NOx RACT Rule Updates in Illinois – New Annual Compliance Certification (ACC) Report due May 1, 2026

It has been almost one year since the Illinois Pollution Control Board’s final order approving the Illinois Environmental Protection Agency’s (Illinois EPA’s) proposed amendments to Illinois’ air pollution rules for nitrogen oxide (NO_X) emissions, found at Title 35 of the Illinois Administrative Code (35 IAC) Part 217. (These rules are commonly referred to as “NO_X RACT,” where “RACT” is an acronym for “Reasonably Available Control Technology.”) As we first wrote in April 2025, the amendments were implemented to address deficiencies identified by the United States Environmental Protection Agency (USEPA) in the existing rule. At the same time, the Illinois EPA also opted to make the rules more stringent in consideration of the USEPA reclassifying the Greater Chicago Metropolitan and Metro East nonattainment areas (NAAs) as serious NAAs (effective January 16, 2025) for the 2015 ozone National Ambient Air Quality Standard (NAAQS).

Illinois EPA’s updates to 35 IAC Part 217 made the NO_x requirements applicable to more sources, and compliance for all affected sources began on July 1, 2025. There is also a specific reporting requirement for applicable sources to submit an Annual Compliance Certification (ACC) Report, which is due May 1, 2026.

NO_X RACT Applicability

If you have not already done so, we recommend sources which were previously not subject to NO_X RACT review the updated applicability criteria to determine whether they may now be subject.

The most significant change to the applicability criteria was to reduce the source applicability threshold for sources in either NAA from sitewide potential NO_X emissions of 100 tons per year to just 50 tons per year.

1. For example, as of July 1, 2025, the provisions of Subpart Q apply to stationary reciprocating internal combustion engines and turbines located at a source that emits or has the potential to emit NO_x in an amount equal to or greater than 50 tons per year and is in either the area composed of the Chicago area counties of Cook, DuPage, Kane, Lake, McHenry, and Will, the Townships of Aux Sable and Goose Lake in Grundy County, and the Township of Oswego in Kendall County, or in the area composed of the Metro-East counties of Madison, Monroe, and St. Clair, where:
2. A) The engine at nameplate capacity is rated at equal to or greater than 500 bhp output; or
3. B) The turbine is rated at equal to or greater than 3.5 MW (4,694 bhp) output at 14.7 psia, 59°F and 60 percent relative humidity.

The amended rule also retained the “Once In-Always In” general applicability for sources, which provides that any emission unit which was ever subject to NO_X RACT provisions shall remain subject for the entire lifetime of the unit, even if the unit no longer meets the applicability criteria.

NO_X RACT ACC Report Content

Pursuant to 35 IAC 217.156(m), the owner or operator of an emission unit subject to Subpart E, F, G, H, I, or M of 35 IAC Part 217 (industrial boilers; process heaters; glass melting furnaces; cement and lime kilns; iron, steel and aluminum manufacturing; and electrical generating units, respectively) must submit to the Illinois EPA an ACC report that demonstrates compliance with the applicable requirements for the preceding calendar year by May 1 of the following year. 35 IAC 217.396(d) requires the same for the owner or operator of an emission unit subject to Subpart Q (stationary reciprocating internal combustion engines and turbines). Both ACC reports must include the following:

1. Identification, type (e.g., gas-fired), and location of the applicable emission unit.
2. Methods used for determining compliance, including an emissions averaging plan, if applicable, a description of test methods, monitoring, recordkeeping, and reporting requirements.
3. A certification of compliance with the applicable emissions limitation or identification of the periods of noncompliance with a quantification of the excess emissions limitation and the excess emissions.
4. For each calendar month, the highest 30-day rolling average emission rate. The emissions data must be reported in the measurement units of the applicable emissions limitation.
5. The emission unit’s daily and total operating hours, capacity utilization, and the percent operation of any Continuous Emission Monitoring System (CEMS) or Predictive Emission Monitoring System (PEMS) during the hours the emission unit was operating.
6. A certification of compliance with all applicable requirements except those identified signed by a responsible official that contains the following: “I certify, based on information and belief formed after reasonable inquiry, the statements and information in the document are true, accurate, and complete.”

Furthermore, if demonstrating compliance through an emissions averaging plan (see #2 above), an additional report (also required by May 1) is required and must include the following information [35 IAC 217.156(j)/35 IAC 217.396(c)(5)]:

7. For all units that are part of the emissions averaging plan, the total mass of allowable NO_X emissions on a 30-day rolling average basis.
8. The total mass of actual NO_X emissions on a 30-day rolling average basis for each unit included in the averaging plan.
9. The calculations that demonstrate that the total mass of actual NO_X emissions is less than the total mass of allowable NO_X emissions using the appropriate equations in 35 IAC Part 217.
10. The daily information required to determine the total mass of actual NO_X emissions on a 30-day rolling average basis.

NO_X RACT ACC Report Submittal

1. The ACC may be submitted to the Illinois EPA along with the Annual Emissions Report required by 35 IAC 254 or along with the compliance certification required under Illinois General Assembly – 415 ILCS 5/39.5(7)(p)(v) Environmental Protection Act. For Title V Clean Air Act Permit Program (CAAPP) Permit facilities, Trinity recommends submitting the NOx RACT ACC as part of the facility’s compliance certification.
2. The due date for the NOx RACT ACC is May 1, 2026. This is certifying compliance for the time period of July 1, 2025 through December 31, 2025. For the ACC due May 1, 2027, the compliance certification time-period will be from January 1, 2026 through December 31, 2026.

Be sure to include the information in the section titled NOx RACT ACC Report Content above in your ACC submittal to Illinois EPA due May 1, 2026 and in your subsequent ACCs, for any applicable emission units (per 35 IAC Part 217).

For further assistance regarding this report or the general updates to NO_X RACT, please do not hesitate to contact Rebecca Collins or Connor Rutledge of Trinity’s Chicago area office, or consider calling the main office line at 630.495.1470.