BetterIn September 2021, the World Health Organization published new global air quality guidelines and lowered almost every threshold in them.
Nothing had happened to the air. Something had happened to the evidence.
WHO “adjusted almost all the AQGs levels downwards”because the evidence shows harm “at even lower concentrations than previously understood”.
The previous edition dated from 2005. Sixteen years of accumulated studies did not change what was in the air; they changed the verdict on it.
Air that counted as acceptable in 2005 does not count as acceptable now. The same air. A different answer.
ThresholdsWhat a threshold actually is
A guideline level reads like a property of the air. It is not. It is a statement about what is known.
WHO describes the process without drama: since the 2005 edition “there has been a marked increase of evidence that shows how air pollution affects different aspects of health”, and so, “after a systematic review of the accumulated evidence”, the levels came down.
Why this is worth understanding. When a limit is lowered, it is easy to read it as an admission that the old one was a lie, or as goalposts being moved. It is neither. It is what a threshold does when the studies underneath it accumulate, and a body that never moved its thresholds would be telling you it had stopped looking.
RankingWhere it sits among health risks
The 2021 release does something the earlier fact sheets do not: it says what this risk is comparable to.
And the comparison, in WHO's own words: the burden of disease attributable to air pollution is “on a par with other major global health risks such as unhealthy diet and tobacco smoking”. Two risks that come with campaigns, warning labels and taxes, and one that mostly does not.
And the list of effects is still growing. Beyond heart disease and stroke, WHO notes that “evidence is also emerging of other effects such as diabetes and neurodegenerative conditions”. Emerging is the operative word, it is not established, and WHO does not present it as such. We keep the hedge because the source did.
ParticlesWhy the smallest particles matter most
This is where the whole card closes on itself. The first article found that most deaths are cardiovascular. Here is the physical reason.
“PM₂.₅ and PM₁₀ are capable of penetrating deep into the lungs but PM₂.₅ can even enter the bloodstream, primarily resulting in cardiovascular and respiratory impacts, and affecting also other organs.”
Their source is named too: “fuel combustion in different sectors, including transport, energy, households, industry, and from agriculture.”
Lungs are the door. The bloodstream is the corridor. The heart is where the counting happens.
Note that households appear on that list of sectors, between energy and industry. The indoor half of this card is not a separate subject filed elsewhere, WHO puts it in the same sentence as transport and agriculture, and says the guidelines apply to indoor and outdoor environments alike.
The last wordOne sentence to end on
The release ends on a quotation that is worth taking literally, because it is unusually free of hedging for an institutional document.
“We know the magnitude of the problem and we know how to solve it. These updated guidelines give policy-makers solid evidence and the necessary tool to tackle this long-term health burden.”
Dr Hans Henri P. Kluge, WHO Regional Director for Europe
The same paragraph adds the part that is not solved: “millions of people continue to die prematurely, often affecting the most vulnerable and marginalized populations.”
Which is the honest place to leave a subject like this one, and this whole set of articles. Almost none of what has been counted here is unknown. The scale is measured, the causes are named, the tools are published and mostly unglamorous. What separates the measurement from the result is not a discovery.
QuestionsFrequently asked questions
What did WHO change in 2021?
It “adjusted almost all the AQGs levels downwards”, after a systematic review of the evidence accumulated since the previous edition, which dated from 2005.
Why lower them?
Because the evidence shows damage “at even lower concentrations than previously understood”. What changed between 2005 and 2021 is not the air, it is what is known about its effects.
Which pollutants are covered?
Six: particulate matter (PM10 and PM2.5), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. WHO specifies that the guidelines apply “to both outdoor and indoor environments globally”.
What is the disease burden comparable to?
WHO writes it: the burden of disease attributable to air pollution is “on a par with other major global health risks such as unhealthy diet and tobacco smoking”.
Is air pollution carcinogenic?
WHO's International Agency for Research on Cancer classified outdoor air pollution and particulate matter as carcinogenic in 2013. That classification is from 2013, not 2021.
Do we know how to fix it?
WHO's Regional Director for Europe puts it in one sentence: “We know the magnitude of the problem and we know how to solve it.” What is missing, in his account, is not evidence: the guidelines exist to give policy-makers “the necessary tool”.
Read nextRelated
Sources
- New WHO Global Air Quality Guidelines, World Health Organization, 22 September 2021
- Ambient (outdoor) air pollution, World Health Organization, updated 24 October 2024
About this article. General and educational information, not medical advice. The quotations come from the World Health Organization press release of 22 September 2021 presenting the global air quality guidelines, consulted in its French and English versions. The seven million deaths estimate is the one in that 2021 release; the more recent fact sheets give 4.2 million for outdoor (2019), 2.9 million for household (2021), and 6.7 million for the combined effects. These figures neither add up nor replace one another: each carries its own scope and year.
Spotted an error or an out-of-date figure? Write to us: we will correct it and re-date the article. Our texts are written with the help of artificial intelligence and checked against official sources before publication, but a figure or a definition can change without us catching it. If anything here does not match what an official body tells you, they are right.