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50 Shades of Green

Issue 2 and Volume 117.


If you relied solely on EPA’s press releases to understand the impacts of new regulations and revised National Ambient Air Quality Standards (NAAQS), you would view the environment as yes or no, good or bad, black or white. But the reality of clean air compliance is much more complicated and shaded.

In December 2012, EPA “strengthened” the Pm2.5 annual National Ambient Air Quality Standard (NAAQS) from 15 µg/m3 to 12 µg/m3. EPA’s data shows 66 counties do not currently meet the 12 µg/m3 standard, but final non-attainment designations don’t have to be made until December 2014. By reducing this standard, EPA expects “fewer than 10 counties, out of the more than 3,000 counties in the United States, will need to consider any local actions to reduce fine particle pollution in order to meet the new standard by 2020,” which is the attainment goal date. These unfortunate counties are, of course, located in southern California, where poor air quality is a constant problem.

EPA’s projections mean that from 2012 to 2020, 56 counties have to improve their air quality to better than 12 µg/m3 of Pm2.5 on an annual basis. EPA is relying largely on reductions in particulate matter (PM) resulting from other EPA rules, such as the Utility maximum achievable control technology (MACT) rule, Boiler MACT rule and the reciprocating internal combustion engine (RICE) MACT rule. They expect additional benefits from the final incarnation of the Clean Air Interstate Rule (CAIR). EPA would lead you to think that only southern California need worry about their Pm2.5 emissions and this lowered standard, and that is misleading.

There’s more to the story than just that air quality above 12 µg/m3 is bad and below is good. Except for very small projects, a new facility applying for a construction permit or an existing facility applying for a modification must demonstrate that the new emissions do not cause or contribute to an exceedance of the NAAQS. A dispersion model is used to simulate the new emissions and determine the ground level concentration of pollution. The result is then added to the impact from nearby sources plus a background concentration. This background concentration is the same value that is compared to the 12 µg/m3 standard. Therefore, if the county is in compliance with the new 12 µg/m3 standard with a monitored value of 11.5 µg/m3, there is only 0.5 µg/m3 left for both the new emissions plus the existing nearby sources.

Figure 1 shows not only the counties with current monitored air quality above the new standard, but also those counties that are edging up against the new standard. In any of these troublesome counties, it may be difficult, if not impossible, to build new industry because any new emissions, when put into a dispersion model, would predict exceedances of the new annual Pm2.5 NAAQS.

pm 2.5 air quality

Modeled concentrations will vary widely based on emission rate, stack height, terrain, distance to property line, fuel and meteorological conditions. From recent modeling projects I’ve worked on, predicted concentrations have ranged from 0.6 µg/m3 for a new combined cycle turbine and its auxiliary equipment to 3.4 µg/m3 for the contributions from just the nearby sources. It doesn’t take a large source to have an impact of several micrograms per cubic meter. Natural gas, one might think, should have very little Pm2.5 emissions; however Pm2.5 is often the limiting factor when it comes to NAAQS modeling for natural gas facilities. With the new lower annual standard, this will be even truer.

I’m not saying that the new standard isn’t in the best interest for environment and our health nor that the standard isn’t based on the best available science and research. But it is somewhat misleading of EPA to proclaim that these changes will have negligible effects on real companies and real economic growth.

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