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Urban transport and air pollution

Edexcel IAL Geography · WGE02 Geographical Investigations

As economies develop, vehicle numbers rise fast, and transport becomes a major source of urban air pollution, along with physical factors and other sources (spec 2.4.2, key idea 1). Study this through a local place context if you can.

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Rising vehicle numbers

Industrialisation, economic development and rising affluence increase motor vehicles rapidly: first motorbikes and scooters, then cars as incomes rise, and goods vehicles as trade grows. Cities often grow faster than road space or public transport, and many older vehicles in poorer cities lack modern emission controls.

Pollutants and their sources

WHO (fact sheet, October 2024):

Particulate matter (PM10, PM2.5): tiny particles from fuel combustion (especially diesel), brake and tyre wear, road dust, industry and domestic burning. PM2.5 penetrates deep into the lungs.
Nitrogen dioxide (NO2, part of NOx): from fuel combustion in transport and industry.
Low-level (ground-level) ozone: not emitted directly; formed when NOx and other gases react in sunlight, so it peaks on hot, sunny days.
Also carbon monoxide (incomplete combustion) and sulphur dioxide (coal and oil burning).

Other sources: domestic (cooking and heating with wood, coal, kerosene) and industrial (power stations, factories, construction dust). The June 2024 mark scheme credited sources visible in a photo (traffic, power lines suggesting electricity generation, factories) but not pollutant names such as CO2 when sources were asked for.

Physical factors

Physical geography can trap pollution:

Temperature inversions: a layer of warm air sits over cooler air near the ground, stopping pollutants rising and dispersing.
Relief: cities in basins or valleys, surrounded by mountains, trap still air.
Weather: calm, anticyclonic conditions with light winds let pollution build up; rain washes particles out.
Climate: strong sunshine increases ozone formation; dry seasons increase dust.

IQAir's 2024 World Air Quality Report (March 2025) found only 7 countries met the WHO annual PM2.5 guideline of 5 micrograms per cubic metre, and only 17% of cities. The most polluted city was Byrnihat, India, at 128.2.

Country	Annual mean PM2.5, 2024 (micrograms per m3)
Chad	91.8
Bangladesh	78.0
Pakistan	73.7
Democratic Republic of the Congo	58.2
India	50.6

Source: IQAir World Air Quality Report 2024

Worked example

Byrnihat's 2024 annual mean PM2.5 was 128.2 micrograms per cubic metre. How many times the WHO annual guideline of 5 is that?

128.2 / 5
= 25.64

Answer: About 25.6 times the guideline.

Key idea: Development and affluence increase vehicles. Transport emits PM, NOx and (via sunlight) ozone; domestic and industrial sources add more; inversions, basins and calm weather trap pollution. Only 7 countries met the WHO PM2.5 guideline in 2024.

Check yourself

India's 2024 annual mean PM2.5 was 50.6 micrograms per m3. How many times the WHO guideline of 5 is that? Give your answer to 1 decimal place.
Show answer
10.1 times. 50.6 / 5 = 10.12, so 10.1 times.
By how many micrograms per m3 was Chad's PM2.5 (91.8) higher than Bangladesh's (78.0) in 2024? Give your answer to 1 decimal place.
Show answer
13.8 micrograms per m3. 91.8 - 78.0 = 13.8.
Why do ground-level ozone levels usually peak on hot, sunny days?
- Cars emit more ozone when it is hot
- Rain is heavier in summer
- Ozone is released by the sea
- Ozone forms when NOx and other gases react in sunlight
Show answer
Ozone forms when NOx and other gases react in sunlight. It is a secondary pollutant formed photochemically.
A question asks you to identify a source of air pollution in a photograph. Which answer would gain credit?
- Heavy traffic on the road
- Carbon dioxide
- Particulate matter
- Nitrogen dioxide
Show answer
Heavy traffic on the road. The June 2024 mark scheme credited sources, not pollutant types.
A temperature inversion makes pollution worse because
- it creates strong winds
- it causes heavy rain
- a layer of warm air over cooler air stops pollutants rising and dispersing
- it lowers vehicle numbers
Show answer
a layer of warm air over cooler air stops pollutants rising and dispersing. The pollution is trapped near the ground.
As a country's incomes rise, urban transport pollution often first increases because
- more people can afford motorbikes and cars
- public transport becomes free
- factories close
- roads become wider than needed
Show answer
more people can afford motorbikes and cars. Rising affluence increases vehicle ownership.
Explain why a city in a mountain basin may suffer worse air pollution than a coastal city.
Show answer
Surrounding mountains shelter the basin, so winds are light and cold air and pollutants become trapped, often under a temperature inversion, whereas sea breezes at the coast help disperse pollution.. Relief, trapping, compare with the coast.

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Sources

Last updated 8 November 2026. Spotted a mistake? Tell us.