(a) Definitions. All terms not defined in this paragraph (a) shall have the meaning given to them in the Act and in subpart A of 40 CFR part 60.

Affected unit means an industrial boiler meeting the applicability criteria of this section.

Boiler means an enclosed device using controlled flame combustion and having the primary purpose of recovering thermal energy in the form of steam or hot water. Controlled flame combustion refers to a steady-state, or near steady-state, process wherein fuel and/or oxidizer feed rates are controlled.

Coal means “coal” as defined in 40 CFR 60.41b.

Distillate oil means “distillate oil” as defined in 40 CFR 60.41b.

Maximum heat input capacity means means the ability of a steam generating unit to combust a stated maximum amount of fuel on a steady state basis, as determined by the physical design and characteristics of the steam generating unit.

Natural gas means “natural gas” as defined in 40 CFR 60.41.

Operating day means a 24-hour period between 12:00 midnight and the following midnight during which any fuel is combusted at any time in the steam generating unit. It is not necessary for fuel to be combusted continuously for the entire 24-hour period.

Residual oil means “residual oil” as defined in 40 CFR 60.41c.

(b) Applicability. (1) The requirements of this section apply to each new or existing boiler with a design capacity of 100 mmBtu/hr or greater that receives 90% or more of its heat input from coal, residual oil, distillate oil, natural gas, or combinations of these fuels in the previous ozone season, is located at sources that are within the Basic Chemical Manufacturing industry, the Petroleum and Coal Products Manufacturing industry, the Pulp, Paper, and Paperboard industry, the Metal Ore Mining industry, and the Iron and Steel and Ferroalloys Manufacturing industry and which is located within any of the States listed in § 52.40(c)(2), including Indian country located within the borders of any such State(s). The requirements of this section do not apply to an emissions unit that meets the requirements for a low-use exemption as provided in paragraph (b)(2) of this section.

(2) If you are the owner or operator of a boiler meeting the applicability criteria of paragraph (b)(1) of this section that operates less than 10% per year on an hourly basis, based on the three most recent years of use and no more than 20% in any one of the three years, you are exempt from meeting the emissions limits of this section and are only subject to the recordkeeping and reporting requirements of paragraph (f)(2) of this section.

(i) If you are the owner or operator of an affected unit that exceeds the 10% per year hour of operation over three years or the 20% hours of operation per year criteria, you can no longer comply via the low-use exemption provisions and must meet the applicable emissions limits and other applicable provisions as soon as possible but not later than one year from the date eligibility as a low-use boiler was negated by exceedance of the low-use boiler criteria.

(ii) [Reserved]

(c) Emissions limitations. If you are the owner or operator of an affected unit, you must meet the following emissions limitations on a 30-day rolling average basis during the 2026 ozone season and in each ozone season thereafter:

(1) Coal-fired industrial boilers: 0.20 lbs NOX/mmBtu;

(2) Residual oil-fired industrial boilers: 0.20 lbs NOX/mmBtu;

(3) Distillate oil-fired industrial boilers: 0.12 lbs NOX/mmBtu;

(4) Natural gas-fired industrial boilers: 0.08 lbs NOX/mmBtu; and

(5) Boilers using combinations of fuels listed in paragraphs (c)(1) through (4) of this section: such units shall comply with a NOX emissions limit derived by summing the products of each fuel's heat input and respective emissions limit and dividing by the sum of the heat input contributed by each fuel.

(d) Testing and monitoring requirements. (1) If you are the owner or operator of an affected unit, you shall conduct an initial compliance test as described in 40 CFR 60.8 using the continuous system for monitoring NOX specified by EPA Test Method 7E of 40 CFR part 60, appendix A-4, to determine compliance with the emissions limits for NOX identified in paragraph (c) of this section. In lieu of the timing of the compliance test described in 40 CFR 60.8(a), you shall conduct the test within 90 days from the installation of the pollution control equipment used to comply with the NOX emissions limits in paragraph (c) of this section and no later than May 1, 2026.

(i) For the initial compliance test, you shall monitor NOX emissions from the affected unit for 30 successive operating days and the 30-day average emissions rate will be used to determine compliance with the NOX emissions limits in paragraph (c) of this section. You shall calculate the 30-day average emission rate as the average of all hourly emissions data recorded by the monitoring system during the 30-day test period.

(ii) You are not required to conduct an initial compliance test if the affected unit is subject to a pre-existing, federally enforceable requirement to monitor its NOX emissions using a CEMS in accordance with 40 CFR 60.13 or 40 CFR part 75.

(2) If you are the owner or operator of an affected unit with a heat input capacity of 250 mmBTU/hr or greater, you are subject to the following monitoring requirements:

(i) You shall install, calibrate, maintain, and operate a continuous emissions monitoring system (CEMS) for measuring NOX emissions and either oxygen (O2) or carbon dioxide (CO2), unless the Administrator has approved a request from you to use an alternative monitoring technique under paragraph (d)(2)(vii) of this section. If you have previously installed a NOX emissions rate CEMS to meet the requirements of 40 CFR 60.13 or 40 CFR part 75 and continue to meet the ongoing requirements of 40 CFR 60.13 or 40 CFR part 75, that CEMS may be used to meet the monitoring requirements of this section.

(ii) You shall operate the CEMS and record data during all periods of operation during the ozone season of the affected unit except for CEMS breakdowns and repairs. You shall record data during calibration checks and zero and span adjustments.

(iii) You shall express the 1-hour average NOX emissions rates measured by the CEMS in terms of lbs/mmBtu heat input and shall be used to calculate the average emissions rates under paragraph (c) of this section.

(iv) Following the date on which the initial compliance test is completed, you shall determine compliance with the applicable NOX emissions limit in paragraph (c) of this section during the ozone season on a continuous basis using a 30-day rolling average emissions rate unless you monitor emissions by means of an alternative monitoring procedure approved pursuant to paragraph (d)(2)(vii) of this section. You shall calculate a new 30-day rolling average emissions rate for each operating day as the average of all the hourly NOX emissions data for the preceding 30 operating days.

(v) You shall follow the procedures under 40 CFR 60.13 for installation, evaluation, and operation of the continuous monitoring systems. Additionally, you shall use a span value of 1000 ppm NOX for affected units combusting coal and span value of 500 ppm NOX for units combusting oil or gas. As an alternative to meeting these span values, you may elect to use the NOX span values determined according to section 2.1.2 in appendix A to 40 CFR part 75.

(vi) When you are unable to obtain NOX emissions data because of CEMS breakdowns, repairs, calibration checks and zero and span adjustments, you will obtain emissions data by using standby monitoring systems, Method 7 of 40 CFR part 60, appendix A-4, Method 7A of 40 CFR part 60, appendix A-4, or other approved reference methods to provide emissions data for a minimum of 75 percent of the operating hours in each affected unit operating day, in at least 22 out of 30 successive operating days.

(vii) You may delay installing a CEMS for NOX until after the initial performance test has been conducted. If you demonstrate during the performance test that emissions of NOX are less than 70 percent of the applicable emissions limit in paragraph (c) of this section, you are not required to install a CEMS for measuring NOX. If you demonstrate your affected unit emits less than 70 percent of the applicable emissions limit chooses to not install a CEMS, you must submit a written request to the Administrator that documents the results of the initial performance test and includes an alternative monitoring procedure that will be used to track compliance with the applicable NOX emissions limit(s) in paragraph (c) of this section. The Administrator may consider the request and, following public notice and comment, may approve the alternative monitoring procedure with or without revision, or disapprove the request. Upon receipt of a disapproved request, you will have one year to install a CEMS.

(3) If you are the owner or operator of an affected unit with a heat input capacity less than 250 mmBTU/hr, you must monitor NOX emission via the requirements of paragraph (e)(1) of this section or you must monitor NOX emissions by conducting an annual test in conjunction with the implementation of a monitoring plan meeting the following requirements:

(i) You must conduct an initial performance test over a minimum of 24 consecutive steam generating unit operating hours at maximum heat input capacity to demonstrate compliance with the NOX emission standards under paragraph (c) of this section using Method 7, 7A, or 7E of appendix A-4 to 40 CFR part 60, Method 320 of appendix A to 40 CFR part 63, or other approved reference methods.

(ii) You must conduct annual performance tests once per calendar year to demonstrate compliance with the NOX emission standards under paragraph (c) of this section over a minimum of 3 consecutive steam generating unit operating hours at maximum heat input capacity using Method 7, 7A, or 7E of appendix A-4 to 40 CFR part 60, Method 320 of appendix A to 40 CFR part 63, or other approved reference methods. The annual performance test must be conducted before the affected units operates more than 400 hours in a given year.

(iii) You must develop and comply with a monitoring plan that relates the operational parameters to emissions of the affected unit. The owner or operator of each affected unit shall develop a monitoring plan that identifies the operating conditions of the affected unit to be monitored and the records to be maintained in order to reliably predict NOX emissions and determine compliance with the applicable emissions limits of this section on a continuous basis. You shall include the following information in the plan:

(A) You shall identify the specific operating parameters to be monitored and the relationship between these operating parameters and the applicable NOX emission rates. Operating parameters of the affected unit include, but are not limited to, the degree of staged combustion (i.e., the ratio of primary air to secondary and/or tertiary air) and the level of excess air (i.e., flue gas O2 level).

(B) You shall include the data and information used to identify the relationship between NOX emission rates and these operating conditions.

(C) You shall identify: how these operating parameters, including steam generating unit load, will be monitored on an hourly basis during periods of operation of the affected unit; the quality assurance procedures or practices that will be employed to ensure that the data generated by monitoring these operating parameters will be representative and accurate; and the type and format of the records of these operating parameters, including steam generating unit load, that you will maintain.

(4) You shall submit the monitoring plan to the EPA via the CEDRI reporting system, and request that the relevant permitting agency incorporate the monitoring plan into the facility's title V permit.

(e) Recordkeeping requirements. (1) If you are the owner or operator of an affected unit, which is not a low-use boiler, you shall maintain records of the following information for each day the affected unit operates during the ozone season:

(i) Calendar date;

(ii) The average hourly NOX emissions rates (expressed as lbs NO2/mmBtu heat input) measured or predicted;

(iii) The 30-day average NOX emissions rates calculated at the end of each affected unit operating day from the measured or predicted hourly NOX emissions rates for the preceding 30 steam generating unit operating days;

(iv) Identification of the affected unit operating days when the calculated 30-day rolling average NOX emissions rates are in excess of the applicable NOX emissions limit in paragraph (c) of this section with the reasons for such excess emissions as well as a description of corrective actions taken;

(v) Identification of the affected unit operating days for which pollutant data have not been obtained, including reasons for not obtaining sufficient data and a description of corrective actions taken;

(vi) Identification of the times when emissions data have been excluded from the calculation of average emissions rates and the reasons for excluding data;

(vii) Identification of “F” factor used for calculations, method of determination, and type of fuel combusted;

(viii) Identification of the times when the pollutant concentration exceeded full span of the CEMS;

(ix) Description of any modifications to the CEMS that could affect the ability of the CEMS to comply with Performance Specification 2 or 3 in appendix B to 40 CFR part 60;

(x) Results of daily CEMS drift tests and quarterly accuracy assessments as required under Procedure 1 of 40 CFR part 60, appendix F; and

(xi) The type and amounts of each fuel combusted.

(2) If you are the owner or operator of an affected unit complying as a low-use boiler, you must maintain the following records consistent with the requirements of § 52.40(g):

(i) Identification and location of the boiler;

(ii) Nameplate capacity;

(iii) The fuel or fuels used by the boiler;

(iv) For each operating day, the type and amount of fuel combusted, and the date and total number of hours of operation; and

(v) the annual hours of operation for each of the prior 3 years, and the 3-year average hours or operation.

(f) Reporting requirements. (1) If you are the owner or operator of an affected unit, you must submit the results of the performance test or performance evaluation of the CEMS following the procedures specified in § 52.40(g) within 60 days after the date of completing each performance test required by this section.

(2) If you are the owner or operator of an affected unit, you are required to submit excess emissions reports for any excess emissions that occurred during the reporting period. Excess emissions are defined as any calculated 30-day rolling average NOX emissions rate, as determined under paragraph (e)(1)(iii) of this section, that exceeds the applicable emissions limit in paragraph (c) of this section. Excess emissions reports must be submitted in PDF format to the EPA via CEDRI or analogous electronic reporting approach provided by the EPA to report data required by this section following the procedures specified in § 52.40(g).

(3) If you are the owner or operator an affected unit subject to the continuous monitoring requirements for NOX under paragraph (d) of this section, you shall submit reports containing the information recorded under paragraph (d) of this section as described in paragraph (e)(1) of this section. You shall submit compliance reports for continuous monitoring in PDF format to the EPA via CEDRI or analogous electronic reporting approach provided by the EPA to report data required by this section following the procedures specified in § 52.40(g).

(4) If you are the owner or operator of an affected unit, you shall submit an annual report in PDF format to the EPA by January 30th of each year via CEDRI or analogous electronic reporting approach provided by the EPA to report data required by this section. Annual reports shall be submitted following the procedures in § 52.40(g).