Friday, August 26, 2016

HAZE - NEA 1 hourly averaged data is not PSI but in ug/m3

Many are not aware that there is a difference in PSI reading and ug/m3 (microgram per meter cube). This is because the health warning levels are different.

NEA 24 hour average and 3 hour average readings are in PSI. NEA 1 hour average reading is in ug/m3 (not PSI).

S'pore official health advisory is based on 24 hours average PSI reading.  However, for our personal health concern, we should base our activities on 1 hour real time reading in PSI, a reference we are familiar with.  NEA does not provide real time 1 hour data in PSI.

*Health advisory by NEA in PSI for 24 hour averaged reading:

0 -50      Good
51-100   Moderate
101-200 Unhealthy
201-300 Very Unhealthy
more than 300 Hazardous

*Health advisory by NEA in ug/m3 for 24 hour averaged reading:

less/equal 55   Normal
56-150      Elevated 
151-250    High
more than 250  Very High

It seems that NEA has changed their reference parameter this year for haze reporting in ug/m3. It has chosen to use such neutral descriptive words, which render them useless for public health reference.

**Formal descriptive reference from NEA and MOH website last year:

Index Category           PSI            24hrPM2.5 ug/m3
Good                           0-50        0-12
Moderate                   51-100      13-55
Unhealthy                101-200    56-150  
Very Unhealthy        201-300     151-250
Hazardous             above 301     above 251

Thus, on 26/8/16 at 12 noon Spore West area hitting 216 ug/m3 (not PSI) is very alarming, as it is in the very unhealthy range !


1) US EPA adopts 35 ug/m3 as unhealthy limit for 24 hrs PM2.5 which is a more stringent standard than S'pore.

2) For real time data on PSI please refer to :  - which provides real time air pollution information for more than 60 countries in the world