SMOGGY skies on Tuesday and Wednesday are due to hotspots in Myanmar, Thailand and Laos, which are going through their dry season, said the National Environment Agency, which monitors air quality.
Its regional haze map showed clusters of hotspots in the northern Asean region, along with localised smoke plumes in Laos.
"With the weakening of winds over Singapore in recent days, the accumulation of increased particulate matter in the air could have led to the current hazy condition," an NEA spokesman said.
Winds are light and variable during the current inter-monsoon period between the North-East and South-West monsoons, which typically lasts from late March to May.
At 4pm on Wednesday, the PSI, a measure of air pollution, was between 39 and 53, in the good to moderate range. The level of PM2.5, or very fine particulate matter, was between 25 and 39 micrograms per cubic metre.
While those levels did not trigger any health advisories for the general population, unusually sensitive people should consider reducing prolonged or heavy exertion, the NEA said.
The hazy condition is expected to persist over the next few days and NEA will continue to monitor the situation, said a spokesman.
Air quality readings and health advisories are available at http://www.nea.gov.sg/psi, or at the Weather@SG website http://weather.nea.gov.sg, on Twitter @NEAsg, by calling 1800 CALL NEA (1800 2255 632), or via the myENV iPhone or Android app.