Improve haze updates

I refer to the report, “PM2.5 levels hit 471 as haze situation worsens” (Oct 20). When I checked the National Environment Agency’s haze microsite on Oct 19 at 10pm, I was shocked at the one-hr PM2.5 concentration: 442 microgrammes per cubic metre.

I noted a wide variation in the various data. The 24-hour PM2.5 was 89, which translated into a Pollutant Standards Index of 138, and the three-hour PSI was 152.

The NEA does not translate the one-hour PM2.5 reading into a PSI sub-index. I looked at the real-time reporting on the AQICN website, and the PSI was 214. We can see that the NEA’s averaged data is not current.

Also, most people are unfamiliar with microgrammes per cubic metre as a measurement unit and with its associated health advisories. Officially, our health advisory is tied the 24-hour PSI, and not to the three-hour PSI or the one-hour PM2.5 reading.

That the NEA’s one-hour PM2.5 reading was 442 was alarming, given that the 24-hour PM2.5 unhealthy range is 56 to 15 microgrammes per cubic metre. Since there is no health advisory for one-hour PSI, the sensible, safe approach is to adopt the 24-hour advisory.

The United States’ Environmental Protection Agency adopts a 24-hour PM2.5 air quality standard of 35 microgrammes per cubic metre, which is more stringent than Singapore’s.

In conclusion, the NEA must improve its method of haze reporting, which is now confusing and not current. The 24-hour PSI does not tell us what our real-time exposure would be, for us to proactively take precautions.

What is the point of the three-hour average PSI when it is neither current nor linked to a health advisory? The one-hour PM2.5 reflects real-time situations better but is not linked to an advisory.

The NEA should educate the public on the PM2.5 unit of measurement, provide the microgramme per cubic metre table next to the health advisory for the PSI and convert one-hour PM2.5 concentrations to the PSI.