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WHO announces new Air Quality Guidelines--foreshadowing of what's to come in the US?

foreshadowing: noun, an indication of something that will happen in the future, often used as a literary device to hint at or allude to future plot developments

Yesterday, on September 22, 2021 the World Health Organization (WHO) announced new Air Quality Guidelines (AQGs) for a host of pollutants that are called criteria pollutants in the United States. Many of these AQGs are far more stringent than corresponding National Ambient Air Quality Standards (NAAQS); coupled with the announcement by the U.S. Environmental Protection Agency (EPA) earlier this summer that they will be re-examining the PM2.5 NAAQS, this creates even more reason for industry in the United States to be on the watch for tightening air quality standards.

The WHO’s AQGs are not legally binding standards but are designed to provide WHO Member States with guidelines they can use to inform air quality regulations. In addition to being used by many countries in the world they are implemented by global financial institutions when addressing the environmental impacts of their lending activities (through the Equator Principles).

The last time the WHO published AQGs was in 2006. Since that time the WHO states that there has been an increase in evidence of the deleterious effects of air pollution at much lower levels than previously studied, and thus these revised AQGs.

The table below presents the new AQGs, along with the corresponding NAAQS (if applicable).

As you can see, some of these new AQGs are much more stringent than the corresponding NAAQS; for example, the annual NO2 AQG is one-tenth of the annual NO2 NAAQS.

Perhaps most important is the aggressive stance the WHO is taking with regards to particulate matter. The new AQGs for both PM2.5 and PM10 are less than half of the corresponding NAAQS. For many parts of the world the annual PM2.5 AQG will be unattainable for the foreseeable future, because even without any additional industrial development many countries already exceed annual PM2.5 levels of 5 µg/m3.

(As a reference point, there are roughly 500 locations in the United States—a country with much cleaner air than most of the world—with annual PM2.5 design values greater than 5 µg/m3.)

In June of this year the EPA announced that it was going to re-visit the Trump Administration’s decision to retain the annual and 24-hr PM2.5 NAAQS. Some think the annual PM2.5 NAAQS may be tightened to 10 µg/m3 or perhaps 8 µg/m3; the 8 µg/m3 level has been called for under the proposed CLEAN Future Act. With the WHO now advocating an annual PM2.5 AQG of 5 µg/m3 does this give more credence to the Biden Administration’s interest in possibly lowering the PM2.5 NAAQS? Time will tell but one thing is for certain—the WHO has just made modeling for PM2.5 far more challenging for much of the world than it has been in the past. Whether this will turn out to be foreshadowing of a more restrictive PM2.5 NAAQS in the US, we will have to wait and see.

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