Inverting the Inversions – Utah and the PM2.5 NAAQS

Posted on February 18, 2014 by James Holtkamp

The valleys and mountains of the Great Basin hold cold air in when a high pressure parks itself overhead, with the result that the valleys with significant populations, primarily the 100+ mile Wasatch Front, are subject to a wintertime PM2.5 grunge that builds up until the next storm front moves in to clear it out.

Although Salt Lake City and other parts of the state are in compliance with the annual PM2.5 NAAQS, exceedances of the 24-hour NAAQS have been recorded during inversion periods since 2006, when EPA lowered that standard from 65 μg/m3 to 35 μg/m3. As a result, Utah is going through an arduous PM2.5 state implementation plan (SIP) revision process to address the PM2.5 nonattainment.

Because we can’t change the topography around here or install fans large enough to blow air out of the valleys, the state must seek reductions in emissions that contribute to the wintertime PM2.5 exceedances. Nearly three-fifths of those emissions are from car and truck emissions. About thirty percent of the contributing emissions are from area sources and wood-burning fireplaces and stoves. And the rest of the emissions –only about a tenth of the PM2.5 precursor and direct emissions – are contributed by large industrial sources in the airshed.

The proposed SIP seeks some reductions from the large industrial sources, which must be retrofit not with RACT but with the equivalent of BACT, notwithstanding hundreds of millions of dollars of pollution control improvements already installed over the last decade. The rest of the PM2.5 emissions to be reduced during inversions must come primarily from mobile source and area emissions.  

The modeling underlying the SIP shows that attainment will barely be reached by the 2019 attainment date. But, with the D.C. Circuit throwing out the PM2.5 implementation rule a year ago and requiring EPA to promulgate a new one under more restrictive provisions of the CAA and the predictable citizen’s suits, who knows if attainment can be achieved short of literally turning out the lights and leaving town.

The Utah Legislature is in session and legislators are falling over each other trying to show that they care about cleaner air. However, there is not much state legislators can do, given that the emissions and fuel standards for mobile sources are set by the federal government (with states having the option of adopting California standards under certain circumstances). So, the state is squeezed between the Wasatch Mountains on the one side and the Clean Air Act on the other. It might be easier to cart off the mountains than to bring the Clean Air Act requirements into alignment with the real world.



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