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Small Electric Generators
Emissions Regulations
Basic air permitting and emission control requirements are outlined for
each state. The outline used for each state divides the requirements into four categories that are typical for
the structure of air regulations for small generators:
De Minimis Exemptions
State Minor Source Permitting
Major Source Permitting
Emergency Generators
"De Minimis exemption" refers to the fact that most states have a threshold below which units are either
too small or emit a small enough amount that they do not have to apply for a permit of any kind. The requirements
and conditions for these exemptions vary by state, but most states allow some kind of de minimus exemption.
Sources that are not exempted must obtain a permit. An important factor in determining how a source will be
permitted is its Potential to Emit, which is the measure of a source's maximum
possible emissions if operated at full capacity for 8,760 hours per year. If a source's potential emissions exceed
certain emissions thresholds the source is called a Major Source and
is subject to the federal New Source Review permitting process. The New Source
Review trigger threshold depends on the air quality status of the area that the unit is located in. Sources that
fall in between the de minimus and the major thresholds are generally subject to a State Minor Source Permitting.
Both the minor source permit and the major source permit are likely to require some kind of emission limitations
or controls. These control requirements could be anything from raising the stack height of a unit to installing
the most stringent control technologies available. The permitting process also can range from a simple application
to a complex cost-based technology evaluation. The requirements vary depending on the state and the type of unit
proposed. We have tried to include any such requirements under the appropriate section in each state write-up,
however most state regulations have some degree of variabiilty and these summaries cannot capture all possibilities.
Project developers should consult the listed state contacts regarding any specific project.
In addition, most states have special treatment for emergency backup generators. Most states adhere to an EPA
recommendation that states calculate the potential to emit for emergency units based on 500 hours of operation
per year. The treatment of these units has been addressed in a separate category on each page.
*Several states use the term "major source" to refer to a source that triggers
Title V permitting requirements, however in order to prevent confusion this database will only use the term "major
source" when addressing units that trigger the federal New Source Review program.
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