What is a Relative Accuracy Test Audit?
Relative Accuracy Test Audits (RATAs) are critical for validating the accuracy of Continuous Emission Monitoring Systems (CEMS). Conducted annually or every four QA operating quarters (168 operating hours or more), these audits compare the emissions data collected by CEMS against reference methods performed by certified stack testers. The goal is to ensure data used for compliance and reporting is both accurate and reliable.
Frequency and Regulatory Requirements
Part 75 RATA Testing
Part 75 primarily applies to electric generating units (EGUs) and other large sources subject to the Acid Rain Program, the Cross-State Air Pollution Rule (CSAPR), and other emissions trading programs. The main pollutants monitored under Part 75 include sulfur dioxide (SO2), nitrogen oxides (NOx), carbon dioxide (CO2), and oxygen (O2).
Regulatory References:
- Appendix A, §§ 3.3 and 6.5
- Appendix B, § 2.3.1
- Part 75 Policy Manual, Section #8 (Relative Accuracy)
Part 60 RATA Testing
Part 60 applies to a broader range of stationary sources, including industrial facilities, manufacturing plants, and other non-EGU sources. This part establishes New Source Performance Standards (NSPS) for various pollutants, including particulate matter (PM), volatile organic compounds (VOCs), and hazardous air pollutants (HAPs).
Regulatory References:
- Appendix F – Procedure 1, Section 5.1 (Auditing Requirements)
- Appendix B, Performance Specifications:
- Specification 2: SO2 & NOx
- Specification 3: O2 & CO2
- Specification 4: CO
Dual Compliance Challenges
Many facilities must comply with both Part 75 and Part 60 monitoring and reporting regulations. Often, the same CEMS are used to satisfy both sets of requirements, which can be challenging due to conflicting Quality Assurance tests and standards. Typically, the Title V Operating Permit outlines the requirements for RATAs under both Part 60 and Part 75 separately. However, it often specifies that conducting the RATA according to Part 75 standards is acceptable for Part 60 reporting. If this is not clearly stated in your permit, it is important to check with your local regulatory authority. Additionally, ensure that your in-house procedures for performing RATAs address this requirement.
Pre-RATA Planning Checklist
Follow these steps before you perform your RATA to properly plan and avoid errors on the day of testing.
1. Determine When RATAs Are Due
- Review your facility’s in-house RATA procedures.
- Generate a QA Test Status Report
2. Verify Operating Quarters
- Each of the last four quarters must have at least 168 operating hours.
3. Identify Load Requirements
- Flow RATAs must occur in each of three load ranges every five years, separated by at least 25% of the operating range.
- Gas RATAs must occur at one of the two most frequently operated load ranges.
- For more on load analysis, read our blog post.
4. Schedule and Notify
- Schedule RATA testing well in advance (weeks or months).
- Submit notification letters to EPA and local agencies at least 21 days in advance (unless exempt under §75.61(a)).
Day of RATA Test Best Practices
Follow these steps the day of your RATA to monitor and collect your data.
1. Confirm Steady-State Operation
Operate at high and stable load (90%+ of max load preferred).
2. Complete Preventative Maintenance
- Ensure all pollution control and CEMS equipment is serviced.
- Read our blog post “5 Tips to Help You Maintain Your CEMS” for tips and best practices.
3. Review Internal Procedures
Be prepared to explain the testing process to both operators and testers.
4. Conduct Stratification and Traverse Testing
- Stratification test determines proper sampling points (Part 75 Appendix A §6.5.5–6.5.6.1).
- Flow RATAs require traverse points selected per Appendix A and Method 1 (Part 60).
5. Monitor and Compare Results
- Exchange and compare results with stack testers every 2–3 runs.
- After 6–7 runs, evaluate if 10 runs are needed to reduce RA below 7.5%.
- Minimum of 9 runs required under Part 75; ESC Spectrum recommends 10.
- Review test results and documentation carefully—resolve any discrepancies with your testing contractor.
Post-Test Tasks and Data Management with StackVision
Our StackVision Data Acquisition System (DAS) works in tandem with the 8864 Data Controller to collect, monitor, QA, and report on emissions data from continuous monitoring systems accurately and reliably. Follow these steps after your RATA test concludes to smoothly and successfully report your data.
1. Gas Cylinder Reporting
- Report calibration gas cylinder usage in QA EDR.
- Upload gas certification sheets in StackVision’s Cal Gas Manager.
2. Identify the Qualified Individual (QI)
- Ensure QI details are recorded in StackVision (AETB tab).
3. Finalize and Enter RATA Results
- Enter data into StackVision and/or ECMPS.
- Use StackVision’s “Optimize” tool to select lowest RA set.
- Lock your RATA database using StackVision’s “Data Locking Wizard” to prevent accidental changes.
4. Reprocess Hourly Data
- If Bias Adjustment Factors (BAFs) change, reprocess hourly, daily, and YTD totals as required.
5. Submit QA EDR File
- Generate QA EDR file and run it through ECMPS.
- Resolve all errors before finalizing the report.
- Submit any required testing plans to agencies at least 4 weeks in advance.
How ESC Spectrum Can Help with Your RATA
To successfully perform Relative Accuracy Test Audits, it is important to ensure that your systems and tools are being used to their full potential. ESC Spectrum offers a variety of products and services to streamline your RATA Process, including the following:
- StackVision DAS and 8864 Data Controller to collect, monitor, QA, and report on RATA data.
- DASProtect maintenance plans, which offer round-the-clock support and regulatory and reporting services to assist with your EDRs.
- CEMS Maintenance Plans featuring RATA support.
- CEMSProtect Partner Program with customizable support.
Interested in learning more about regulations and staying in compliance? Read our Definitive Guide to Air Emissions Regulations.
Whatever your needs may be, ESC Spectrum is committed to assisting you through the RATA testing process.
Emma Fields | Regulatory & Reporting Engineer I
Emma Fields joined ESC Spectrum in May 2024, following her tenure as an Environmental Specialist with the Florida Department of Environmental Protection (FDEP). Her responsibilities include EPA and State Reporting Assistance, Emissions Data Report (EDR) Generation, and comprehensive data reviews to proactively identify and address potential issues. Emma's experience at the FDEP has equipped her with a thorough understanding of environmental laws, regulations, and compliance practices. Emma holds a Bachelor's Degree from the University of West Florida, where she established a strong foundation for her career in environmental protection and regulation.
