UPDATED: 7 Sept, 9.30PM, to add Friday's PSI readings
Singapore's PSI readings for Friday reached a high of 79 -- making it the worst air quality the city-state has seen this year so far.
According to data from the National Environment Agency's (NEA) website, the PSI readings for September has been steadily rising -- from a low of 23 at the start of the month to the highest reading of 79 on Friday morning.
However, after the record-high reading at 7am on Friday, the PSI reading then dipped to a low of 52 by 7pm.
A PSI reading of 51 to 100 means that the air quality is in the moderate range.
The onset of haze is attributed to an increase in hotspot activities in Sumatra over the past one week, interspersed with the prevailing winds blowing from the southeast or southwest during the Southwest Monsoon season, said NEA.
However, it said prevailing winds are expected to turn and blow from the southeast or south, and bring a "gradual improvement" to the hazy conditions from Friday onwards.
But for the following week, Singapore could still experience "slight hazy conditions" on some days.
NEA also said in a press release, that starting from Friday, hourly updates of the three-hour PSI readings from 7am to 7pm will be provided on their website to keep the public informed of the haze situation.
"Although the current PSI readings have not reached an unhealthy level, people with heart or respiratory ailments, the elderly and children are advised to reduce physical exertion and outdoor activities," NEA said.