Visualized: Air Quality and Pollution in 50 Capital Cities

We know bad air quality when we breathe it in—but how does it measure and compare across different cities?

To assess air quality, agencies measure the amount of particulate matter in an area to arrive at a number the resident population is breathing in over a period of time.

In this case, Planet Anomaly visualized the concentration of PM2.5 (fine particulate matter) in 50 select capital cities across the globe, using data from IQAir’s 2022 World Air Quality Report.

The report applied population-based adjustments to standardize its results and calculated an annual average of the data. If a city exceeded the WHO safety guideline of 5 micrograms per cubic meter (μg/m³) for annual average PM2.5 levels, it implied potential health risks for its residents.

At the top of the list with the best air quality, Canberra, the capital of Australia, had an average PM2.5 level of 2.8 μg/m³ in 2022. Vehicle emissions and dust storms are the few sources of air pollutants in the city.

However, while Canberra did well in 2022, it had some of the worst air quality in 2020 when bushfire smoke blackened the skies.

Here’s the full list of all 116 capital cities measured by IQAir’s report, ranked by air quality from best to worst.

Hamilton, Bermuda (3.8 μg/m³) and Reykjavik, Iceland (3.3 μg/m³) rank second and third respectively, followed by three more capitals on island nations. In fact, nine of the top 10 capitals are situated directly on a coastline and take advantage of ocean breezes that can act as air filters.

Ranked 8th, the Port of Spain (capital of Trinidad & Tobago) is the last city whose air quality is considered safe (5.0 μg/m³) by the WHO.

From a broader perspective, fewer than 10% of all countries have air quality that meets safety guidelines.

Meanwhile, at the bottom of the list with the worst air quality, Chad’s capital city N’Djamena, recorded a PM2.5 concentration of nearly 90 μg/m³ per day in 2022—almost 18x the recommended WHO safety guideline.

Perhaps the most striking feature of the rankings is how air quality worsens with countries that are in the low and middle-income categories and improves in high income countries.

As an example, compare the distribution of the ranks of capital cities in Asia (generally lower and middle income countries) versus capitals in Europe (general high income countries).

The majority of European capital cities are ranked 20–60 versus Asian capitals which are mostly ranked 60–100.

Lower and middle income countries have larger structural economic concerns and many of them are still in the process of transitioning away from polluting materials that affect air quality.

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