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Modeling Tales of Horror


With Halloween upon us I thought it would be fun to offer up a few “scary” modeling tales that are likely to keep the regulated community awake at night. In one tale we tell the story of a new requirement for modeling; like The Blob from the 1958 sci-fi/horror classic, we should be afraid that it will spread across the country and consume all in its path. The other story is one of a looming threat on the horizon; like the Martians at the start of H.G. Wells’ “War of the Worlds,” this threat is slowly and surely drawing its plans against the world of the modeled—and make no mistake, it is coming for us.


So with that, cue the dramatic music and read on…if you dare…


The Blob:

Short-term NAAQS modeling for even minor permitting efforts—and eventually for existing facilities


Starting this past summer, the Oregon Department of Environmental Quality (DEQ) is now requiring short-term NAAQS modeling (1-hr SO2, 1-hr NO2, and 24-hr PM2.5) for sources undergoing Simple and Standard air contaminant discharge permitting. DEQ’s rationale is that the NAAQS Significant Emission Rates were developed based on annual emissions and, because emission rates can vary over the course of a year, relying on annual average emissions can obscure a high short-term peak in emissions—which possibly could lead to NAAQS exceedances. DEQ wants to address this “loophole” with short-term NAAQS modeling.


Requiring modeling of sources getting a new permit is not terribly new, although the threshold for triggering modeling may be lower in this case. But keeping with our Halloween theme, the scary part of DEQ’s new policy is that it also states that while existing sources don’t have to do anything now that will not always be the case—the DEQ is working on a plan to start requiring existing facilities to do this kind of modeling. So yes, there’s a chance that if you’re an existing facility in Oregon that has never had to model before you’ll soon be required to conduct the most challenging modeling of all, short-term modeling.


It crawls…it creeps…it eats you alive! (The Blob)


History has told us that air quality regulations aren’t static, and they don’t ease up over time—they get more stringent. Based on that I would expect that other states will jump on this bandwagon and that, in the coming years, we’ll start seeing other states pull into modeling facilities that aren’t even undergoing a permitting exercise. They'll just be sitting there and the Blob will get them.


Slowly and surely drawing its plans against the world of the modeled:

The likely lowering of the PM2.5 Annual NAAQS


The Clean Air Act requires that every five years the EPA review its NAAQS to make sure they adequately protect human health and the environment. The Trump administration conducted such a review of the PM10 and PM2.5 NAAQS and announced in April 2020 that they would be retained without any modification.


When the Biden administration took office they revisited this decision, and earlier this month EPA published its “Policy Assessment for Reconsideration of the NAAQS for PM, External Review Draft.” In that document EPA indicated they were leaning toward reducing the PM2.5 annual NAAQS from the current 12 µg/m3 to 10 µg/m3 or possibly as low as 8 µg/m3.


Such an extraordinary effect in unmanning me it had that I ran weeping silently as a child might do. (War of the Worlds)


Most think that the PM2.5 annual NAAQS will end up at 10 µg/m3, but there’s reason to fear a decrease to 8 µg/m3 because that’s consistent with the definition of an “overburdened census tract” in the CLEAN Future Act as proposed in March of this year. Even if the NAAQS is lowered only to 10 µg/m3 that would immediately put dozens of areas in the US into nonattainment for PM2.5, and those that would still be in attainment would have even less room for modeled annual PM2.5 impacts than they do now. Even with the NAAQS currently at 12 µg/m3 often annual PM2.5 modeling is the most challenging to conduct because the ambient background is so high relative to the standard. So clearly if it gets tightened to 10 µg/m3 it’s going to be even more difficult to demonstrate compliance.


With a new modeling horror seemingly around every corner sometimes those of us in the modeled community can feel like the artilleryman in “War of the Worlds” when he says “this isn’t a war…any more than there’s war between man and ants.” But take heart, because even the seemingly unstoppable Martians eventually “were destroyed and humanity was saved by the littlest things which God and His wisdom had put upon this Earth.”


Wait—does that make us modelers the littlest things God has put upon this Earth?

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