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 per cent spike in hospital visits. It would later be remembered as one of Southeast Asia's worst-ever "haze episodes".
Haze episodes have occurred in South-east 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?
Air pollution kills around 7 million people every year, according to the World Health Organisation (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 per cent 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 US Pew Research Center found that 47 per cent of Chinese citizens thought air pollution to be a "very big" problem in 2013 (up from 31 per cent 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 Centre for Science and Environment, a public-interest research and advocacy group in New Delhi. In May 2014, the WHO said that New Delhi had the worst air of 1,600 cities surveyed worldwide and that rising air pollution had increased the risk of strokes, cancers and heart disease.
Another 2014 study has linked a significant drop in India's wheat and rice crop yields to rising levels of two air pollutants - black carbon from rural cooking stoves and ground-level ozone formed from motor vehicle exhausts, industrial emissions, and chemical solvents - between 1980 and 2010.
In both China and India, air pollution is one consequence of a massive exodus from farm to city that has occurred in recent decades. The change has contributed to rising emissions from both vehicles and factories, especially coal-fired power plants, and an emerging middle class that increasingly desires a range of consumer goods that are common in Europe and the United States.
South-east Asia has encountered similar problems in recent decades as its economies and populations have boomed. In fact, according to the WHO, nearly one million of the 3.7 million people who died from ambient air pollution in 2012 lived in South-east Asia.
But on top of smokestacks and tailpipes, the region faces an added burden: smoke haze produced in Indonesia that is a by-product of the world's US$50 billion palm-oil industry.
In the summer of 2013, a plane carried Tan Yi Han over the Straits of Malacca to Pekanbaru, the capital of Riau province, the largest palm-oil production region in Indonesia. Tan, then a 28-year-old financial consultant, was volunteering with the Global Environment Centre, a Malaysian group that has worked for years to prevent and mitigate haze. He travelled to the heart of neighbouring Indonesia, just after a record-breaking haze episode hit peninsular Malaysia.
On a driving tour in Riau, he saw endless acres of burned-out landscapes. Fires had turned swampy peat bogs, the area's natural vegetation, into land whose parched surface resembled charcoal. These fires are to dry out the peatlands for agricultural uses, mainly the cultivation of oil palms. But in some villages, fires had even destroyed existing oil palm trees that belonged to multinational companies or local farmers.
Tan had a memorable encounter in the village of Rantau Bais. A couple there plied him with tea and snacks, then quietly asked if he could spare any of his own food for them. Their daughter had developed a respiratory problem because of the haze. The surprise medical bill, coupled with the fire destroying their oil palm crops, had left the family penniless and hungry.
Until that moment, he had mostly thought of peat blazes as "forest fires," as they are often called in media reports. But here was a visceral reminder that the fires affect working land and real people. "It really touched me," said Tan. "I made a promise to myself that I'd do my best to prevent them from suffering from fires again."
It was an issue, he felt, that required far more public discussion - and when the time was right, action. "I must get more people involved," he had thought, "and turn this into a movement."