SINGAPORE - Air quality that took a hit on Monday (Oct 12) is not set to improve on Tuesday (Oct 13), the National Environment Agency (NEA) said.

In its Monday evening update on the haze situation, the agency said that the 24-hour Pollutant Standards Index (PSI) for the next 24 hours is set to be between the high end of the moderate range and the low end of the unhealthy range.

That is where the 24-hour PSI reading has hovered throughout Monday, after the haze worsened in the morning. It crept back into the unhealthy range at 1am, after staying in the moderate band for the better part of last week.

The deterioration was due to haze in the surrounding region being blown in by weak prevailing winds, the agency said. Some 125 hotspots were detected in Sumatra on Monday.

As of 11pm, the 24-hour PSI stood at 97-116 - in the high end of the moderate range and low section of the unhealthy range.

The three-hour PSI, which is not tied to a health advisory, was 107.

A multinational effort to combat the forest fires still raging in Sumatra began in earnest on Sunday, with Singapore playing its part by sending a Chinook helicopter equipped with a 5,000-litre water bucket.

More help from countries including Australia and Russia is expected to arrive over the course of the week.

For local haze updates, visit the NEA website (www.nea.gov.sg), the haze microsite (www.haze.gov.sg), follow NEA on Facebook (www.facebook.com/NEASingapore) and NEA Twitter (@NEAsg), or download the myENV app.