Overview of Hong Kong's Air Quality Health Index

Posted on June 3rd 2015
Share: aqicn.org/faq/2015-06-03/overview-of-hong-kongs-air-quality-health-index

Note: This the fith article of series on 'Worldwide Air Quality Scales'.

It is already a long time since the Hong Kong EPA has updated its Air Quality Index standard from the traditional Air Pollution Index to the so called Air Quality Health Index (AQHI), but we never got a change until now to have a deeper look at it, which we will do in this article.

The Hong Kong EPA has actually done an excellent work at explaining how the AQHI is defined, and the information one needs to understand the AQHI is available from their website. The most obvious simplification is the change of the traditional 0-500 index into a new simplifed 0-10+ range, sub-divded in five health risk categories, as shown below:

LOW MODERATE HIGH VERY HIGH SERIOUS
1 2 3 4 5 6 7 8 9 10 10+

But there is actually much more than a range simplification: the new AQHI is also introducing the very clever concept of Added Health Risk (%AR), which was originally defined, in 2007, by a team of four partners from South Africa, and first used in Canada.

Unlike the traditional AQI for which the AQI is defined as the maximum of the Individual AQIs, the AQH is defining the overall Augmented Risk (AR) as the sum of the Individual pollutants Augmented risk (IAR). The idea is, for instance, that if both ozone (O3) and particule matter (PM2.5) levels are high, then the risk for health is likely twice as big as if only particule matter level was be high. In the case of the traditional AQI scale, the AQI does not taken into account the multiple pollutant situation, i.e. the AQI is only defined as the maximum level from all pollutants.
AQHI Augmented Risk = IAR ( NO2 ) + IAR ( SO2) + IAR ( O3 ) + max( IAR ( PM2.5 ), IAR ( PM10 ) )

Traditional AQI = max( IAQI ( PM2.5 ), IAQI ( PM10 ), IAQI ( O3 ), IAQI ( NO2 ), IAQI ( SO2 ) )
The Individual pollutants Augmented risk (IAR) are based on epidemiological studies using Hong Kong's health statistics and air pollution data. They work by defining a correlation cooeficient between pollutant level and relative risks, which are measured by hospital admissions. But because graphs are quite often much easier to understand, the IAR breakpoints are plotted on the graph below:

Few interesting points are worth noticing: First this is yet another evidence of epidimiologic correlation between PM10 and PM2.5 - meaning that for countries where only PM10 is available, it it possible to deduct a PM2.5 like AQI - like we explained in this article.

Second, the highest augmented risk for equivalent concentration is the Ozone. Because the way the epidemiologicial study is done, it most likely reflects the risk due to a prolonged exposure. In other words, if compared, then it should be done with the 8 hours Ozone standard rather than the hourly standard. That can actually be a problem since we have recently updated our system to the use hourly instant cast Ozone AQI as we do believe that was is important for the citizens as a health decision is the actual concentrations, and not the one from 8 hours ago.

Last, in case one pollutant is not available, then the calculation is not possible anymore. For this reason, the AQHI is using a 3 hours rolling average, so that, when a pollutant is missing, it can be estimated as the average as the previous 2 hours. Moreover, if there is more than one hour of missing pollutnat data, then the AQHI is not reported.
oOo

So, now that the concept behind the AQHI is understood, the last step is to have a practipal comparisons of the reported values using the traditional AQI scale and the new AQHI scale, which is done in the example below using the past 15 days data from Shanghai Jing'an station (静安监测站).

For the sake of a consistent visual comparison, we introduce an intermediate color for the moderate (3-6) levels, as following:
0-3
3-4.5
4.5-6
6
7-10
10+ . The visual comparison result speaks for itself, with AQHI reporting higher levels (
) than traditional AQI (
) when several pollutants are high at the same time (most of the time Ozone and PM2.5), and AQHI reporting low
when only one pollutant is high (happens when only PM2.5 is moderate
, but all other pollutants are low
). That means that no scale is better than any other one, but each scale is having their own strong points are reporting specific pollution event.

HK AQHI Standard

US AQI Standard

US Individual AQI



oOo

As the conclusion, what is the most important is to remember as that each scale has its own specificity, and the most important is to keep the diversity in the scales: We are starting to believe that having only one unique scale might not be the right solution, and we are now working on a global solution which will allow users the select the scale which best fits their needs.


Click here to see all the FAQ entries
  • Nitrogen Dioxyde (NO2) in our atmosphere
  • Ozone AQI Scale update
  • Kriging Interpolation

  • Read or publish comments (they rely on Disqus)

    À propos de la qualité de l'air et des mesures de la pollution atmosphérique :

    À propos des niveaux de qualité de l'air

    IQANiveau de pollution de l'air Impact sur la santé
    0 - 50BonLa qualité de l'air est jugée satisfaisante, et la pollution de l'air pose peu ou pas de risque.
    51 -100ModéréLa qualité de l'air est acceptable. Cependant, pour certains polluants, il peut y avoir un risque sur la santé pour un très petit nombre de personnes inhabituellement sensibles à la pollution atmosphérique.
    101-150Mauvais pour les groupes sensiblesLa qualité de l'air est acceptable; Cependant, pour certains polluants, il peut y avoir un problème de santé modérée pour un très petit nombre de personnes qui sont particulièrement sensibles à la pollution de l'air.
    151-200MauvaisTout le monde peut commencer à ressentir des effets sur la santé; les membres des groupes sensibles peuvent ressentir des effets de santé plus graves.
    201-300Très mauvaisAvertissements de santé de conditions d'urgence. Toute la population est plus susceptible d'être affecté.
    300+DangereuxAlerte de santé: tout le monde peut ressentir des effets de santé plus graves.

    Pour en savoir plus sur la qualité de l'air, consultez le sujet Qualité de l'air sur Wikipedia ou le guide AirNow de la qualité de l'air et de votre santé .

    Pour des conseils de santé très utiles du Dr. Richard Saint Cyr, consultez le blog myhealthbeijing.com.


    Notice d'utilisation: Toutes les données sur la qualité de l'air ne sont pas validées au moment de la publication et, pour des raisons d'assurance de la qualité, ces données peuvent être modifiées à tout moment et sans préavis. Le projet Indice de la qualité de l'air dans le monde a exercé toutes les compétences et l'attention réalisables dans la compilation du contenu de ces informations. Indice de la qualité de l’air dans le monde , l’équipe de projet ou ses agents ne peuvent être tenus responsables, contractuellement, judiciairement ou autrement, de toute perte, blessure ou préjudice résultant directement ou indirectement de la fourniture de ces données.



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