Mercury emissions monitoring can feel like a complicated maze of regulations and technical steps, but at its core, it’s about ensuring cleaner air and safer communities. Two of the most important tools in this process are EPA Method 30B and the Relative Accuracy Test Audit (RATA). Method 30B lays out how mercury is measured, while RATAs make sure monitoring systems are working as intended. In this article, we’ll break down what these methods mean, how they work, and why they matter for compliance under the Mercury and Air Toxics Standards (MATS) and National Emission Standards for Hazardous Air Pollutants (NESHAP).
What is Method 30B?
Method 30B is an EPA-approved procedure for measuring total vapor phase mercury (Hg) emissions from coal-fired combustion sources. It uses sorbent trap sampling combined with either extractive or thermal analysis techniques. Method 30B is required for performing RATAs on mercury Continuous Emission Monitoring Systems (Hg CEMS) or sorbent trap systems, as well as for emissions testing of coal-fired boilers, NSPS compliance, NESHAP compliance, emissions trading, SIP requirements, and operating permits.
Basics of Method 30B Sampling
Sampling with Method 30B involves paired sorbent traps inserted directly into the stack gas stream. The system includes sorbent traps, probes, moisture removal devices, vacuum pumps, gas flow meters, flow controllers, thermocouples, and barometers for standardizing volumes. Only NIST-certified or traceable standards may be used for calibration. The method requires at least nine valid sampling runs, which typically include three spiked traps for field recovery testing.
Stratification Testing and Method 30A Reference
Method 30A provides the framework for determining sampling sites and points. For mercury emission testing, 3 traverse points are used unless stratification testing demonstrates otherwise. Depending on the degree of stratification, the number of sampling points can be reduced. For example, if concentrations vary by less than ±5% across the stack, sampling can be conducted at a single point. A stratification exemption may apply if concentrations are expected to be ≤3 µg/m³, provided at least one hour of data confirms this prior to testing.
8.1.3.2 Note for stratification exemption see Sect 8.1.3.4 of Method 30A
8.1.3.2.1 If HG concentration at each traverse point differs from the mean concentration for all traverse points by no more than: ± 5 percent or (± .2 ug/m3 ) whichever is less than the gas stream is considered to be un-stratified and you may collect samples from a single point that most closely matches the mean.
8.1.3.2.2 If HG concentration at each traverse point differs from the mean concentration for all traverse points by no more than: ± 10 percent or ( ± 0.5 μg/m3) whichever is less than the gas stream is considered to be minimally stratified, and you may take samples from three points, provided the points are located on the measurement line exhibiting the highest average Hg concentration. Also if the stack diameter is greater than 7.8 ft, locate the three sampling points at 0.4, 1.0, and 2.0 meters from the stack or duct wall.
8.1.3.2.3 If the gas stream is found to be stratified because the 10 percent or 0.5 μg/m3 criteria listed in section 8.1.3.2.2 is not met, then either locate three sampling points at 16.7, 50.0, and 83.3 percent of the measurement line that exhibited the highest average Hg concentration during the stratification test, or locate twelve traverse points for the test in accordance with Table 1-1 or Table 1-2 of Method 1 in appendix A to this part; or, if a RATA required by part 75 of this chapter is being conducted, locate six Method 1 points along the measurement line that exhibited the highest average Hg concentration.
Method 30B QA/QC Requirements
Method 30B includes strict QA/QC procedures to ensure valid results. Key requirements include:
- Analytical Matrix Interference Test (if using wet chemical digestion)
- Determination of minimum sample mass and calibration range
- Hg⁰ and HgCl₂ Analytical Bias Tests
- Field Recovery Tests with spiked samples (recoveries must be 85–115%)
- Leak checks (≤4% leak rate)
- Pre- and post-test calibration checks of flow meters and sensors
- Chain of custody documentation and proper sample handling
All sorbent trap analyses must fall within the calibrated range of the analytical system. Failure to meet QA/QC acceptance criteria may invalidate runs.
Relative Accuracy Test Audit (RATA) Requirements
RATAs ensure the accuracy of Hg CEMS or sorbent trap monitoring systems by comparing them to reference methods such as Method 29, Method 30A, Method 30B, or ASTM D6784-02 (Ontario Hydro). At least nine valid test runs must be performed, although up to 12 may be conducted with up to three discarded. For Method 30B, the minimum run time is 30 minutes for RATA and 1 hour for emissions testing. Results must meet the relative accuracy criteria of ≤20% or an absolute difference of ≤1.0 µg/scm. RATA results must be reported to EPA’s CDX system within 60 days of completion.
Special Considerations
Under 40 CFR Parts 60 and 63, both Hg CEMS and sorbent trap systems must be operated in compliance with Performance Specification 12B and Procedure 5 QA requirements. Facilities must conduct RATAs at normal operating conditions (e.g., with raw mills on at cement plants). Recertification is required if equipment or process changes significantly affect measurements. Cement plants under NESHAP must submit RATA data electronically through EPA’s CEDRI system within 60 days of testing.
A minimum of nine valid test runs must be performed, directly comparing the CEMS measurements to the reference method. More than nine test runs may be performed. If this option is chosen, the results from a maximum of three test runs may be rejected so long as the total number of test results used to determine the relative accuracy is greater than or equal to nine; however, all data must be reported, including the rejected data.
The minimum time per run is 21 minutes if Method 30A is used. If Method 29, Method 30B, or ASTM D6784–02 (Reapproved 2008), ‘‘Standard Test Method for Elemental, Oxidized, Particle-Bound and Total Mercury in Flue Gas Generated from Coal-Fired Stationary Sources (Ontario Hydro Method)’’ (incorporated by reference, see section 63.14) is used, the time per run must be long enough to collect a sufficient mass of Hg to analyze. Complete the RATA within 168 unit operating hours, except when Method 29 or ASTM D6784–02 is used, in which case up to 336 operating hours may be taken to finish the test.
Keys to a Successful RATA
- Before starting your RATA, validate that the analyzer is ready to go by using an audit trap (or two).
- Use well-maintained Method 30B sampling systems and calibrated analyzers.
- Ensure analysts are experienced with Method 30B and PS12B.
- Develop and review test plans with plant personnel in advance.
- Review plant Hg concentration data to calculate appropriate spike levels.
- Order sorbent traps (30B & PS12B) well in advance of testing.
- Verify CEMS are in total mode and disable calibration and automated blowback prior to performing a RATA.
Conclusion
EPA Method 30B and RATA requirements form the backbone of mercury compliance monitoring for coal-fired power plants, cement manufacturers, and other industrial facilities regulated under federal air quality standards. By following QA/QC protocols, preparing test plans, and maintaining monitoring systems, facilities can ensure accurate measurements and meet federal reporting requirements. For guidance, technical support, or help ordering sorbent traps, feel free to contact us – we specialize in Method 30B systems and compliance solutions.
Tools to Make Compliance Easier
If you’re already starting to plan for next year’s compliance testing, now is the perfect time to think about your supply and equipment needs. At Ohio Lumex, we provide instruments designed specifically to simplify Method 30B testing and mercury RATA compliance:
- Sorbent Traps – Our 30B and PS12B sorbent traps are manufactured with zero-background carbon and individually numbered for accuracy and traceability. They are available in configurations tailored to your stack conditions, ensuring reliable results in both wet and dry environments.
- M324 Sorbent Trap Analysis System – Designed for laboratory analysis of Method 30B sorbent traps, the M324 provides accurate, high-throughput measurements to support QA/QC requirements.
By pairing proven testing methods with the right instruments, facilities can stay compliant and streamline their mercury monitoring programs.
