On 19/9/19 in the TODAY paper, an article was published that “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 24hr average data.
NEA’s Dr Khairunnisa Yuhya even accused aqicn.org haze reading as being ‘incorrect’ compared to NEA’s 24 hr PSI reading. Aqicn.org is not incorrect but more accurate as it is instantcast reading. Besides their data is obtained from NEA’s 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 to 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.
NEA doesn’t seem 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 readings. Emergency response team will be put on protective mask based on real-time readings. This is the same for environmental pollution; the public should base their decision on real-time reading and NOT averaged 24-hr data.
Environment pollution 24-hour data is used to gauge exposure to health issues that may arise. Public decision to wear face masks or to stay indoors should be based on real-time readings (1-hr data). It is NOT safe to base decisions on 24 hour averaged readings!
Website Aqicn.org, in their FAQ explain 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 priorities right by making the haze reading/descriptive easy for public to understand.
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