The air pollution that's choking Asia

By Mike Ives, MOSAIC

Updated 1532 GMT (2332 HKT) January 30, 2015

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A haze has periodically wafted over Southeast Asia for 20 years. It is especially bad in the Asia-Pacific region, which has a population of over 4.2 billion and high population density. Pictured, smog hovers above the Kuala Lumpur skyline in June 2013.

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Smoke billowing from fires in areas surrounded by plantations in Riau province, on Indonesia's Sumatra island, about 173 miles west of Singapore on June 17 2013. On June 20, Singapore demanded "definitive" action by Indonesia on forest fires raging in Sumatra as the nations prepared for emergency talks to ease the severe smog enveloping Singapore.

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A woman walks through haze as a forest fire burns bushes and fields, June 27, 2013 in Riau province, Indonesia. The fires on Sumatra caused record smog levels in Malaysia and Singapore. Sumatra was forced to step up efforts to fight the fires to relieve conditions, with eight farmers arrested for starting the fires.

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Burned trees and clearing in protected peatland in Riau province, June 29 2013. Environmentalists say that illegal slash and burn method is a widespread method of clearing land.

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Indonesian motorists travel under a blanket of haze in Dumai town, Riau province, March 3, 2014.

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March 1 2014, In Medan, Indonesia, construction workers toil in the setting sun as smoke from fires in Riau province covers the region. The province was at the heart of a Southeast Asian smog crisis in 2013 and declared a state of emergency in February 2014 after being blanketed in a thick haze from forest fires.

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Singapore's skyscrapers enveloped in smog, 16 October 2006, from forests fire in Indonesia. The annual recurrence of carbon-rich haze caused by fires in Indonesia's vast tropical peatlands may help fuel global warming if left unchecked, experts have warned.

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A man practices Tai Chi in Shanghai as heavy smog engulfs the city on November 7, 2013. In 2010, 40% of the world's premature deaths caused by air pollution were in China, according to a survey published in the Lancet.

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(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.