Subpart IIII

In a previous blog entry regarding the ZZZZ and JJJJ RICE Rules , we discussed the National Emissions Standards for Hazardous Air Pollutants for Reciprocating Internal Combustions Engines (RICE NESHAP), and the New Source Performance Standards (NSPS) for Spark Ignition RICE Units, more commonly referred to as Subparts ZZZZ and JJJJ, respectively. There is another related rule that bears consideration, and that is Subpart IIII, the NSPS for Compression Ignition Internal Combustion Units (CI ICE).

There are two basic types of Stationary Reciprocating engines: spark ignition and compression ignition. Spark ignition engines use a spark, across a spark plug, to ignite a compressed fuel-air mixture. Typically, fuels for these engines are gasoline and natural gas. Compression ignition engines compress air to a high pressure, heating the air to the ignition temperature of the fuel, which is then injected. The high compression ratio used for compression ignition engines results in a higher efficiency than is possible with spark ignition engines. Diesel fuel oil is normally used in compression ignition engines, although there are dual-fueled varieties, where natural gas is compressed with the combustion air, and diesel oil is injected at the top of the compression stroke to initiate combustion.

The requirements of the Subpart IIII standards, particularly as they are related to performance testing, are dependent on the size of the engine, the manufacture date, the cylinder displacement, and whether it is used for emergency or non-emergency purposes. The EPA defines an emergency engine as one that is used for the purpose of maintenance checks and readiness testing, and is operated less than 100 hours per year. The owner of the emergency engine can NOT connect the engine to the grid under financial incentive and maintain the unit status as an emergency engine. Therefore, a peak shaving engine will not be classified as an emergency unit under the definitions of the Subparts.

For engines that are required to comply with Subpart IIII, including those engines located at Area Sources and engines less than or equal to 500hp located at Major Sources, there are no further requirements under the RICE NESHAP (Subpart ZZZZ). A Major Source is one that has the potential to emit 10 tons per year of any individual Hazardous Air Pollutant (HAP), or 25 tons per year of all HAPs. An Area Source is any source that is not considered a Major Source under this definition.

Regarding stack testing, an owner or operator of a CI ICE non-emergency unit built after 2007 with a displacement of >30L must demonstrate compliance by a performance test (stack test) for emissions of Particulate Matter (PM) and Oxides of Nitrogen (NOx). There are two methods for demonstrating compliance with either pollutant. The first is to show a percent reduction in emissions, and requires sampling for that pollutant at both the inlet and outlet to the control device for the source. Per IIII requirements, NOx must be reduced by 90% and PM by 60%. The second option is to limit the mass emission rate in the exhaust and only requires sampling at the outlet of the unit. The emission limit for NOx is 1.6 g/KW-hr (1.2 g/HP-hr). The emission limit for PM is 0.15g/KW-hr (0.11 g/HP-hr). In addition to the initial compliance performance test, owners of such engines must then perform annual performance tests to prove continued compliance with the standards.

The NESHAP and NSPS rulings can be an impenetrable maze without expert assistance, and the performance testing requirements can have a substantial impact on a facility’s operating budget. It is important to have a partner that is reliable and knowledgeable when approaching the many new emissions requirements being promulgated by the EPA and state governments. For assistance with your compliance needs, and performance testing requirements, ESS is available to help. If you believe you will or may have compliance issues under Subpart IIII, ZZZZ, or JJJJ, give us a call or an email today: 910-799-1055

Brian Mellor About Brian Mellor

Brian Mellor works with Environmental Source Samplers, Inc. (ESS), an environmental consulting firm specializing in stack testing, CEMS Testing, and EPA air emissions compliance.

ESS has conducted international stack testing projects at Johnson Atoll, in the Philippines, the Dominican Republic, Hong Kong, and various parts of Europe. If you need a team that will do your international job with efficiency and effectiveness, call ESS at (910) 799-1055 or visit

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