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What Is RATA Testing?
Understanding the role of a Relative Accuracy Test Audit in emissions monitoring, CEMS certification, and defensible compliance data.
RATA Testing Explained
RATA stands for Relative Accuracy Test Audit. In plain terms, it is a field test that compares the data from a facility’s continuous emissions monitoring system, often called a CEMS, against results from approved reference test methods collected at the same time.
The goal is not only to produce a percentage on a report. RATA testing helps confirm that the monitoring system, sample conditioning equipment, data acquisition and handling system, and field procedures are working together well enough to support regulatory compliance.
What Is RATA Testing?
RATA testing is a structured accuracy check for emissions monitoring systems. During the test, a qualified stack testing team collects reference method data while the installed monitoring system records its own readings. Those paired results are then evaluated to determine whether the installed system is reporting within the required relative accuracy limits.
Requirements vary by permit, pollutant, unit type, and applicable rule, but RATA programs are commonly associated with CEMS certification, recurring quality assurance, recertification after system changes, and emissions compliance programs under EPA and state requirements.
Quick definition: A RATA compares CEMS readings to reference method results so a facility can demonstrate that its emissions monitoring data is accurate enough for compliance use.
When Is RATA Testing Required?
Facilities typically plan RATA testing when a monitoring system is first certified, on a recurring QA schedule, after significant repairs or modifications, or when a regulatory program, permit, consent order, or agency request calls for a new accuracy demonstration.
Common applications include SO2, NOx, CO2, O2, flow, moisture, mercury, and other systems depending on the regulation and the facility’s permit conditions.
- Initial CEMS certification or new monitor startup
- Annual or semiannual quality assurance programs
- Recertification after significant CEMS or DAHS changes
- Permit-driven or agency-requested performance checks
- Corrective action follow-up after failed QA testing
How a RATA Works
The exact test plan depends on the applicable rule and permit, but a typical RATA follows a disciplined sequence:
- Confirm the test basis. Review the applicable permit, regulation, monitoring plan, operating level, and reference method requirements.
- Prepare the CEMS and DAHS. Confirm calibration checks, data alignment, time synchronization, and sample system readiness before the test window.
- Collect paired data. Perform reference method runs while the installed monitoring system records simultaneous data.
- Calculate relative accuracy. Evaluate the paired data using the required equations and acceptance criteria for the monitor and program.
- Document and report results. Assemble the final package for certification, QA records, agency submittals, and follow-up corrective action when needed.
Why RATA Results Matter
Emissions data can influence compliance status, reporting obligations, operating decisions, and agency confidence. A passing RATA helps show that reported emissions are supported by field evidence. A failed or poorly prepared RATA can lead to retesting, data substitution, corrective work, reporting delays, or additional scrutiny.
Data Confidence
Supports credible emissions reporting with a documented comparison to reference methods.
Operational Readiness
Reveals monitor, sample handling, calibration, or DAHS issues before they interrupt compliance workflows.
Clear Documentation
Creates a stronger record for audits, agency review, and future quality assurance planning.
Benefits of a Strong RATA Program
1. Regulatory Confidence
A well-run RATA creates a defensible record that the monitoring system has been tested against required reference methods.
2. Lower Retest Risk
Pre-test checks, clean data handling, and coordinated field execution reduce the chance of avoidable failures.
3. Better System Reliability
RATA preparation often reveals analyzer drift, sample transport issues, flow measurement concerns, or DAHS configuration problems before they become larger compliance issues.
4. Cleaner Reporting
When monitoring, testing, and data teams are aligned, final reports are easier to review, defend, and submit.
5. Smarter Maintenance Planning
RATA trends can help teams prioritize analyzer service, calibration strategy, probe maintenance, and sample conditioning improvements.
Some Real-World Examples of RATA Testing in Action
- Power generation CEMS: A facility schedules annual RATA work to verify NOx, SO2, CO2, O2, and flow monitoring performance before compliance reporting deadlines.
- Refining and petrochemical operations: A site uses RATA planning to coordinate unit load, stack access, analyzer readiness, and DAHS data validation around tight operating windows.
- Cement and aggregate plants: A plant verifies emissions monitoring performance while also reviewing sample system condition and calibration practices.
- System modification projects: After analyzer replacement, DAHS updates, or probe changes, a RATA may be part of the recertification path.
Looking for Related Emissions Services?
TriCore IMS supports the full emissions monitoring lifecycle, from analyzer engineering and DAHS integration through QA planning, RATA support, and corrective action.
Get Started with RATA Testing Services
Your RATA should support the full compliance picture, not just a test date on the calendar. TriCore IMS helps facilities prepare, execute, troubleshoot, and document RATA programs with engineering discipline and practical field experience.
Schedule a consultation to review your monitoring system, upcoming test window, or RATA corrective action plan.