Input Requested on PSD Increment Consumption
Posted: 08/31/2011
The EPA is requesting clarification from states in how designations should be specified for the new 1-hour NO2 national ambient air quality standard (NAAQS). While EPA currently has no plans to do so, should EPA promulgate a 1-hour NO2 increment, the designations approach used does have possible implications to prevention of significant deterioration (PSD) permitting. The Department is requesting feedback on a preferred approach to the 1-hour NO2 NAAQS designations. The available options include either a statewide or county-by-county designation. The options and possible implications of each approach are discussed below. If you have a preference please provide your recommendation to Matthew Johnson at or at (515) 242-5164 by Tuesday, September 6.

In Iowa, where all areas are expected to be designated by EPA as unclassifiable relative to the 1-hour NO2 national ambient air quality standard (NAAQS), designations could be specified in one of two ways. EPA could designate the entire state as unclassifiable. Alternatively, each county could be designated individually as unclassifiable. While these options appear identical in that all areas in the state receive the same designation, these two approaches create differences in how PSD increment consumption analyses would be conducted if EPA were to promulgate 1-hour NO2 increments.
The PSD program was enacted to prevent air quality in attainment areas from deteriorating past certain limits. The limits are referred to increments, which place restrictions on how much air quality can degrade in an area.  The specific procedures used in an increment analysis relate to how designations are specified (in 40 CFR 81) and the resultant impacts upon how the minor source baseline date is determined. The minor source baseline date defines when growth in minor source emissions starts to consume the available increment in an area.
The state is currently designated as a single, state-wide area for the annual NO2 NAAQS. In this situation, should a facility need to complete a NO2 PSD increment analysis, this state-wide or ‘entire-state’ designation method yields a single minor source baseline date used in all PSD increment analysis for any area in the state. In other words, all locations in the state share a known and consistent minor source baseline date, making tracking of increment consumption much simpler. If the state were to be designated on a county-by-county basis the minor source baseline date would not be triggered statewide, but would instead be triggered on a county-by-county basis. Compared to the statewide designation approach this creates two notable differences in the PSD increment analysis process. First, different areas in the state will have unique minor source baseline dates, each established by the first complete PSD application received for that area. This may comparatively increase the amount of increment available, as having a more recent minor source baseline date reduces the amount time over which growth in minor source emissions would be considered in the increment analysis.
Second, since there is no single statewide minor source baseline date it is possible for a PSD project to locate near several areas, each having their own minor source baseline dates. This option increases the complexity of the emissions tracking efforts.  The PSD applicant would need to account for minor source emissions growth according to a different minor source baseline date for each area. The difficulties introduced by the additional emissions tracking and accounting requirements could outweigh the benefits gained in increased increment availability.
In summary, the entire-state designations approach provides simplicity in that a single fixed date applicable statewide for all PSD applications is established for tracking the impacts upon increment from minor source growth. Alternatively the county-by-county approach provides greater flexibility in terms of when minor sources start consuming increment, but places a greater burden upon the PSD applicant for possible multi-year emissions tracking and accounting requirements.