An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Clean Air Markets

New and Revised Questions and Answers

The following part 75 monitoring Q&As are either new or revised and have not yet been added to the Part 75 Emissions Monitoring Policy Manual PDF document.

Section 7: Backup and Portable Monitoring - Question 7.14

Topic: Testing requirements for like-kind analyzers used more than 720 hours

Question: What tests are required to use a like-kind analyzer for more than 720 hours per calendar year?

Answer: If a like-kind analyzer is used for more than 720 hours per calendar year at a monitoring location, you must update the monitoring plan to add the analyzer as a component of a regular non-redundant backup system. In addition, the monitoring system, including the like-kind analyzer must pass a relative accuracy test audit (RATA) at that monitoring location prior to reporting data greater than 720 hours per calendar year at a monitoring location or you must report the data as invalid.

In the case where a like-kind analyzer replaces one component of a NOx-diluent monitoring system, a RATA is required on the complete NOx-diluent monitoring system, not just the like-kind analyzer component. For example, if you replace a CO2 analyzer in a NOx-diluent monitoring system with a like-kind analyzer and the NOx concentration monitor continues to function normally, you must still conduct a relative accuracy test audit (RATA) on the NOx-diluent monitoring system in lb/mmBtu.

If a like-kind analyzer is used for more than 720 hours in a calendar year, but not more than 720 hours at a single monitoring location during the calendar year (i.e., the like-kind analyzer was used at two or more monitoring locations for less than 720 hours in each location), a RATA is not required.

References: § 75.20(d)(2)(v)

History: Added on September 28, 2020

Top of Page

Section 8: Relative Accuracy - Question 8.15

Topic: RATA load requirements for common stacks

Question: Our company has a plant with three units using a common stack. One of those units experienced an unscheduled outage during the last quarter in which we should perform an annual flow RATA at three load levels. Should we wait to perform the RATA for flow until all three units are operating again?

Answer: Every effort should be made to perform the relative accuracy test audit by the end of the required quarter. Section of appendix A defines the range of operation for a unit or common stack. For common stacks, the range of operation extends from the minimum safe, stable load of any unit using the stack to the highest sustainable load with all units in operation. Section further defines the low, mid, and high load levels as 0–30%, 30–60%, and 60–100% of the range of operation, respectively.

Therefore, in the present example, if a load level of at least 60% of the range of operation could be attained with two units in operation, this would suffice for the high-level flow RATA. The mid- and low-flow tests could then be done at 35% and 10% of the operating range, respectively (note that section 6.5.2 of appendix A requires a minimum separation of 25% of the operating range between adjacent load levels).

If, however, a true high level data point is not attainable with only two units in operation, then if it is expected that all three units will be back in service soon after the end of the quarter, perform the high-level flow RATA within the 720 unit operating hour grace period allowed under section 2.3.3 of appendix B. If it is expected that all three units will not be back in service within the 720 unit-operating-hour grace period, contact your EPA monitoring analyst.

References: appendix A, sections 6.5.2 and; appendix B, sections 2.3.1 and 2.3.3

History: First published in March 1995, Update #5; revised in October 1999 Revised Manual; revised in 2013 Manual, Revised 9/25/2019]

Top of Page

Section 13: DAHS, Recordkeeping, and Reporting - Question 13.18

Topic: Minimum data acquisition and handling system requirements for units reporting using the low-mass emitter (LME) methodology

Question: What are the minimum requirements for a data acquisition and handling system (DAHS) for low-mass emitter (LME) units?

Answer: For LME units, a DAHS is not required. Quality assurance test information, monitoring plans, fuel sampling results, and quarterly emissions data for LME units may be generated using the LME module of the ECMPS client tool or imported into ECMPS in XML format.

References: appendix A, section 4

History: First published in November 1995, Update #7; revised in 2013 Manual, revised on 4/24/2019 to reflect DAHS requirements for LME

Top of Page

Section 23: Appendix D - Question 23.21

Topic: Establishment of the fuel flow-to-load ratio test baseline

Question: May I use an initial fuel flow meter certification per appendix D, section to establish the beginning of a baseline fuel flow-to-load ratio?

Answer: Yes, baseline data collection may begin with the first hour of fuel flowmeter operation following completion of the most recent quality assurance procedure, including initial fuel flow meter certification.

References: appendix D, sections 2.1.7

History: Added on September 28, 2020

Top of Page

Section 23: Appendix D - Question 23.22

Topic: Fuel flowmeter minimum data capture requirements

Question: What are the hourly minimum data capture requirements for fuel flowmeters?

Answer: Each fuel flowmeter must meet the minimum data capture requirement for continuous monitoring systems in § 75.10(d)(1)—a minimum of one valid data point (e.g., one-minute average) must be obtained in each 15-minute quadrant of each unit operating hour, except when required quality assurance activities are conducted during the hour, in which case, only two valid data points, separated by at least 15-minutes, are required.

References: § 75.10(d)(1)

History: Added on September 28, 2020

Top of Page

Section 23: Appendix D - Question 23.23

Topic: Multi-hole orifice plates

Question: For multi-hole orifice plates, can I use American Gas Association (AGA) Report No. 3 or ASME MFC-3M as an acceptable method for meeting the initial fuel flow meter certification requirements found in section 2.1.5 of appendix D or the ongoing fuel flow meter quality assurance requirements found in section 2.1.6 of appendix D?

Answer: No, the design specifications in AGA Report No. 3 and ASME MFC-3M that are used to meet the requirements of part 75 are for single-hole orifice plates, defined in the reports as a single circular concentric aperture. A multi-hole orifice plate does not meet the initial certification requirements of section 2.1.5 of appendix D by design. However, a multi-hole orifice plate can meet the initial certification and ongoing quality assurance requirements of sections 2.1.5 and 2.1.6, respectively, by conforming with the testing requirements detailed in section of appendix D.

References: appendix D, sections 2.1.5 and 2.1.6

History: Added on September 28, 2020

Top of Page

Section 27: Low Mass Emitters - Question 27.22

Topic: Startups, shutdowns, and partially controlled hours in the low-mass emitter (LME) methodology

Question: For units with add-on NOx controls, dry low-NOx burners, or steam or water injection, what should be reported for hours when the monitored parameters are not within the acceptable envelopes for either the full hour or partial hour?

Answer: If the monitored parameters that indicate proper operation of the NOx emission controls are not within the acceptable ranges for the entire hour, then you must report the appropriate default NOx emission rate from Table LM-2 for the entire hour.

References: § 75.19(c)(1)(iv)(H)

History: Added on September 28, 2020

Top of Page

« Return to Part 75 Monitoring Policy Manual