What are the WHO guidelines?

Based on the existing scientific evidence, in September 2021 the World Health Organization (WHO) set new recommended limits for concentration of air pollutants. According to these guidelines, outdoor concentrations of PM_2.5 should not exceed an annual mean value of 5 µg/m³. The outdoor recommended limit for NO₂ concentrations is 10 µg/m³.

Although these guidelines are considered the gold standard for the protection of human health, they are just recommendations and not mandatory.

The original study that led to our Air Pollution Rankings was based on the previous WHO Global Air Quality Guidelines, which had been published in 2005 and set less ambitious reference levels (10 µg/m³ for PM_2.5 and 40 µg/m³ for NO₂. The current version of the website includes the number of annual premature deaths that could be avoided meeting both the new and the former WHO guidelines.

For more information, visit https://apps.who.int/iris/handle/10665/345329