SINGAPORE - The air quality entered the moderate range in the early hours of Sunday and remained so up to the early afternoon.
The three-hour Pollutant Standards Index (PSI) hit 67 at 1am and climbed slowly but steadily up to 79 at 2pm.
The PSI readings also hit around 70 last Thursday and the Meteorological Services said it was due to the weakening of winds that led to an accumulation of particulate matter in the atmosphere.
It added that the low level winds were expected to continue to blow from the northeast for the next two months.
The National Environment Agency said on Jan 22 that there has been an early onset of dry weather, with the rainfall for January expected to be "significantly below average".
February is also forecast to experience less rainfall than usual.
NEA recommends that normal activities be carried out when the 24-hour PSI is in the moderate range of 50-100.
If the 24-hour index hits the unhealthy band (101-200), healthy people should reduce prolonged or strenuous outdoor physical exertion, while the elderly, pregnant women and children should minimise such exertion.
The current index includes PM2.5, which are small, toxic particles, in its assessment of air quality.