Singapore experienced slight haze on Tuesday morning, as the Pollutant Standards Index's (PSI) three-hour reading crept into the moderate range. It stood at 51 as of 11am.
Air quality had gradually worsened overnight from a reading of 33 at midnight on Tuesday morning.
The National Environment Agency (NEA) had said in an advisory on Sunday that although prevailing north-easterly winds would keep haze from Sumatra, Indonesia, away from Singapore for several days, "occasional slight haze" could occur. This was particularly so in the mornings, as a result of the accumulation of particulate matter under stable atmospheric conditions.
The Riau province of Sumatra has been shrouded in dense haze over recent days as farmers set fires to clear land during the dry spell. The NEA detected 70 hotspots in Sumatra on Sunday, and noted that smoke plumes were visible in Riau.
Singapore is in the midst of one of its longest spells of dry weather in years, with barely any rain over the past month and a half. Minister for the Environment and Water Resources Vivian Balakrishnan had warned last Friday that the combination of prolonged dry weather and fires would lead "inevitably to an increase in haze".
The same day, the head of the Meteorology, Climatology and Geophysics Agency (BMKG) station in Pekanbaru, Indonesia, Mr Sugarin, predicted that north-easterly winds had begun to reverse, increasing the chances of haze affecting Singapore.
Tracking the haze in Singapore and Malaysia
Map by Google