WHO 2021 Air Quality Guidelines – My Take!

On 22nd September 2021, the World Health Organization released the so long-awaited update of the Air Quality Guidelines (AQGs). They are bold and ambitious but will governments adopt them?

Let’s see how the updated AQGs compare to the old ones, which were released in 2005. The classical pollutants (Particulate Matter PM2.5/10, and NO2) have been reduced significantly. They have introduced additional AQG levels, such as for peak season Ozone (O3), 24-hour averaging time for Nitrogen Dioxide (NO2), and Carbon Monoxide (CO). On the contrary, they have increased the Sulfur Dioxide (SO2) levels from 20 μg/m3 to 40 μg/m3.

Let’s address the reason they increased the concentration for SO2. Today scientists use new methods for evidence synthesis and guideline development than 15 years ago and this is the main reason according to the spoken person during the press conference. Personally, I think there was no harm in keeping SO2 concentrations as low as before even if it is “safe” at 40 μg/m3. Ports and industrial sites around the world have tried hard to keep SO2 levels below 20 μg/m3 for 15 years.

I was asked a lot by my followers about the absence of ultrafine particles (UFPs) and PM1 inside the 2021 AQGs. WHO offers new good practice statements on the management of certain types of PM (i.e. black carbon/elemental carbon, ultrafine particles, and particles originating from sand and dust storms). Also, it doesn’t make lots of sense to offer mass concentration (μg/m3) guideline values for UFPs and PM1 as the size of the particles is so small that mass concentration values don’t reflect the real impact those nanoparticles have on human health. Experts debate how can we express those values better and we conclude that a particle count number divided by a factor in order to make values more manageable by our human brains make sense.

A quick example: 31058 particles of PC0.1 equal to 0.02 μg/m3. However, 209 particles of PC2.5 are equivalent to 2.95 μg/m3. Do you get it? It is unfair to measure nanoparticles in mass concentration.

Something completely redone inside the 2021 AQGs was the introduction of the Interim target. Interim targets (with 4 levels) serve as incremental steps in the progressive reduction of air pollution towards the air quality guideline levels and are intended for use in areas where air pollution is high. In other words, they are air pollutant levels that are higher than the air quality guideline levels, but which authorities in highly polluted areas can use to develop pollution reduction policies that are achievable within realistic time frames.

At first, I was skeptical about the interim targets because I was worried that governments will choose a level (1/2/3/4) that fits their agenda and will forget that they need to improve air quality over time. Even if that’s the case, they will take a step towards studying the AQGs which means that they will become aware of air pollution, something that currently most politicians aren’t. So I see the interim targets as an educational tool to help policymakers around the world understand the concept of air pollution. Moreover, we could compare the interim targets to a gamification strategy nowadays smartphone games have embedded. Try to become better over time by achieving new goals.

Countries like India or Pakistan, where poor air quality is a constant problem all year round for a variety of reasons, will begin from level 1 towards level 4 and finally meet the AQGs. European countries aren’t any better, take as an example Greece. Greece has to begin with an aim to achieve an interim target level 3 (at least) and work towards the AQGs.


All in all, I am very excited about the new guidelines. However, governments need to adopt them as soon as possible and work towards a future without air pollution. A broadly monitoring of the air quality within cities is also mandatory to ensure the right of clean air for all dwellers (poor & rich). Moreover, the EU has to step up today and take advantage of the 2021 AQGs if they want to secure a sustainable and healthy future. Additionally, the AQGs will help in managing the climate crisis as air pollution and climate change are intertwined problems.

Download for free the complete 300-page WHO global air quality guidelines book here.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s