Shades of Gray

Issue 4 and Volume 115.

By Robynn Andracsek, P.E., Burns & McDonnell and Contributing Editor

I used to believe in absolutes: on/off, legal/illegal, pregnant/not pregnant. The Environmental Protection Agency’s greenhouse gas (GHG) Tailoring rule has challenged this viewpoint.

Just as the letter “y” is sometimes a vowel, greenhouse gases are sometimes a PSD pollutant. The short story is that beginning on July 1, GHGs alone can make a source become “major” for Prevention of Significant Deterioration (PSD). The longer story is that sometimes GHGs are a PSD pollutant and sometimes not.

EPA uses a special definition to make GHGs subject to regulation. At a new stationary source, CO2e is a regulated pollutant only if the source will have the potential to emit 100,000 tons per year (tpy) CO2e (and here “e” stands for equivalent). An existing stationary source that has the potential to emit 100,000 tpy CO2e is subject to regulation only when the source makes a physical change that results in an emissions increase of 75,000 tpy CO2e or more. This prevents sources with a potential to emit less than 75,000 tpy CO2e from having CO2e regulated as a pollutant.

Add to this the so-called “anyway” sources. If a project triggers PSD for a pollutant other than CO2e, and CO2e increases by 75,000 tpy, then CO2e trips PSD status since the project is going through PSD “anyway” for the other pollutant. This is true regardless of the existing facility’s CO2e “potential to emit.”

One more confusing element that you need to understand: a difference exists between “mass” and “equivalent” tons. The Clean Air Act requires that pollutants be assessed on a mass basis. But by definition, CO2e is an equivalent measurement, not a strict mass measurement. GHG emissions are not regulated unless the corresponding mass-based trigger, unadjusted for CO2e, also exceeds 100 tpy or 250 tpy (depending on whether or not the source type is listed). For example, 10 tpy sulfur hexafluoride (SF6) equals 326,000 tpy CO2e. But it is less than 100 tpy on a mass basis and would therefore not meet the major PSD source criteria. For combustion processes, the dominant GHG is CO2. Since one ton of CO2 equals one ton CO2e, calculations are simplified.

The only way this all makes sense is to look at some examples.

Plant A has a PTE for each non-GHG pollutant less than 250 tpy, including 50 tpy of PM10. Plant A also has 200,000 tpy CO2e emissions. In October 2011, a project increases the plant’s PM10 by 40 tpy and CO2e by 10,000 tpy. GHGs were not “subject to regulation” before or after the project because there hasn’t been and won’t be a significant increase in CO2e. Therefore, CO2e is not subject to regulation and can’t make the facility a PSD major source. The facility is a minor PSD source both before and after the construction project and PSD won’t apply to the modification.

Plant B has a PTE of 300 tpy NOx and 50,000 tpy CO2e. In November 2011, a project increases the plant’s NOx by 10 tpy and CO2e by 90,000 tpy. GHGs have not become “subject to regulation” prior to the project since the potential to emit of CO2e is less than 100,000 tpy. Therefore, the facility is a major PSD source but CO2e is not a regulated pollutant even though project CO2e PTE is greater than 75,000 tpy. The modification does not trip PSD for CO2e. The source is subject to regulation under PSD for CO2e after the modification.

Plant C has a PTE of 400 tpy NOx and 10,000 tpy CO2e. In October 2011, a project increases the plant’s emissions by 50 tpy NOx and 80,000 tpy CO2e. Since the project trips PSD for NOx (greater than 40 tpy) this project qualifies as an “anyway” source. PSD is triggered for CO2e (since the increase is greater than 75,000 tpy), even though the existing CO2e PTE is less than 100,000 tpy. The same plant has a second project in June 2014. Its current PTE is 90,000 tpy CO2e. The project adds 10 tpy NOx and 80,000 tpy CO2e. Since the NOx increase is less than 40 tpy, NOx does not trip PSD and CO2e does not meet the “anyway” criteria. The PTE for CO2e before the June 2014 project is less than 100,000 tpy, therefore CO2e is not a regulated pollutant and the project does not trip PSD for CO2e. The same quantity of CO2e in the first project is subject to PSD but not in the second project.

Bottom line: Know your facility’s PTE for each pollutant at all times, especially CO2e. It is only then that you can begin to analyze your PSD permitting requirements.

So remember, EPA wrote the Tailoring Rule to establish a “common sense approach to permitting.” Greenhouse gases are now a PSD pollutant…except on alternate Thursdays…unless there is a full moon….

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