Smoke from forest fires in Sumatra, Indonesia, caused the 24-hour average levels of PM2.5 – airborne particulates 2.5 microns or less in diameter – in Narathiwat and Yala to hit nearly 90 micrograms per cubic metre of air on Tuesday. The levels were almost double the Thai safe level of 50mcg and quadruple the World Health Organisation’s safety level of 25mcg.