Aiming to offer guidance in reducing the health impacts of air pollution, the World Health Organization (WHO) created its first air quality guideline (AQG) in 1987. These have since been updated, with the latest edition of WHO AQG for ambient air pollutants published in 2021. The WHO's guideline is widely referred to as the global authoritative guide for air pollution hazard and precautions.

What does the WHO’s guideline update mean? The update reflects the overwhelming body of research finding that an annual mean PM2.5 exposure of over 5 micrograms per cubic meter of air (µg/m3) poses a significant danger to human health – and the old standard isn’t safe enough. PM2.5 is particulate matter that measures 2.5 microns in diameter or less.

The WHO air quality guidelines for particulate matter is as follows:

Air pollutant WHO Exposure Guideline

PM2.5: 5 µg/m3 annual mean

15 µg/m3 24-hour mean

PM10: 15 µg/m3 annual mean

45 µg/m3 24-hour mean

While no amount of exposure to air pollution is completely safe, the WHO’s annual mean exposure guideline of 5 µg/m3 guideline is broadly referred to as the authoritative global guideline for PM2.5 exposure. This standard should be used to set government policies for reducing air pollution sources and to empower regulation enforcement in order to minimize negative health risks.

There are, however, several national air quality indexes used around the world. As an example, the U.S. Environmental Protection Agency’s (EPA) air quality index represents PM2.5 levels below 12 µg/m3 as lying within the "good" category. Note that this is more than twice the new WHO standards.

While the EPA’s definition for their “good” category air quality index meets current U.S. regulatory standards, they don’t rise to quality of the WHO’s more modern standards supported by the latest research and science. In other words, the U.S. EPA’s more dated standards for “good” are not good enough to protect human health.

The contrast makes it clear- the U.S. EPA’s dated standard is tied to a level of PM2.5 exposure that is significantly higher than the more current WHO standard. The air quality index must be updated to help save lives.

Here is the WHO guideline.

Air pollutant WHO Exposure Guideline

PM2.5: 5 µg/m3 annual mean

15 µg/m³ 24-hour mean

PM10: 15 µg/m3 annual mean

45 µg/m3 24-hour mean

See the U.S. air quality index for PM2.5 concentrations below for a clear comparison between the U.S. AQI and the WHO guideline. Again, note the significantly higher threshold in the “good” category listed below:

Also see this chart for reference to PM2.5, AQI, and additional pollutants in the revised WHO guideline:

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