A Beijing cyclist wearing a face mask for prevention from pollution. Credit:AFP 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 non-profit Centre 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.

Congestion on Beijing's third ring road on a smoggy day in January, 2013. Credit:Reuters Air pollution levels in China recently reached dizzying new heights. An air quality monitor operated by the US 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. But according to World Health Organisation data covering more than 1000 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. An elderly couple wears masks as protection against air pollution in Beijing. Credit:AFP One of the crucial measures of dangerous air pollution is the number of parts per million of particles smaller than 10 micrometres (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 south-western 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. The view from the Fairfax Media Beijing office at lunchtime on January 29, 2013. Credit:Sanghee Liu Farther down the list are more cities in Iran, along with some in India, Pakistan, and Botswana, before Delhi appears in the 12th spot, with average particulate levels of 198 parts per million. To Americans, Asia's air pollution woes may seem a world away. But it is a small world. Pollution travels east along jet streams from Asia to the North American west coast. Research indicates that nearly one-third of the soot in the San Francisco Bay Area blew over from Asia. The most polluted region in the United States, according to the WHO's air quality data, is in California's Central Valley, where industrial and exhaust pollution gets trapped inside an expansive bowl of rock that's home to farms, heavy industry, and millions of people. But the valley city of Bakersfield, America's No. 1 air pollution hotspot, ranked just 276th in the WHO's list, with an average PM10 count of 38 parts per million.

I lived for a year in the Central Valley and the ambient pollution can be sickening. But it doesn't compare to that in Delhi. Here, it feels like I'm drawing tiny fibers deep into my respiratory system. They seem tangibly solid against my spongy insides. Clean air regulations and technological advances have helped scrub the West's air. That is not the case in many developing countries. "We could easily have taken a cleaner pathway of development," says India's Rajendra Pachauri, who chairs the Intergovernmental Panel on Climate Change. He pointed out that cities such as Pittsburgh and London have recovered from terrible air pollution from when the United States and the United Kingdom were at earlier stages of development. "Unfortunately, we have not learned from those examples." The New York Times' India Ink blog reported that air pollution was more than twice as bad in Delhi on January 31 as it was in Beijing. There are 46 cities, in such countries as the United Arab Emirates, Saudi Arabia, Egypt, India, Mexico, and Nigeria, where average pollution levels exceed those of Beijing. Overall, India recently ranked last in a list of 132 countries surveyed for their air quality.

Most of the pollution that I inhale in Delhi comes from diesel-burning trucks and buses. Other aerial filth that enters my lungs broke away from petrol as it combusted incompletely in cars and from natural gas burned by auto rickshaws. Coal-fired power plants and agricultural burning take a toll, as do makeshift campfires that line the streets at night during the winter, where everything from leaf litter and cow dung to rubber motorcycle saddles are burned for warmth. It's not that officials here don't care. Efforts to cut pollution from vehicles in Delhi in the late 1990s and early 2000s, by taking such steps as switching auto rickshaws over to natural gas and requiring annual vehicle inspections, helped clear the air. But as the city's wealth grows, it is experiencing an explosion in the number of cars and other vehicles on its roads, pushing air pollution levels back up again. The Indian Express newspaper recently reported that Delhi's environment department is mulling a suite of efforts to tackle the problem anew, such as promoting public transit, jacking up parking fees, shuttering coal-fired power plants, and more harshly penalising those who break pollution rules. But as is the case in so many other cities in developing countries throughout Asia, economic progress and the clamour for trade, travel, and newfound luxuries are proving no match for incipient government programs that aim to protect people from bad air. After just six months in India, I'm growing accustomed to occasional fits of coughing and hacking. I hold American and Australian passports, and even as a freelance journalist I'm wealthy by local standards, making it easy to leave Delhi whenever I am ready.

But for a substantial portion of the planet's population, some of them Chinese but many of them living in countries where pollution woes go little noticed by Western journalists, there would seem to be little hope of gulping at the fresh air that so many people in other parts of the world take for granted. Slate.com