The WHO’s guideline limit for PM2.5 is 5 micrograms. But research shows reducing PM2.5 levels under 5 micrograms has significant health benefits and reduces mortality. What is the safe limit of PM2.5?

Is the WHO PM2.5 Guideline of 5 Micrograms Safe?

The WHO PM2.5 guideline is not intended to represent the safe limit of PM2.5. Rather, it is intended to provide targets for policymakers. In fact, the WHO itself stated that there are negative health effects below the limit.

The risk for various outcomes has been shown to increase with exposure and there is little evidence to suggest a threshold below which no adverse health effects would be anticipated.

WHO Global update 2005

In addition, since the release of the WHO’s first guidelines in 1987, the PM2.5 guideline has been lowered multiple times, from 15 to 10 micrograms, and again from 10 to 5 micrograms. This pattern is very similar to how the CDC’s lead standards have changed over the decades:

Read More: The WHO Updates PM2.5 Guidelines in 2021

Similar to Lead, There is No Safe Level of PM2.5

A new study tried to find the answer to “What is the safe limit of PM2.5?”. They studied 7.1 million adults in one of the world’s lowest PM2.5 environments. The lowest observed PM2.5 concentration of 2.5 micrograms was used as the base level.

As shown in the graph above, even slight increases in PM2.5 from the base level have significant increases in mortality. This shows that even in areas with the “best air quality in the world“, lowering PM2.5 further can have significant health benefits and save lives.

Lowering levels below 2.5 micrograms would likely show a similar significant reduction in mortality. There are simply not enough places with such low levels to gather data from.