Hey, welcome back to my blog! This week, I’m going to discuss how we measure air quality.

When we think about air quality, many might have the notion of “clear air is clean air”.  Clear air, however, is not indicative of “good” air quality.  Certain types of pollutants are invisible to the naked eyes, therefore it is erroneous to claim that the lack of visible pollutants suggests “good” air quality. There is actually a strict set of guidelines to meet before you can claim that your air quality is “good”.

In the 2005 World Health Organisation (WHO) Air Quality Guideline (AQG), the measurement of fine (PM_2.5) and coarse (PM₁₀) particulate matters, Ozone(O₃), Nitrogen Dioxide (NO₂), and Sulphur Dioxide (SO₂) are included into the measurement of air quality. Each of the pollutants has its own recommended level to adhere to since they have varying levels of toxicity.

Measuring air quality

Many forms of indexes that measure air quality exist around the world. Locally, Singapore uses the Pollutants Standard Index (PSI). The PSI takes the average of the 5 components measured, along with Carbon monoxide (CO) and uses this complicated equation to calculate the air quality before displaying it to us.

Interestingly, while CO is also featured in numerous indexes, it is not actually part of the WHO’s outdoor air quality guidelines. Considering that CO is quite a common by-product from car exhausts, perhaps the WHO should include it in its upcoming 2020 AQG?

Locally, our biggest threat to air quality is the haze generated by the occasional burning of forests from our neighbour, Indonesia. While searching for a way to check the PSI, I found that government websites for haze display 2 sets of information, the 24-hour average PSI and a more specific, 1-hour PM_2.5 reading. This made me wonder, why the specialised 1-hour PM_2.5 reading? Why are the remaining components not reported on an hourly basis?

Since the bulk of the pollutants from the haze are the particulate matters,  I think the remaining factors are perceived to have less significance and subsequently less priority. As such, there is a specialised section for an hourly report for the PM_2.5 reading.

This view seems to be a common one too.

In a survey I conducted, the majority of the people correctly identified that the particulate matters are measured in the PSI, but less than 50% identified the remaining factors. Maybe, they drew a stronger association for PM_2.5 reading since it is the more visible concern in haze incidents. While both sets of information seek to display the relative air quality, it is important to remember that the data they represent is not exactly the same!

I hope my content this week has helped you gain a clearer understanding of how air quality is measured, stay tuned for next week’s post!