Worst air pollution in the world: Beijing, Delhi, Ahwaz, and Ulaanbaatar.

Which City Has the Worst Air Pollution in the World?

Which City Has the Worst Air Pollution in the World?

Health and medicine explained.
March 5 2013 11:40 AM

Where Is the Worst Air in the World?

Beijing gets a lot of attention for its pollution, but it’s nowhere near the top of the list.

Vendors selling drinks stand beside vehicles near the India Gate war memorial on a smoggy day in New Delhi February 1, 2013.
A smoggy day in New Delhi this winter near the India Gate war memorial

Photo by Adnan Abidi/Reuters

I wake up and suck a bowl of charred asbestos through a dirty bong.

Well, that’s what it feels like most winter mornings when I open the door of the fourth-floor New Delhi apartment that I currently call home. Fog-drenched clumps of soot, ozone molecules, and microscopic bundles of nitrogen oxides flow down my trachea and into my chest, where some become lodged. Some of these particles might give me lung cancer. Others will enter my bloodstream, further inflaming old ankle and finger injuries. The airborne detritus puts me in danger of contracting bronchitis, asthma, a lung infection, even hypertension and dementia.

China’s appalling air quality made headlines around the world this winter. But people living in New Delhi and in dozens of other cities throughout the developing world consistently endure air with heavier loads of soot than do the residents of Beijing. While most Americans and Europeans now enjoy cleaner air than they did for much of the last century, air pollution is worsening in Asia, claiming millions of lives every year.


After weeks without a trip outside of Delhi, I gradually stop noticing the filth in the air. There are exceptions, of course, such as that hostile blast of moist air on a foggy winter morning. Or when I’m sitting at a stoplight in an open-air auto rickshaw, feeling fumes wash over me from a honking swarm of vehicles. Or when a layer of darkness veils my drying clothes, coats the inside of my nose, or hangs heavy along a horizon.

With every breath, regardless of how mindful or oblivious I am of the poison that’s filling my lungs, my risk of suffering a stroke or a heart attack increases.

An estimated 3.2 million people died prematurely in 2010 because of the poisonous effects of outdoor air pollution, according to the findings of an exhaustive study of global causes of death published in December in the Lancet. Two-thirds of those killed by air pollution lived in Asia, where air quality continues to worsen.

Outdoor air pollution has become India’s fifth highest killer. Only tobacco, high blood pressure, indoor air pollution (typically caused by poorly ventilated stoves), and diets that are poor in fruit and vegetables kill more people here.

The most vulnerable to air pollution are children, the elderly, and people already suffering from respiratory or cardiac illness, says Anumita Roychowdhury, an air pollution expert at the Delhi-based nonprofit Center for Science and Environment. Even fit adults in the prime of their lives are at risk. The dangers range from cancer to hypertension, diabetes, and birth defects. “We need to be extremely careful,” says Roychowdhury.

Air pollution levels in China recently reached dizzying new heights. An air quality monitor operated by the U.S. Embassy detected a spectacular spike in pollution levels in Beijing in January and broadcast them over Twitter. The media frenzy helped force the country’s rulers to pledge to take steps to clean the city’s air, such as removing polluting vehicles from the streets.

“Beijing was filthy,” says Mark Bagley, a San Francisco resident who visited Asia recently. “The rain and snow were gray to dark gray with minimal visibility—maybe two blocks at most. Rain that pooled in the gutters looked black.”

But according to World Health Organization data covering more than 1,000 cities in 91 countries, China’s capital is not the city that consistently endures the world’s worst air pollution. It doesn’t even come close.

One of the crucial measures of dangerous air pollution is the number of parts per million of particles smaller than 10 micrometers (PM10) wafting through the air. Beijing’s residents breathe in air with an average PM10 of 121, but millions of people have it worse.

The rankings, cobbled together using air monitoring data from a variety of sources between 2003 and 2010, suggest that the world’s worst air pollution floats over Ahwaz, a city in southwestern Iran where the average PM10 level hovers around 372. Mongolia’s capital, Ulaanbaatar, ranks second, enduring a 279 PM10, far higher than the global average of 71.