All but one of the 100 cities with the world's worst air pollution last year were in Asia, according to the sixth Annual World Air Quality Report by IQAir, which tracks air quality worldwide.

Most of these cities were in India - 83 - and they exceeded the World Health Organization's air quality guidelines by more than 10 times, said the report.

The study looked at fine particulate matter, or PM2.5, the WHO-specified annual guideline.

The region of Central and South Asia was home to the top ten most polluted cities in the world.

The most polluted country in 2023 was Bangladesh. Measured at 79.9 µg/m3, its air pollution level is more than 15 times higher than the WHO annual PM2.5 guideline.

Begusarai, a city of half a million people in northern India’s Bihar state, was the world’s most polluted city last year with an average annual PM2.5 concentration of 118.9 — 23 times the WHO guidelines. It was followed in the IQAir rankings by the Indian cities of Guwahati, Assam; Delhi; and Mullanpur, Punjab.

Commenting on the IQAir recent report, Avinash Chanchal, Campaign Manager, Greenpeace India said, “The data indicates pressing environmental challenges that India faces, posing significant health risks to its vast population. Vehicle emissions continue to play a significant role in exacerbating air pollution, accounting for 40% of PM2.5 emissions in the nation’s capital.”

Across India, 1.3 billion people, or 96% of the population, live with air quality seven times higher than WHO guidelines, according to the report.

Central and South Asia were the worst-performing regions globally, home to all four of the most polluted countries last year: Bangladesh, Pakistan, India and Tajikistan.

South Asia is of particular concern, with 29 of the 30 most polluted cities in India, Pakistan or Bangladesh. The report ranked the major population centers of Lahore in 5th, New Delhi in 6th and Dhaka in 24th place.

In Asia, however, pollution levels rebounded across much of the region, said CNN.

China reversed a five-year trend of declining levels of pollution, the report found. Chinese cities used to dominate global rankings of the world’s worst air quality but a raft of clean air policies over the past decade has transformed things for the better.

A study last year found the campaign meant the average Chinese citizen’s lifespan is now 2.2 years longer. But thick smog returned to Beijing last year, where citizens experienced a 14% increase in the annual average PM2.5 concentration, according to the IQAir report. China’s most polluted city, Hotan, was listed at 14 in the IQAir ranking.

In Southeast Asia, only the Philippines saw a drop in annual pollution levels compared to the previous year, the report found.

Indonesia was the most polluted country in the region, with a 20% increase compared to 2022. Indonesia, Vietnam and Thailand all had cities that exceeded WHO PM2.5 guidelines by more than 10 times, according to the report.

Last month, Thai authorities ordered government employees to work from home due to unhealthy levels of pollution in the capital Bangkok and surrounding areas, according to Reuters. Last week, tourism hot spot Chiang Mai was the world’s most polluted city as toxic smog brought by seasonal agricultural burning blanketed the northern city.

While the number of countries and regions with air quality monitoring has steadily increased over the past six years, there remain significant gaps in government-operated regulatory instrumentation in many parts of the world. Low-cost air quality monitors, sponsored and hosted by citizen scientists, researchers, community advocates, and local organizations, have proven to be valuable tools for reducing gaps in air monitoring networks across the world.

“A clean, healthy, and sustainable environment is a universal human right. In many parts of the world the lack of air quality data delays decisive action and perpetuates unnecessary human suffering. Air quality data saves lives. Where air quality is reported, action is taken, and air quality improves,” states Frank Hammes, Global CEO, IQAir.

These independent air quality monitoring stations reveal disproportional exposure to harmful air pollution among vulnerable and underrepresented groups. Glaring gaps in air quality monitoring data, where pollution is likely poor, further underline the need to expand air quality monitoring coverage worldwide.

For this year’s report, data from more than 30,000 air quality monitoring stations across 7,812 locations in 134 countries, territories, and regions were analyzed by IQAir’s air quality scientists.

Key findings from the 2023 World Air Quality Report:

•  Seven countries met the WHO annual PM2.5 guideline (annual average of 5 µg/m3 or less): Australia, Estonia, Finland, Grenada, Iceland, Mauritius, and New Zealand.
•  The top five most polluted countries in 2023 were:
•  Bangladesh (79.9 µg/m3) more than 15 times higher than the WHO PM2.5 annual guideline
•  Pakistan (73.7 µg/m3) more than 14 times higher than the WHO PM2.5 annual guideline
•  India (54.4 µg/m3) more than 10 times higher than the WHO PM2.5 annual guideline
•  Tajikistan (49.0 µg/m3) more than 9 times higher than the WHO PM2.5 annual guideline
•  Burkina Faso (46.6 µg/m3) more than 9 times higher than the WHO PM2.5 annual guideline
•  A total of 124 (92.5%) out of 134 countries and regions exceeded the WHO annual PM2.5 guideline value of 5 µg/m3.
•  Africa remains the most underrepresented continent, with a third of the population still lacking access to air quality data.
•  Climate conditions and transboundary haze were major factors in Southeast Asia, where PM2.5 concentrations rose in nearly every country.
•  The region of Central & South Asia was home to the top ten most polluted cities in the world.
•  Begusarai, India was the most polluted metropolitan area in 2023. India was home to the four most polluted cities in the world.
•  The most polluted major U.S. city was Columbus, Ohio. Beloit, Wisconsin was the most polluted city in the U.S.
•  Las Vegas, Nevada was the cleanest major city in the U.S.
•  For the first time in the history of this report, Canada was the most polluted country in Northern America, with the region's 13 most polluted cities located within its borders.
  • Agencies