CNN.com 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."