EPA Redesignates Allegheny Co. as in Attainment for 2012 PM2.5 NAAQS

Several months ago, we blogged about the U.S. Environmental Protection Agency’s proposal to redesignate Allegheny County from nonattainment of the 2012 National Ambient Air Quality Standard (NAAQS) for fine particulate matter to attainment.

We have an update: In the April 16 edition of the Federal Register, EPA published a Final Rule that does, in fact, redesignate Allegheny County to attainment of the 2012 NAAQS for PM_2.5.

To put it another way: It’s official, official now.

Two things to note: 

1. Achieving attainment does not mean that sources of PM_2.5 and regulators can take their feet off the gas, as the regulations that achieved attainment remain on the books as part of what’s known as the Maintenance Plan for Allegheny County.  

2. However, any new major sources of PM_2.5 in Allegheny County, or any new major modifications to existing major sources of PM_2.5, will be subject to Prevention of Significant Deterioration requirements rather than stricter Nonattainment New Source Review requirements. Prevention of Significant Deterioration requirements are designed to ensure that a new source does not knock an area out of attainment of a NAAQS.

April 16’s Final Rule caps a long process that resulted in the closure of several sources of PM_2.5 and the installation of improved emission controls at many others – those are outlined in the November 20, 2025 Proposed Rule for the redesignation.  

“EPA’s redesignation of Allegheny underlines how the Clean Air Act works, albeit slowly, to promote public health,” said GASP Senior Attorney John Baillie.