(a) Except as provided in § 75.34, the owner or operator shall provide substitute data for each affected unit using a continuous emission monitoring system according to the missing data procedures in this subpart whenever the unit combusts any fuel and:

(1) A valid, quality-assured hour of SO2 concentration data (in ppm) has not been measured and recorded for an affected unit by a certified SO2 pollutant concentration monitor, or by an approved alternative monitoring method under subpart E of this part, except as provided in paragraph (d) of this section; or

(2) A valid, quality-assured hour of flow data (in scfh) has not been measured and recorded for an affected unit from a certified flow monitor, or by an approved alternative monitoring system under subpart E of this part; or

(3) A valid, quality-assured hour of NOX emission rate data (in lb/mmBtu) has not been measured or recorded for an affected unit, either by a certified NOX-diluent continuous emission monitoring system or by an approved alternative monitoring system under subpart E of this part; or

(4) A valid, quality-assured hour of CO2 concentration data (in percent CO2, or percent O2 converted to percent CO2 using the procedures in appendix F to this part) has not been measured and recorded for an affected unit, either by a certified CO2 continuous emission monitoring system or by an approved alternative monitoring method under subpart E of this part; or

(5) A valid, quality-assured hour of NOX concentration data (in ppm) has not been measured or recorded for an affected unit, either by a certified NOX concentration monitoring system used to determine NOX mass emissions, as defined in § 75.71(a)(2), or by an approved alternative monitoring system under subpart E of this part; or

(6) A valid, quality-assured hour of CO2 or O2 concentration data (in percent CO2, or percent O2) used for the determination of heat input has not been measured and recorded for an affected unit, either by a certified CO2 or O2 diluent monitor, or by an approved alternative monitoring method under subpart E of this part; or

(7) A valid, quality-assured hour of moisture data (in percent H2O) has not been measured or recorded for an affected unit, either by a certified moisture monitoring system or an approved alternative monitoring method under subpart E of this part. This requirement does not apply when a default percent moisture value, as provided in §§ 75.11(b) or 75.12(b), is used to account for the hourly moisture content of the stack gas; or

(8) A valid, quality-assured hour of heat input rate data (in mmBtu/hr) has not been measured and recorded for a unit from a certified flow monitor and a certified diluent (CO2 or O2) monitor or by an approved alternative monitoring system under subpart E of this part.

(b) However, the owner or operator shall have no need to provide substitute data according to the missing data procedures in this subpart if the owner or operator uses SO2, CO2, NOX, or O2 concentration, flow rate, percent moisture, or NOX emission rate data recorded from either a certified redundant or regular non-redundant backup CEMS, a like-kind replacement non-redundant backup analyzer, or a backup reference method monitoring system when the certified primary monitor is not operating or is out-of-control. A redundant or non-redundant backup continuous emission monitoring system must have been certified according to the procedures in § 75.20 prior to the missing data period. Non-redundant backup continuous emission monitoring system must pass a linearity check (for pollutant concentration monitors) or a calibration error test (for flow monitors) prior to each period of use of the certified backup monitor for recording and reporting emissions. Use of a certified backup monitoring system or backup reference method monitoring system is optional and at the discretion of the owner or operator.

(c) When the certified primary monitor is not operating or out-of-control, then data recorded for an affected unit from a certified backup continuous emission monitor or backup reference method monitoring system are used, as if such data were from the certified primary monitor, to calculate monitor data availability in § 75.32, and to provide the quality-assured data used in the missing data procedures in §§ 75.31 and 75.33, such as the “hour after” value.

(d) The owner or operator shall comply with the applicable provisions of this paragraph during hours in which a unit with an SO2 continuous emission monitoring system combusts only gaseous fuel.

(1) Whenever a unit with an SO2 CEMS combusts only natural gas or pipeline natural gas (as defined in § 72.2 of this chapter) and the owner or operator is using the procedures in section 7 of appendix F to this part to determine SO2 mass emissions pursuant to § 75.11(e)(1), the owner or operator shall, for purposes of reporting heat input data under § 75.57(b)(5), and for the calculation of SO2 mass emissions using Equation F-23 in section 7 of appendix F to this part, substitute for missing data from a flow monitoring system, CO2 diluent monitor or O2 diluent monitor using the missing data substitution procedures in § 75.36.

(2) Whenever a unit with an SO2 CEMS combusts gaseous fuel and the owner or operator uses the gas sampling and analysis and fuel flow procedures in appendix D to this part to determine SO2 mass emissions pursuant to § 75.11(e)(2), the owner or operator shall substitute for missing total sulfur content, gross calorific value, and fuel flowmeter data using the missing data procedures in appendix D to this part and shall also, for purposes of reporting heat input data under § 75.54(b)(5) or § 75.57(b)(5), as applicable, substitute for missing data from a flow monitoring system, CO2 diluent monitor, or O2 diluent monitor using the missing data substitution procedures in § 75.36.

(3) The owner or operator of a unit with an SO2 monitoring system shall not include hours when the unit combusts only gaseous fuel in the SO2 data availability calculations in § 75.32 or in the calculations of substitute SO2 data using the procedures of either § 75.31 or § 75.33, for hours when SO2 emissions are determined in accordance with § 75.11(e)(1) or (e)(2). For the purpose of the missing data and availability procedures for SO2 pollutant concentration monitors in §§ 75.31 and 75.33 only, all hours during which the unit combusts only gaseous fuel shall be excluded from the definition of “monitor operating hour,” “quality-assured monitor operating hour,” “unit operating hour,” and “unit operating day,” when SO2 emissions are determined in accordance with § 75.11(e)(1) or (e)(2).

(4) During all hours in which a unit with an SO2 continuous emission monitoring system combusts only gaseous fuel and the owner or operator uses the SO2 monitoring system to determine SO2 mass emissions pursuant to § 75.11(e)(3), the owner or operator shall determine the percent monitor data availability for SO2 in accordance with § 75.32 and shall use the standard SO2 missing data procedures of § 75.33.