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.

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