II) oxide.

$100-79=21\ \mathrm{cm^3}$
Volume of oxygen removed.
$\frac{21}{100}\times100=21\%$
Percentage.

Answer

21\%

oxygen.

✓ CheckMatches the known value ✓.

2. Climate change

Sunlight warms the Earth's surface, which emits infrared radiation. Greenhouse gases absorb some of it and re-emit it in all directions, including back to the surface. More $\mathrm{CO_2}$ and $\mathrm{CH_4}$ means more heat trapped, raising average temperatures and changing climate patterns.

Exam tipReducing emissions Renewable energy, energy efficiency, planting trees, reducing meat and dairy consumption, and capturing landfill methane.

Pause and think

Why are catalytic converters good for air quality but not for climate?

Summary

Air: 78% N₂, 21% O₂.
Pollutants: source, effect, fix.
Greenhouse gases trap infrared.

Acid rain: Rain made acidic by dissolved sulfur dioxide and nitrogen oxides.
Greenhouse gas: A gas that absorbs infrared radiation.
Catalytic converter: Device that converts CO and NOx into less harmful gases.

HistoryThe Great Smog. In December 1952, a smog of coal smoke and sulfur dioxide covered London for five days and caused around 12,000 deaths, leading to the UK's Clean Air Act of 1956.

Fun factKeeling Curve. Since 1958,

\mathrm{CO_2}

has been measured on top of Mauna Loa in Hawaii. The record zigzags every year as northern forests grow and shed leaves, while the long-term rise continues.

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