Air pollution is the greatest environmental threat to human health, causing more than six million deaths annually and resulting in economic costs exceeding 8 trillion US dollars. This is according to the 2022 World Air Quality Report, published on 14 March by Swiss air quality technology company IQAir. The analysis found that out of 131 countries, regions and territories surveyed, only 13 met the World Health Organisation's air quality guidelines, which stipulate an annual PM2.5 concentration of 5 μg/m³ or less in 2022, with many of these located in Oceania.

The following chart shows the vast differences in air quality around the world, with cities such as Lahore in Pakistan (97.4 μg of PM2.5 particles per m³) and Delhi in India (92.6 μg) exceeding WHO guidelines by more than 10 times. At the other end of the spectrum are cities like Reykjavik in Iceland (3.3) and Tallinn in Estonia (4.8), which are among the few cities that meet the guidelines.

The report notes that air pollution hits already vulnerable communities particularly hard, as more than 90% of pollution-related deaths occur in low- and middle-income countries. Africa, as well as Central and South Asia, have the highest population-weighted annual average PM2.5 concentrations. This is even when accounting for the huge disparities in data availability between countries, as only 19 out of 54 African countries had sufficient data to be included in this document.

IQAir defines PM2.5 concentration as the amount of fine aerosol particles with a diameter of 2.5 microns or less. It is one of the six main air pollutants commonly used in air quality classification and is widely considered the most harmful, given its prevalence in the environment and impact on health. The latter includes the triggering and exacerbation of conditions such as asthma, cancer, lung disease, heart disease and premature mortality.