On Oct. 7, 2023 morning, the air quality in some parts of Singapore entered the "unhealthy" range. This is the first time since 2019.

The National Environment Agency's (NEA) said that hazy conditions are likely to persist through the weekend.

Air quality in Singapore

According to NEA's haze.gov.sg website, which monitors one-hour PM2.5 levels and 24-hour Pollutant Standards Index (PSI) levels, the air quality in the central and eastern part of Singapore is within the "unhealthy" range.

What is PSI and PM2.5?

PM2.5 measures the amount of airborne fine particles that are 2.5 microns or smaller.

Unhealthy levels of PM2.5 can increase the risk of health problems like heart disease, asthma, and low birth weight, reduce visibility, and cause the air to appear hazy.

The PSI is computed based on a 24-hour average of concentration levels of PM2.5, among other pollutants.

Central and eastern part of Singapore in "unhealthy" range

At the time of writing, the air quality in the central and eastern parts of Singapore has declined.

The 24-hour PSI in the central and eastern parts of Singapore are at 102 and 111 respectively.

These fall within the 101 to 200 PSI range where air quality is considered to be "unhealthy".

On the other hand, the air quality in the southern, northern, and western regions of Singapore remains within the "moderate" range, where the 24-hour PSI are 87, 68, and 62 respectively.

The air quality is moderate if the 24-hour PSI is between 51 and 100.

The air quality is considered very unhealthy and hazardous when the 24-hour PSI breach the 201-300 and above 301 ranges respectively.

The last time the 24-hour PSI was higher than 80 was in 2019.

Here are the one-hour PM2.5 levels at the time of writing.

Haze likely to affect Singapore over Oct. 7-8 weekend

NEA said on Oct. 6, 2023 that there is a likelihood of haze affecting Singapore over the weekend if the fires in Sumatra, Indonesia persist, and if the wind direction is unfavourable.

There has been a significant increase in the number of hotspots in Sumatra, with 212 detected on Oct. 6.

This is a sharp increase from the 65 and 15 hotspots recorded on Oct. 5 and Oct. 4 respectively.

Smoke plumes and haze were observed from satellite imagery over southern and central Sumatra.

A brief shift in the wind direction, from southeasterly to southerly, on Oct. 6, 2023 afternoon blew some of the lighter haze toward Singapore and caused a deterioration in air quality.

The agency added that it will begin providing daily haze advisories from the evening of Oct. 7, 2023 .

Top image from haze.gov.sg website and by Mothership