Megacities: growth, air pollution and services

Megacity growth

A megacity has more than 10 million inhabitants. There were 33 in 2018, projected to reach 43 by 2030 (UN World Urbanization Prospects 2018). The largest in 2018 were Tokyo (37 million), Delhi (29 million) and Shanghai (26 million).

The distribution has shifted from developed countries (New York and Tokyo were early megacities) to Asia, Latin America and Africa. Causes: rural-urban migration, natural increase among young populations, and economic growth that concentrates jobs, investment and TNC activity in a few large cities. Some megacities in developed countries are growing slowly or not at all.

Air pollution and services

• Air pollution: fine particles (PM2.5) and nitrogen dioxide from vehicles, coal burning, industry, construction dust and waste burning; worsened by temperature inversions and still weather. Health effects: respiratory and heart disease, lung cancer, especially for children and older people.
• Beijing: after an air pollution control programme from 1998, intensified in 2013, PM2.5 fell 35% in Beijing and 25% in surrounding regions between 2013 and 2017, through energy restructuring, coal-fired pollution control and vehicle emission controls (UNEP).
• Services: water supply and sanitation, waste collection, transport and electricity often lag behind growth, causing water-borne disease, flooding and congestion.

Negative impacts are not only found in developing countries: developed megacities also face congestion, air pollution and housing costs.

Skill (12): mean, mode, median and range

Practice data (invented) for daily PM2.5 in micrograms per m3 over one week: 48, 62, 55, 91, 55, 120, 73.

• Mean = sum / number of values.
• Median = middle value when ranked.
• Mode = most frequent value.
• Range = highest - lowest.

The median is less affected than the mean by a single extreme day, such as a smog episode.

Worked example

Find the mean, median, mode and range of the practice PM2.5 data 48, 62, 55, 91, 55, 120, 73.

1. Sum = 504; mean = 504 / 7 = 72.0
2. Ranked: 48, 55, 55, 62, 73, 91, 120; median = 62
3. Mode = 55
4. Range = 120 - 48 = 72

Answer: Mean 72.0, median 62, mode 55, range 72.

Check yourself

1. Practice data (invented): daily NO2 readings of 40, 52, 47, 61 and 50. Calculate the mean.
   Show answer

   50. 250 / 5 = 50.

2. Practice data (invented): PM2.5 readings of 35, 80, 42, 150, 61, 58. Find the median.
   Show answer

   59.5. Ranked: 35, 42, 58, 61, 80, 150; median = (58 + 61) / 2 = 59.5.

3. Using the practice data 35, 80, 42, 150, 61, 58, find the range.
   Show answer

   115. 150 - 35 = 115.

4. Megacities are projected to increase from 33 (2018) to 43 (2030). Calculate the percentage increase to 1 decimal place.
   Show answer

   30.3 %. 10 / 33 x 100 = 30.3%.

5. A megacity is a city with
   • more than 1 million inhabitants
   • more than 10 million inhabitants
   • the highest GDP in its country
   • a population growth rate of over 5%
   Show answer

   more than 10 million inhabitants. The UN definition uses 10 million.

6. Which is a major source of PM2.5 in megacities?
   • Wind turbines
   • Parks and gardens
   • Rainfall
   • Vehicle exhaust and coal burning
   Show answer

   Vehicle exhaust and coal burning. Combustion produces fine particles.

7. Explain how air pollution in megacities affects human health.
   Show answer

   Fine particles such as PM2.5 are breathed deep into the lungs, causing respiratory and heart disease, asthma and lung cancer, especially in children and older people.. Pollutants enter the lungs and cause respiratory and heart disease.

Practise with instant feedback Print this lesson

Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Geography specification (Issue 3, September 2025)
• UN DESA: World Urbanization Prospects 2018 press release (16 May 2018)
• UNEP: A review of 20 years' air pollution control in Beijing
• Pearson principal examiner report, WGE01 Global Challenges, June 2025

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