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 PM_2.5. http://www.nea.gov.sg/anti-pollution-radiation-protection/air-pollution-control/psi

Sa nedavnim smogom iz Jugoistočne Azije iz Indonezije koji pogađa Singapur i sada Maleziju , dobili smo mnoga pitanja o tome zašto postoji razlika između podataka koji se mogu pročitati sa Singapurske NEA web stranice ( nea.gov.sg ) i projekta Svjetskog indeksa kvalitete zraka u Singapuru web stranica .

Na primjer, evo šta se danas može pročitati na web stranici NEA:

Iz nekog istorijskog razloga, Singapur koristi PSI ( standardni indeks zagađivača ) za procjenu kvaliteta zraka. Na gornjoj slici, broj 1 odgovara vrijednosti PM10 koja se koristi za PSI procjenu. Vrijednost 67(/59) može se očitati kao 67 μg/m3, što odgovara PSI od 59. PSI se procjenjuje kao maksimum pojedinačnog PSI za svaki od zagađivača: PM ₁₀ , SO ₂ , NO ₂ , O ₃ (ozon) i CO ₂ .

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

S tim u vezi, zanimljiva stvar je da su u istoj tabeli podaci o PM2,5 također dati u posljednjoj koloni (vidi 3). Ovi podaci su dati samo u μg/m3 (vidi 2), i nema konverzije u nešto poput PSI (tj. konverzija iz mase PM2,5 u indeks zagađenja ili kvaliteta). Ova konverzija, međutim, postoji i definirana je od strane Američke agencije za zaštitu okoliša . Najlakši način da izvršite konverziju je korištenje online kalkulatora, dostupnog na 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 PM_2.5 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?


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