Singapore PSI and PM2.5 AQI: Why is there a difference between the two readings?

Posted on June 25th 2013
ແບ່ງປັນ: aqicn.org/faq/2013-06-25/singapore-psi-and-pm25-aqi-why-is-there-a-difference-between-the-two-readings/lo/
Please note that this article was orginally written in June 2013.
In April 2014, the Singapore NEA has updated the PSI calculation to also include PM2.5. http://www.nea.gov.sg/anti-pollution-radiation-protection/air-pollution-control/psi

With the recent Southeast Asia Smog from Indonesia affecting Singapore and now Malaysia, we got many questions about why there is a difference between the data which can be read from Singapore NEA website (nea.gov.sg) and the World Air Quality Index project Singapore webpage.

For instance, here is what can be read today in NEA website:


For some historical reason, Singapore is using the PSI (Pollutant Standard Index) to evaluate the Air Quality. In the image above, number 1 corresponds to the PM10 value that is used for the PSI evalation. The value 67(/59) can be read as 67 μg/m3, corresponding to a PSI of 59. The PSI is evaluated as the maximum of the individual PSI for each of the pollutants: PM10, SO2, NO2, O3 (Ozone) and CO2.

PSI(Singapore-North) = max( PSIPM10-based, ... PSIO3-based )= max (59, ..., 77) = 77

This said, the interesting thing is that, in this same table, the PM2.5 data is also provided in the last column (see 3). This data is provided in μg/m3 only (see 2), and there is no conversion to something like the PSI (i.e. a conversion from the PM2.5 mass to a Pollution or Quality Index). This conversion however exists, and is defined by the US Environmental Protection Agency. The easiest way to do the conversion is to use the online calculator, available at airnow.gov:


If you select the PM2.5 (1), then enter the mass concentration of 48 (2), can click on Calculate, you will obtain the AQI of 132 (3). So, based on the PM2.5 AQI conversion, the PSI that is used for Singapore could be extended (let's call it PSI++) to also take into account the PM2.5 information. In which case, the PSI++ would be the maximum of the regular PSI (based on PM10 only) and the PM2.5 AQI:

PSI++ = max( PSI, AQIPM.25 ) = max( 77, 132 ) = 132

This PSI++, that is commonly referred as AQI (or Air Quality Index), is what is being used on the the World Air Quality Index project, for all the cities (provided PM2.5 is available for the city). And this explains why the values are different between the NEA website and the World Air Quality Index project.

Note: With the PSI update from April 2014, the only remaining difference is that the World Air Quality Index project is using a 1-hour PM2.5 reading (following the instantcast) while Singpore PSI is based on the 3 hours average.

Moreover, when doing the convertion, make sure you use the 1-hour reading for the PM2.5 concentration rather than the 24-hours averaged value, as shown on the below image:


http://www.haze.gov.sg/haze-updates/pollutant-concentrations/type/PM25-1Hr


If you want to know more about PM10 vs PM2.5, and especially why PM10 is still used, please check the faq entry about why is PM2.5 often higher than PM10? Is PM10 still a relevant measure?


--

Note: This article is part of a series on Worldwide Air Quality scales.

For more information about specific countries or continent, please refer to those articles:
Thailand and Malysia
-
India
-
China
-
Hong Kong / Canada (Air Quality Health Index)
-
South America
-
Australia
-
Quebec and Montreal
-
Singapore
-
Poland
-
Indonesia
.

For information about the 24 hours averaging used or Ozone and Particulate Matter (PM2.5), please refer to those two articles: Ground Ozone Index - PM2.5 Instant Cast

Click here to see all the FAQ entries
  • AQI Scale: What do the colors and numbers mean?
  • Using Statistical Distances for Real-time Sensor Networks Validation
  • Nitrogen Dioxyde (NO2) in our atmosphere
  • ກ່ຽວກັບການວັດແທກຄຸນນະພາບອາກາດ ແລະມົນລະພິດ:

    ກ່ຽວກັບລະດັບຄຸນນະພາບອາກາດ

    -ດັດຊະນີຄຸນນະພາບອາກາດ (AQI) ຄ່າLevels of Health Concern
    0 - 50ດີຄຸນນະພາບທາງອາກາດຖືກພິຈາລະນາເປັນທີ່ພໍໃຈ, ແລະມົນລະພິດທາງອາກາດກໍ່ມີຄວາມສ່ຽງຫນ້ອຍຫຼືບໍ່ມີຄວາມສ່ຽງ
    51 -100ປານກາງຄຸນນະພາບທາງອາກາດແມ່ນການຮັບຮອງ; ຢ່າງໃດກໍ່ຕາມ, ສໍາລັບບາງມົນລະພິດອາດມີຄວາມກັງວົນກ່ຽວກັບສຸຂະພາບໃນລະດັບປານກາງສໍາລັບຈໍານວນຜູ້ທີ່ມີຄວາມເຄັ່ງຕຶງທີ່ຜິດປົກກະຕິກັບການມົນລະພິດທາງອາກາດ.
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    300+ອັນຕະລາຍເຕືອນດ້ານສຸຂະພາບ: ທຸກໆຄົນອາດຈະມີຜົນກະທົບທາງສຸຂະພາບທີ່ຮ້າຍແຮງກວ່າເກົ່າ

    ເພື່ອຮູ້ເພີ່ມເຕີມກ່ຽວກັບຄຸນນະພາບອາກາດ ແລະມົນລະພິດ, ໃຫ້ກວດເບິ່ງ ຫົວຂໍ້ຄຸນນະພາບອາກາດຂອງ wikipedia ຫຼື ຄູ່ມື airnow ກ່ຽວກັບຄຸນນະພາບອາກາດ ແລະສຸຂະພາບຂອງເຈົ້າ .

    ສໍາລັບຄໍາແນະນໍາດ້ານສຸຂະພາບທີ່ເປັນປະໂຫຍດຫຼາຍຂອງທ່ານຫມໍປັກກິ່ງ Richard Saint Cyr MD, ກວດເບິ່ງ blog www.myhealthbeijing.com .


    ແຈ້ງການນໍາໃຊ້: ຂໍ້ມູນຄຸນນະພາບອາກາດທັງຫມົດແມ່ນບໍ່ຖືກຕ້ອງໃນເວລາທີ່ພິມເຜີຍແຜ່, ແລະເນື່ອງຈາກການຮັບປະກັນຄຸນນະພາບຂອງຂໍ້ມູນເຫຼົ່ານີ້ອາດຈະຖືກປັບປຸງ, ໂດຍບໍ່ມີຂໍ້ສັງເກດ, ໃນທຸກເວລາ. ໂຄງການດັດຊະນີທາງອາກາດໂລກໄດ້ໃຊ້ທັກສະແລະການດູແລທີ່ສົມເຫດສົມຜົນທັງຫມົດໃນການລວບລວມເນື້ອໃນຂອງຂໍ້ມູນນີ້ແລະພາຍໃຕ້ສະພາບການໃດກໍ່ຕາມທີມງານຂອງໂຄງການໂລກຂອງອາກາດທາງໂລກຫຼືຕົວແທນຂອງມັນຈະຮັບຜິດຊອບໃນສັນຍາ, ຄວາມເສຍຫາຍຫຼືຄວາມເສຍຫາຍໃດໆ, ເກີດຂື້ນໂດຍກົງຫຼືໂດຍທາງອ້ອມຈາກການສະຫນອງຂໍ້ມູນນີ້.



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