SINGAPORE, Sept 4 — Singapore’s air quality slipped into the unhealthy range today for the first time because of haze since October 2023, as smoke from forest and land fires across the region continued to worsen.

The 24-hour Pollutant Standards Index (PSI) in central Singapore reached 101 at 7am today, The Straits Times reported, citing data from the National Environment Agency (NEA).

A PSI reading of between 101 and 200 is classified as unhealthy, with the public advised to reduce prolonged or strenuous outdoor activity.

Readings had begun edging towards the unhealthy threshold in the early hours of today. At 1am, PSI levels across Singapore were between 70 and 90, still within the moderate range, before the central region rose to 99 by 6am.

The deterioration follows weeks of forest and land fires in Sumatra and Kalimantan in Indonesia, where dry conditions have fuelled an increase in hot spots and smoke haze.

Singapore’s Meteorological Service warned on September 1 that the Republic could experience hazy conditions over the following two weeks as dry weather persisted across the surrounding region.

It said dense smoke haze had been observed over southern and central Sumatra and parts of Kalimantan on most days since around August 21.

How severely Singapore is affected will depend largely on prevailing winds.

Malaysia has already been hit hard by the haze, with unhealthy air recorded across several states.

In Sarawak, among the worst-affected areas, Serian recorded an Air Pollutant Index reading of 408 at 8pm yesterday, placing it in the very hazardous category. Four other areas in the state recorded very unhealthy readings.

Singapore authorities have also stepped up public health preparations.

The country’s Haze Task Force told The Straits Times on August 24 that efforts had been intensified to raise awareness of the increased haze risk and advise the public on how to protect their health.

Doctors have been reminded to advise vulnerable groups, including elderly people, pregnant women, children and those with heart or lung conditions, to take precautions.

Schools have also been told to conduct visual checks on students’ well-being, while haze advisories have been issued to workplaces.

The NEA uses both the 24-hour PSI and one-hour PM2.5 readings to assess air quality during haze episodes.

The 24-hour PSI is intended to guide plans for outdoor activity over the following day, while the one-hour PM2.5 reading is more useful for immediate decisions, such as whether to go for a run.

PM2.5 refers to fine particles commonly found in smoke haze from forest fires that can penetrate deep into the lungs and enter the bloodstream.

Air quality is classified as good when the PSI is between zero and 50, moderate between 51 and 100, and unhealthy from 101 to 200.