The air pollution that's choking Asia is showcasing the work of Mosaic, a digital publication that explores the science of life. It's produced by the Wellcome Trust, a global charitable foundation that supports research in biology, medicine and the medical humanities, with the goal of improving human and animal health. The content is produced solely by Mosaic, and we will be posting some of its most thought-provoking work. The story was published by Mosaic on January 20 2015.

(CNN)At the age of 13, Tan Yi Han could not see the edge of his schoolyard. It was 1998 in Singapore, the wealthy city-state known for its tidy streets and clean, green image. But for much of that particular school year, clouds of smoke shrouded the skyline. The record-setting air pollution, which had begun in 1997 and lasted for months, caused a 30% spike in hospital visits. It would later be remembered as one of southeast Asia's worst-ever "haze episodes."

Haze episodes have occurred in southeast Asia nearly every year since. Back in 1998, and for years afterwards, Tan didn't think too deeply about them. Yet at some point in his late 20s, he began to wonder: where did the haze come from? And why did it keep coming back?

Dirty air

    Air pollution kills around 7 million people every year, according to the World Health Organization (WHO), accounting for one in eight deaths worldwide in 2012. The main causes of death were stroke and heart disease, followed by chronic obstructive pulmonary disease (COPD), lung cancer, and respiratory infections among children.
      It is especially bad in the Asia-Pacific region, which has a population of over 4.2 billion and high population density. China and India alone, with a combined population of around 2.7 billion, are both enormous sources and victims of air pollution.
      In 2010, 40% of the world's premature deaths caused by air pollution were in China, the world's largest emitter of carbon dioxide, according to a survey published in the Lancet. The University of Hong Kong's School of Public Health reported more than 3,000 premature deaths in the city in 2013, and the situation in many mainland Chinese cities is reckoned to be far worse. A poll by the U.S. Pew Research Center found that 47% of Chinese citizens thought air pollution to be a "very big" problem in 2013 (up from 31% in 2008) . It is now a central focus for many Chinese environmental groups and a growing source of anxiety for the country's leadership.
      Similar health concerns are building in India, where air pollution is now the fifth-leading cause of death. Between 2000 and 2010, the annual number of premature deaths linked to air pollution across India rose six-fold to 620,000, according to the Center for Science and Environment, a public-interest research and advocacy group in New Delhi. In May 2014, the WHO