On Sep. 18 at around 9am, the PSI level entered the Unhealthy range at various parts of Singapore, with the south of Singapore hitting 120.

The 1-hour PM 2.5 reading was in the Elevated range (56 - 150) at 9am as well.

This follows the "slight deterioration" in air quality in the latest update by the National Environment Agency (NEA) on Sep. 17.

109 hotspots detected in Sumatra on Sep. 17

Yesterday (Sep. 17), the NEA reported that the hazy conditions was due to the increased haziness over southern Sumatra which was carried over to Singapore by prevailing winds from the south-southeast.

109 hotspots were detected in Sumatra on Sep. 17 and moderate to dense smoke haze were spotted coming from the central and southern provinces of Riau, Jambi, South Sumatra and Lampung.

The 1-hour PM 2.5 concentration readings for the following 24 hours were expected to be between Normal and Elevated levels.

The 24-hour PSI level was also expected to range between the high end of Moderate range and low end of the Unhealthy range (101 - 200).

The agency added yesterday that, depending on wind conditions, the PSI level could enter the mid-section of the Unhealthy range at around 150.

Top photo from screenshots of NEA haze website.