On 19/9/19 in Today paper "NEA addresses questions over the veracity of PSI, as alternative air quality reading emerge". Same old story over the years every time when haze descends upon Singapore - NEA desperately defending their 24hrs average data.
NEA Dr Khairunnisa Yuhya even accused aqicn.org haze reading as being 'incorrect' compare to NEA 24 hr PSI reading. Aqicn.org is not incorrect but more accurate as it is instantcast reading. Besides their data is obtained from NEA hourly reading, so how can it be incorrect ? If NEA converts its 1 hr PM2.5 reading in ug/m3 into PSI, its reading will be very close to those of aqicn.org too.
Why does NEA not convert its hourly reading into PSI ? Their 24 hr average PSI reading is actually converted from ug/m3. The only reason for not doing so for the 1 hr reading is that they don't want the public have easy comparison. Most folks only remember the number above '100' PSI means unhealthy. But they may not be aware that 56 ug/m3 in the 1 hr reading is equivalent to above 100 PSI. The descriptive 'elevated' in 1 hr reading has the same meaning as 'unhealthy' in 24 hr averaged data. (note: as safe exposure limit for PM2.5 is base on 24 hrs, for conservative safety reason, we can base 1 hr safe expose limit on the 24 hr recommendation ie 56 ug/m3 'elevated' being the start of unhealthy range)
NEA don't seems to understand that for public safety - its 24 hr average reading is not helpful at all. As an analogy, if there is a chemical gas leak in a factory - workers will be evacuated base on real time reading. Emergency response team will put on protective mask base on real time reading. This is the same for environmental pollution - public should base their decision on real time reading and NOT averaged down 24 hrs data.
Environment pollution 24 hour data is used to gauge exposure health issues that may arises. Public decision to wear face mask or to stay indoor or not - should be based on real time reading (1 hr data). It is NOT safe to base decision on 24 hour averaged down reading !
Aqicn.org under their FAQ explains in details how they derive their reading. They also explained why they think 24 hr averaging is a "very bad idea" as air pollution is dynamic and no one can wait for 24 hrs before knowing that the air quality is good.
NEA should consider using Nowcast data formula suggested in aqicn.org website which is more reflective of haze suitition.
The NowCast is computed from the most recent 12 hours of PM monitoring data, but the NowCast weights the most recent hours of data more heavily than an ordinary 12-hour average when pollutant levels are changing. The NowCast is used in lieu of a 24-hour average PM concentration in the calculation of the AQI until an entire calendar day of hourly concentrations has been monitored."
NEA should stop being so defensive and get their priority right by making the haze reading/descriptive easy for public to understand.
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