Among the capital cities of 134 countries and regions analyzed in the 2023 World Air Quality Report published by air purification equipment manufacturer IQAir, New Delhi ranked first with an average annual PM2.5 concentration of 92.7 micrograms per cubic meter of air.

As Statista's Florian Zandt reports, this number exceeds the most recent World Health Organization goal 17 times, and only one other capital city comes close in IQAir's ranking.

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Dhaka, the capital of Bangladesh, exhibited an annual average PM2.5 concentration of 80.2 micrograms per cubic meter of air, followed by Ouagadougou (Burkina Faso), Dushanbe (Tajikistan) and Baghdad (Iraq) with 46.6, 46.0 and 45.8 micrograms, respectively.

The first capital city not located in Asia or Africa on the list is Sarajevo with 28.6 micrograms.

IQAir's World Air Quality Report analyzed data from 7,812 air quality monitor stations and sensors, adding seven new African and four new Latin American countries to its covered area compared to its 2022 edition.

The biggest share of PM2.5, which stands for ambient particular matter with a diameter of less than 2.5 microns, stems from human activity, according to a 2021 paper published in nature communications.

Emissions from road transport and the energy sector are the biggest contributors to a higher concentration of PM2.5, while smaller-scale sources like agricultural waste burning can also be a factor, especially in so-called developing countries.