Oxygen is what keeps us alive. But air pollution is a serious issue in some parts of the world. 

In observance of this year’s World Environment Day, celebrated on June 5, today’s visual presents the world’s most polluted cities, ranked by PM2.5 levels. 

PM2.5 measures tiny airborne pollutants. Higher levels mean dirtier, more hazardous air that goes deep into the lungs and the bloodstream.

Central and South Asia were hardest hit overall.

TL;DR 

• Byrnihat city in India has the worst PM2.5 pollution, at 128.2 µg/m³, mainly due to factories and terrain traps.
• Asia leads the table, with Africa catching up due to dust and urban growth, which are causing health problems.
• Global PM2.5 levels decreased slightly in 2024, but pollution persists in some areas, with countries like India working to improve air quality.

This visualization is based on data from IQAir. 

IQAir ranks polluted cities globally based on annual average PM2.5 concentrations, which are converted into the U.S. EPA-standard Air Quality Index (AQI) to rank air quality levels from good to hazardous.

World’s Most Polluted Cities 2025

India once again has the worst pollution, with 35 of the top 50 dirtiest cities in 2024, and Byrnihat reaching 128.2 µg/m³, which is the highest and 25 times above the WHO safe limits. 

The region’s pollution originates from factories, old vehicles, fires, and coal, with no significant change from last year. 

Every city on the table exceeds WHO limits by 13–25 times, causing early deaths from heart and lung problems. 

Countries like Pakistan, Bangladesh, Chad, Kazakhstan, and China demonstrate that rapid growth without strict environmental regulations can lead to toxic air pollution. 

Although clean energy plans exist, population growth and weak enforcement continue to allow pollution to persist.

Which City is Most Polluted and Why?

Byrnihat, a border town between Assam and Meghalaya, is the world’s most polluted city in 2024, with an annual PM2.5 level of 128.2 µg/m³, more than 25 times the WHO limit. 

For context, Delhi ranks second at 108.3 µg/m³, while India accounts for 11 of the top 20 hotspots. 

With over 80 factories in the region emitting pollutants from cement, chemical, and pharmaceutical industries, air quality is poor. 

Sheltering hills trap pollution, low rainfall prevents its dispersion, and traffic exacerbates the problem.

Central and South Asia are the Most Polluted Regions

Central and South Asia are the most polluted regions in the 2024 IQAir rankings, with the top seven cities all located there. 

India has 74 of the top 100 most polluted cities, with places like Byrnihat hitting PM2.5 levels of 128.2 µg/m³. 

Rapid industrialization, car emissions, and geographical factors exacerbate pollution.

Africa also ranks high on the list, with Chad the most polluted country in the region at 91.8 µg/m³. 

Five African cities are in the top 100. Dust storms from the Sahara, burning biomass, and urban growth contribute to high PM2.5 levels. 

But there’s not enough data to rank African cities, since there’s only one air-quality station for every 3.7 million people.

What Does This Mean?

High PM2.5 pollution causes about 4.7 million deaths each year and is linked to 28% of ischemic heart disease deaths. 

It increases the risk of strokes, COPD (48% of deaths), and lung cancer (19%), while also cutting down about 2.2 years from global life expectancy in polluted areas. 

Poor air quality exacerbates respiratory infections, accounts for 30% of lower respiratory deaths, and worsens asthma in approximately 147,000 children annually. 

ELI5

India tops the global pollution rankings, with Byrnihat recording the world’s highest PM2.5 level at 128.2 µg/m³, due to factory emissions and a landscape that traps dirty air. PM2.5 refers to tiny particles in the air (30 times smaller than a human hair) that can enter the lungs and bloodstream, making them one of the most dangerous forms of pollution.

Across Asia, countries like Pakistan, Bangladesh, and China also dominate the list, while parts of Africa are catching up as dust, rapid urban growth, and industry worsen air quality and cause health problems.

Sources: 

IQAir | IndianExpress | DW | State of Global Air | WHO | EPA | Greenpeace | Livemint |Anadolu Ajansi