Singapore is experiencing some respite from the haze on Sep. 19, 2019.

With no whiff of smokiness outdoors and a clear skyline, you might be a tad confused if you check the haze readings on the National Environment Agency's site.

The 24-hour PSI is pretty high at 117 at the time of writing, and is in the unhealthy range:

So, what's with this discrepancy between PSI readings and the clear skies you're seeing outside your window?

1-hour PM2.5 readings show real time air quality

The key is to check the 1-hour PM2.5 reading.

It calculates the average of 2.5 micron particulate matter in the past hour.

PM2.5 is the most pervasive of air pollutants and most harmful to human health.

The level of PM2.5 thus better reflects current conditions, and is a more accurate real-time measurement of the current air quality outdoors.

The 24-hour PSI readings on the other hand, reflect the average of all the readings taken in the past 24 hours.

It is also calculated based on six pollutants, including fine particulate matter, or PM2.5.

It might be less relevant to check the 24-hour PSI if you're wondering whether it's safe to head out of the house in the next 30 minutes.

Check your scenery and check PM2.5

While the PSI says 117, the NEA website shows that the PM2.5 reading is in the Normal range, or Band I, at 15 µg/m³ in the north of Singapore.

The highest PM2.5 reading is 25, in the east side, which is still within the same Normal range.

Pretty accurate.

Video by Julia Wong:

So, feel free to take advantage of the clear skies and go outside to run, play or exercise, for the time being.

Before the winds change and the haze is back.

Top photo by Chong via All Singapore Stuff