Friday, September 25, 2015

NEA psi reading is historical averaged out data

I am not sure if I heard it correctly when our minister said when interviewed by the media broadcast during the news on 24/9/15 night that if we want hourly reading we can refer to NEA website and not use other sources.

As far as I know, NEA only provide us with processed data base on AVERAGE 24 hours and AVERAGE 3 hours reading.  The heading and the data table in the NEA website could be misleading the public to think it is spot hourly reading - it is NOT.  So is our minister also confused by his own agency website ?

The NEA data table heading does not have the word 'average' in it. It only says :

PSI Readings over the last 24 hours and 3-hr PSI Reading. It then go on to list the reading at 1am, 2am, 3am....etc.  Link to -  nea data table

It is in other area on NEA site that we find information on how the their psi reading is derived and the formula use.  Quote from NEA website :

For PM2.5, the new 24-hour PSI reflects the PM2.5 concentration levels averaged across 24 hours. The new 3-hour PSI reflects the PM2.5 concentration levels averaged across 3 hours

So it means if the 24 hrs reading at 1 am states it is 200 psi, it is average reading from 1 am yesterday to 1 am today. If it is 3 hrs average at 6 pm, it means the reading is average from 3 to 6pm.

There have been public feedback for years that NEA should provide us with hourly spot reading. Real time data is more useful and safer than past historical averaged data in making decision.  For example, if the school has a basket ball game that day at 10 am, real time data can help decide if the event can continue without compromising on students health. Besides due to averaging effect, the time NEA reading says we are hit by hazardous range is normally delay by 1 or more hours.

For nation wide decision like school closure, perhaps the more stable 24 hours averaged out historical data can be used.

Besides, historical averaged 24 hrs and 3 hrs readings are always much lower at the start of the haze compare to spot reading. The difference can be as much as 30 or more psi. It is only when the haze continues to worsen for a few days that the NEA historical averaged data move closer to spot reading.

There has been some improvement to the NEA data due to public feedback. It was only in 2012 that PM2.5 particulate was incorporated into NEA 24 hrs psi reporting. For the 3 hrs psi, it was in 2014 that PM2.5 particulate was incorporated.

It has been observed over the years, the PM2.5 reading is normally much higher than PM10. Besides, PM2.5 can be inhaled into the lungs, making it much more hazardous than PM10 which can be filter by our nostril hair.  Thus, it is strange that NEA took so long to make the changes to adopt safety best practices though we have been hit by the haze for decades.

If other countries can provide their citizens with official real time reading, why is our govt so reluctant to do so all these years despite public feedback ?  We need it to make safe informed decision with regards to our daily activities when we are hit by the recurring haze year after year !

If govt wants us to refer to NEA data then provide us what we need - hourly reading. Don't chide the public for turning to other websites if NEA is reluctant to share real time raw information with us. Processed data can be unhealthy for our lungs.

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