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The hour of doom is upon us: the new PM2.5 Annual NAAQS is here



(As a preface, I concede “doom” is perhaps a bit too strong, but I’m just trying to have a little fun with some news that is definitely not good for the regulated community…)


In J. R. R. Tolkien’s “The Return of the King” (the third installment in his masterpiece trilogy “Lord of the Rings”) there is a scene where the evil armies of the Dark Lord Sauron capture Osgiliath, a fort that serves as the last line of defense between Mordor (the realm of Sauron) and Minas Tirith (the capital city in the Kingdom of Gondor).


Osgiliath’s forces flee across Pelennor Fields and retreat to Minas Tirith. When they arrive, their captain exclaims “They broke our defenses. They’ve taken the bridge and the West bank. Battalions of orcs are crossing the river.” Another soldier cries out “It is as Lord Denethor predicted! Long has he foreseen this doom!”


Well, my modeling friends, I feel today as if we are the forces who tried very hard to defend Osgiliath, only to see it fall. Despite a wave of resistance and comments to the contrary, EPA has finally broken through the defenses and put out the new PM2.5 Annual National Ambient Air Quality Standard (NAAQS). It is indeed as we predicted, and indeed long have we foreseen this doom.


Today EPA has announced that the new PM2.5 Annual NAAQS is 9 µg/m3, down from the previous 12 µg/m3 (for those of you scoring at home, that’s a 25% reduction). The official Final Rule can be found here: https://www.epa.gov/system/files/documents/2024-02/pm-naaqs-final-frn-pre-publication.pdf


For some brief history, during the Trump Administration EPA examined the NAAQS and determined that they didn’t need to be changed. However, the Biden Administration’s EPA reversed that and announced they were considering lowering the PM2.5 NAAQS . That’s been brewing for the past couple of years, and now we have a much lower PM2.5 Annual NAAQS.


The rule is effective 60 days from publication in the Federal Register, so we’re probably looking at this going into effect sometime in the spring of this year.


What does this mean for the regulated community? Well, permitting just got a lot more difficult. Not so much because of the modeled impacts of annual PM2.5 from a facility trying to get a permit, but more likely from the background concentrations that you will need to add to the modeled concentrations when doing a cumulative NAAQS analysis. Much of the country already has annual PM2.5 background values close to this new NAAQS, and a large amount of the country west of the Rocky Mountains is now nonattainment for annual PM2.5. In other words, there’s very little room to fit under the Annual PM2.5 NAAQS any more, and in some places there isn’t any.


So if you’re going for a permit you now need to pay very close attention to your annual PM2.5 emissions/predicted concentrations. Can you keep your project small enough to avoid PSD? If not, can you stay below the Significant Impact Level for annual PM2.5 to avoid a cumulative NAAQS demonstration? If you must do a cumulative NAAQS demonstration, can you find a monitor that gives enough “buffer” where it’s possible to meet the NAAQS? There are methods available to refine/reduce the background concentration, do you need to go down that path?


If you’re planning a PSD project in the future, proactively take a look at annual PM2.5 background concentrations in your area. If the monitor data available won’t allow you to meet the NAAQS, perhaps consider installing your own PM2.5 monitor to get some lower concentrations that you can use?


So, as we fall back to Minas Tirith and regroup, if you’re in the environmental department of an industrial facility it’s important that your management know that permitting just got tougher. Planning for the future is now more important than ever. It’s time to get a handle on the annual PM2.5 background concentrations you have at your disposal, and if you don’t already know what your modeled annual PM2.5 impacts look like, it’s probably a good idea to do some modeling so you can know not only where you are but where, if anyplace, you might be able to go in the future.


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