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NESHAP are a set of standards defined by the EPA for a variety of hazardous air pollutants known as HAPs.  Some of these include formaldehyde, acrolein and acetaldehyde.  But there are many more HAPs defined by the EPA –189 to be precise, although not all are found in engine exhaust.  (For the complete list of HAPs, see

There are many NESHAP regulations for emissions sources such as engines, turbines, boilers and many other sources. The rule for compression ignition and spark-ignited engines is referred to as:

NESHAP Subpart ZZZZ:  National Emission Standards for Hazardous Air Pollutants for Stationary Reciprocating Internal Combustion Engines:  (often referred to as the RICE NESHAP Rule or simply “Quad Z”, but the rule is formally known as 40 CFR Part 63 Subpart ZZZZ).

On January 30 2013, the EPA issued a revision to Quad Z that addresses several concerns voiced by stakeholders regarding the technical and commercial challenges in meeting the rule as it was adopted in 2010.  The revisions finalized in the most recent rule provide greater flexibility to owners and operators of diesel and natural gas engines, as well as expands the use of emergency engines for non-emergency use.  [Note:  The EPA has subsequently been approached by several organizations requesting that the EPA “reconsider” many of the final revisions, suggesting the RICE NESHAP is still subject to change at some point in the future.]

An important point to consider is that even with the very recent changes currently on record, the newly revised rule maintains the required compliance dates as in previous versions:

  • Compression Ignition EnginesMay 3, 2013
  • Spark-Ignited EnginesOctober 19, 2013


An important difference of NESHAP is that compliance is the responsibility of the engine owner or operator.

If you are interested in learning more about how RICE NESHAP 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 NESHAP Subpart ZZZZ, as well as State and Local emission standards.

The compliance requirements are specified for about 80 different engine classifications, based on fuel type (i.e., diesel  or natural gas), engine horsepower, date the engine was ordered, application (e.g., emergency or non-emergency use), and with the recent revision, where the engine is actually operated.  Another critical parameter in understanding compliance requirements is whether the engine is located in a “Major Source” of HAP emissions or an “Area Source” of HAP emissions.  A Major Source refers to a source that emits either 10 tons per year of any one HAP (e.g., formaldehyde), or 25 tons per year of any combination of HAPs (e.g., formaldehyde + acrolein).  An Area Source is everything that isn’t defined as a major source.  A “source” can be a single engine or group of engines at a site or facility.

While the actual requirements are too numerous to discuss here, they generally fall into two categories:  (1) management practices such as proper engine maintenance, or (2) installing an catalyst to reduce emissions of CO or formaldehyde.  Other requirements include recordkeeping and reporting engine operation and maintenance schedules to the EPA or local regulatory authority. The requirements are very different for each classification, so check with your permit authorities if you are unsure which designation you fall under.