Poor visibility & burning smell are not necessarily good indicators of PSI levels

Now you know.

Fasiha Nazren | September 22, 2019, 03:49 PM

The 24-hour PSI as of 2pm on Sep. 22 was in the Unhealthy range while the 1-hour PM2.5 reading was one the Elevated range.

24-hour PSI. Via NEA.

1-hour PM2.5 via NEA.

And it doesn't seem to let up thanks to several hotspots in Indonesia. A total of 755 hotspots were detected just yesterday (Sep. 21).

More smoke sighted = higher PSI?

To some, the haze may appear worse than the PSI indicates.

One question many would probably pose: How can such a smog be just "borderline unhealthy" in the PSI range?

Photo by Julia Yeo

Water-bound particles can cause low visibility

According to the National Environment Agency (NEA), poor visibility doesn't mean the air is more polluted.

The amount of water vapour in the air is a significant factor in visibility.

Water droplets scatter light, thus, resulting in lower visibility.

In addition to that, some air pollutant particles also attract water molecules, resulting in larger particles that scatter more light.

These particles, in turn, cause poor visibility to go on for a longer period.

What this means is that high humidity and rain, on top of the smoke from the haze, can cause the visibility to be much lower.

Burning smell =/= higher PSI

Another factor that people associate with haze is a strong, burning smell.

However, this again isn't necessarily an indicator of an increase in the PSI reading.

According to NEA, transboundary haze affecting Singapore mainly arises from forest and peat fires in the region.

Apart from generating smoke particles, the vegetation and peatland fires also generate a complex mixture of gases which can cause the burning smell.

You can read more here.

A haze expert explains what causes the haze and how you can do your part to fight it:

Top image by Julia Yeo.