Mass Confusion: Are Greenhouse Gases for PSD Permitting Treated the Same Way as Other Regulated PSD Pollutants?

Can a facility be a classified as a major stationary source for greenhouse gas (GHG) emissions only, and if so, do all modifications at the facility need to be evaluated for Prevention of Significant Deterioration (PSD) applicability for all New Source Review (NSR) regulated pollutants?  Since we are now well into implementation of the GHG Tailoring Rule, one would expect that there should be a simple answer for such basic questions – right?  ALL4’s John Slade set out to provide a “plain English” explanation but, as is typical with anything related to NSR applicability, nothing is simple.  Undaunted, John provides his explanation below.

But before getting into these questions that surely perplex you, it is important to review some of the new and unique terms we must use when discussing this topic.

•  Tailoring Rule refers to the Prevention of Significant Deterioration (PSD) and Title V Greenhouse Gas (GHG) Tailoring Rule published at 75 FR 31514 (June 3, 2010), which sets the timing and thresholds for addressing GHG emissions from stationary sources under the Clean Air Act (CAA) permitting programs.

• GHG means the sum of the following six well-mixed gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (NO2), sulfur hexafluoride (SF6), hydrofluorocarbons (HFC), and perfluorocarbons (PFCs).  For PSD applicability purposes, GHG is calculated in two (2) different ways (i.e., on a mass basis and expressed as a carbon dioxide equivalent (CO2e)).
• GHG on a mass basis is calculated by summing the mass amount of emissions of the six well-mixed gases.
• GHG expressed as CO2e is calculated by summing the resultant values from multiplying the mass amount of each of the six well-mixed gases by each gas’s associated global warming potential.
• Global warming potential (GWP) is a measure of how much a given mass of each gas is estimated to contribute to global warming.  It is a relative scale which compares the gas in question to CO2.
• Potential to emit (PTE) means maximum potential to emit a pollutant.
• “Subject to regulation” means that below a certain threshold, a pollutant is simply not regulated and you can forget about it (sort of).  For all NSR regulated pollutants other than GHGs, that level is zero.  For GHGs, a stationary source is not subject to regulation unless the GHGs equal or exceed 100,000 tpy CO2e.  For a modification, GHGs are not subject to regulation unless the emissions increase equals or exceeds 75,000 tpy CO2e.
• An “anyway source” is a stationary source that is major for a non-GHG pollutant (e.g., it is major for one or more criteria pollutants).
• A “GHG-only source” is a stationary source whose CO2e emissions are greater than 100,000 tpy and GHG mass emissions are greater than 100/250 tpy on a mass basis.   All other NSR regulated pollutants have a PTE less than the major stationary source thresholds.

Prior to the Tailoring Rule, the first question you would ask in a PSD applicability determination is whether or not the source was major for any PSD regulated pollutant.  Now (post-Tailoring Rule) you have to ask two questions:  (1) what pollutants emitted by the facility are subject to regulation; and (2)

Prior to the Tailoring Rule, the first question you would ask in a PSD applicability determination is whether or not the source was major for any NSR regulated pollutant.  Now (post-Tailoring Rule) you have to ask two questions:  (1) what pollutants emitted by the facility are subject to regulation; and (2) is the source a major source for any NSR pollutants subject to regulation.  For the non-GHG pollutants it’s easy, since any emissions over zero are subject to regulation.  For GHGs, it’s not so simple.  Emissions from the source must be greater than 100,000 tpy CO2e to be subject to regulation (first question) and greater than 100/250 tpy on a mass basis (second question) in order to be a major source for GHGs.  For modifications, the two questions are similar:  (1) will the project result in emissions increases from any pollutants subject to regulation; and (2) will the emissions increases of pollutants subject to regulation equal or exceed the significant emission rates (SERs).  For non-GHG pollutants any increase in emissions is subject to regulation and we are all familiar with the SERs in 40 CFR §52.21.  For GHGs, an emissions increase is not subject to regulation unless the increase in emissions equals or exceeds 75,000 CO2e and the mass emissions increase is greater than zero.

A confusing situation regarding the applicability of PSD occurs when a facility makes a modification at a GHG-only source.  The confusion relates to the applicability (or non-applicability) of PSD to non-GHG regulated NSR pollutants.  As you know (or used to know), a source only has to be a major stationary source for one PSD pollutant in order to trigger the requirement to review a modification for all PSD pollutants at their SERs.  However, for a GHG-only source, the emissions increase is subject to regulation only if the emissions increase results in an increase of GHGs greater than or equal to 75,000 CO2e.  So at a GHG-only source, a modification can result in emissions increases of, for instance, criteria pollutants above their SERs, and not trigger PSD if the increase in GHGs is less than 75,000 tpy CO2e.

Let’s try some examples:

Each scenario and the associated air permitting implications are discussed below.