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New Source Performance Standards (NSPS) are a set of standards defined by the EPA for a variety of emissions sources such as engines, turbines, boilers and many other sources. The rule for compression ignition engines that are powered by diesel fuel is referred to as:

NSPS Subpart IIII: Standards of Performance for Stationary Compression Ignition Internal Combustion Engines (often referred to as “Quad I”, but formally known as 40 CFR Part 60 Subpart IIII).

In the Quad I rule, emission limits for diesel engines are defined in terms of “Tier” levels, that depend upon the maximum power of the engine, the year it was manufactured, and whether it is used for mechanical power or as part of an electrical generator set. Engines that power generator sets are further classified by the EPA as either “Emergency Engines” or “Non-Emergency Engines”, with emission limits that correspond to each application. For example, diesel engines larger than 75 horsepower are currently subject to the “Tier 4 Interim” standard, with “Tier 4 Final” coming in either 2014 or 2015, depending on engine power. Emergency Generator sets are typically “Tier 2”, which has higher emission limits due to the lower number of operating hours, and therefore have less impact on air quality.

Emission Limits and Effective Dates for Diesel Generator Sets:

Emergency Diesel Generator                        Non Emergency Diesel Generator

Please click on above links to see detail.

If you are interested in learning more about how New Source Performance Standards can affect your business, be sure to speak with an AeriNOx Emission expert. We can assist you with any questions you have, including those regarding NSPS Subpart IIII, as well as State and Local emission standards.


More Information on NSPS Subpart IIII

For the most part, compliance with NSPS Quad I is the responsibility of the engine manufacturer, who must ensure the engine meets the emissions standards via a certification process with the EPA. As a result, anyone that purchases an EPA-certified diesel engine is automatically compliant with the Quad I rule.

The certification process has both advantages and disadvantages for customers purchasing diesel engines. On the positive side, they can be assured the engine meets the EPA regulation, which makes the subsequent permitting process with the local air quality authorities much easier. On the other hand, certified engines cost more, as the engine manufacturer both (1) employs state-of-the-art engine and pollution control equipment (known as aftertreatment) to minimize emissions, such as Selective Catalytic Reduction (SCR), Diesel Particulate Filters (DPF) or Diesel Oxidation Catalysts (DOC); and (2) spends considerable time and money testing the engine according to specific EPA test protocols. All of these costs end up being borne by the engine customer. Moreover, the time necessary to certify engines is significant, and even today manufacturers only offer a limited number of models that are compliant with the current Tier 4 Interim standard.

As a result of the higher costs for such “engine + aftertreatment” systems (often as much as 50-70% more than previous models) or because of limited availability of desired engines, some customers consider purchasing an engine then adding lower cost third party aftertreatment separately. While this reduces cost significantly, and can even achieve the same low emission levels as a certified system, the EPA does not allow this practice for NSPS. According to the rule, the customer is compliant with NSPS only when they purchase a diesel engine certified by the manufacturer to meet the EPA standards. (Note: This varies for very large engines, where the certification process is more cumbersome for the manufacturer. Please check with AeriNOx, the Quad I rule directly or your local regulatory authorities for guidance on your specific situation.)

The bottom line is that NSPS Quad I is easy to comply with because the engine manufacturer has already done the hard work of ensuring diesel engine emissions meet the EPA standards. Simply purchase an engine certified to the current EPA Tier standard and you are automatically compliant.