Accuracy Counts: Important Facts about the Accuracy of EPA Protocol Gases

The Environmental Protection Agency's Acid Rain Program, as defined under Title IV of the 1990 Clean Air Act Amendments, establishes a national cap on sulfur dioxide (SO2) emissions and targets reductions in both SO2 and oxides of nitrogen (NOx) emissions. To establish compliance, utilities and other industrial facilities must meet requirements for certification, daily calibration and ongoing quality assurance of continuous emissions monitoring systems (CEMS) used in the Acid Rain program.

If your facility is impacted by these regulations, you’ll want to take a closer look at the EPA protocol gases you use to calibrate your CEMS. You could be risking non-compliance and the expense of unnecessary RATA tests.

The EPA's 1997 protocol guidelines allow wide flexibility in how protocols are analyzed. For this reason, all EPA protocol gases are not created or analyzed equally.

Many gas suppliers promise +/- 1% accuracy, but delivery on this promise depends on critical choices they make during production.

Differences can be divided into three critical areas. Each can significantly impact the final accuracy of the EPA protocol gas you use to calibrate your CEMS.

Traceability: The EPA's protocol documents require that EPA protocol gases be traceable to: Standard Reference Materials (SRMs) and NIST-Traceable Reference Materials (NTRMs) provided by the National Institute of Standards and Technology (NIST); or Primary Reference Materials (PRMs) provided by the Netherlands Measurement Institute (NMi). Direct traceability to these materials ensures accuracy. Use of Gas Manufacturer Intermediate Standards (MGIS) can result in an unacceptable accuracy of beyond +/- 2%. Check your Certificates of Accuracy to see to which reference materials your protocols are anchored.

Analyzer Interference Resolution: To save time and money in calibration, auditing and cylinder handling without jeopardizing compliance, Acid Rain utilities often purchase multi-component EPA protocol gases. These are protocols with more than one pollutant component in a cylinder (e.g., sulfur dioxide, nitric oxide and carbon dioxide in nitrogen). Use of instrumentation that is interference-free during analysis of multi-component protocols is superior to mathematical corrections. Check your Certificates of Accuracy to see which method was used to prepare your multi-component protocols.

Choice of Protocol Procedures - Dilution vs. Nondilution: The EPA specifies two different procedures for preparing protocol gases. Procedure G1 requires direct comparison with a reference standard (SRM, NTRM, PRM or GMIS) without the use of a dilution device. Procedure G2 allows gas manufacturers to use dilution devices for comparison between the protocol gas being prepared and a reference standard. Diluting a standard (G2 analysis) adds uncertainty and is not as accurate as using a direct SRM, PRM or NTRM (G1 analysis). Check your Certificates of Accuracy to see which procedure was used to prepare your protocols.

The use of GMIS traceability, mathematical analyzer interference corrections and use of Procedure G2 can easily degrade accuracy when preparing EPA protocol gases. When used in combination, they can yield a total error in excess of 3% or more, which leads to regulatory non-compliance.

To avoid costly downtime, noncompliance fines, negative publicity and unnecessary RATA testing expenses, ask your supplier these important questions before you purchase another EPA protocol gas for your environmental measures:

• What kind of reference standards do you typically analyze against? NTRMs, SRMs or PRMs to achieve direct NIST traceability, or against GMISs which may have too much uncertainty to create a truly accurate mixture?
• How does your laboratory resolve interference effects in multi-component protocols? (Ask your supplier to show you how multi-component analysis interferences are avoided.)
• Which "no interference" technology do you use when preparing multi-component protocol mixtures? (Ask your supplier to supply backup analytical data.)
• Which protocol procedure does your laboratory use to certify protocol gases? Procedure G1, without dilution is ideal. Procedure G2 should be used only when a NIST SRM, NTRM or PRM is not available.
• Do you participate in NIST NTRM programs? Suppliers who don't may not always be able to provide directly traceable EPA protocol gases.
• What is your lead time for manufacturing a protocol gas? Lead times longer than 12 to 18 calendar days may suggest inefficient production processes or inadequate reference standard inventories.
• What information do you provide on your Certificates of Accuracy and labels? (Examine examples of documentation and compare them with EPA requirements to ensure accuracy and completeness.)
• Do you provide other critical services that can help ensure regulatory compliance? Inventory management, on-site evaluations and needs assessment services can help eliminate all primary reasons why utilities fail environmental audits.

By applying these standards in your selection of EPA protocol gases, you can maximize the efficiency and accuracy of your CEMS and potentially push your performance far beyond the 10% requirement of the EPA's Acid Rain Program.

About Air Liquide America Specialty Gases

Air Liquide America Specialty Gases (formerly, Scott Specialty Gases) is known as the leading international producer and supplier of pure and mixed specialty gases for all types of applications as well as the world’s largest producer of EPA protocol gases. Air Liquide America Specialty Gases is respected and trusted not only for its pures and mixtures, but for its high-performance gas handling equipment and specialty gas delivery and monitoring systems. More information on the company and its products can be found at http://www.scottgas.com.