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To this point, we have discussed implementing rules for CEM systems, rulemaking requiring the installation of a CEM system on a source category or a specific unit of a source. The implementing rule, however, is not complete unless it refers to some procedure that can be used to verify that the installed CEM system can provide data at a specified level of accuracy and precision. The level of accuracy can vary with the rule, depending upon the pollutant and the purpose of the rule. However, some verification procedure must be established so that the installed system can be shown to provide emissions data suitable to meet the purposes of the implementing rule.

In the United States, the verification or certification procedures established for CEM systems are given in standards called “performance specifications.” The performance specifications include requirements for the installation, design, performance, and testing of CEM systems. The installation criteria are regulatory guidelines for identifying measurement locations where representative measurements can be expected. Design specifications require that the instruments must be designed in a certain manner. These are important and specified in detail for opacity monitors, but are minimal for gas monitors.

The specifications for the performance of the monitoring systems are the most important part of these standards (except for opacity monitors, where the design specifications predominate). Specifications are given for drift, relative accuracy, and, in some cases, linearity. Basically, the design of a gas monitoring system is not relevant to the specifications. It does not matter whether the system is extractive or in‐situ or if the method of measurement is electro‐optical or electrochemical. It does matter, however, how the system performs. The proof of a system is in its performance as installed. The performance specification test procedures are applied to demonstrate that the installed CEM system meets “performance specifications.” If a CEM system meets these specifications, it is considered capable of providing quality data for the purpose of the implementing rule.

Sixteen sets of performance specification have been established for pollutant and diluent gas flow and particulate monitoring systems for sources subject to the New Source Performance Standards. Sources are required to meet these specifications after an applicable monitoring system has been installed or when otherwise called out by a rule. The NSPS specifications are found in Appendix B of 40 CFR 60. Other specifications are given for other implementing rules, and the states may write their own performance specifications (e.g. Pennsylvania and California). The Code of Federal Regulations citations where performance specifications for other implementing rules can be found are given in Table 2‐4.

As noted, EPA does not approve specific brands of instrumentation or specific analytical methods (in the case of gas monitoring) for source monitoring systems. This is in contrast to the policy of approving specific instrument models for continuous ambient air analysis. The procedure of meeting performance specifications provides latitude in continuous monitoring system design and application by allowing sources to handle individual monitoring problems. Since stack conditions vary from plant to plant, a CEM system found to work well at one plant may not work at another. Vibration, heat, or other conditions may necessitate a careful analysis of available monitors and systems before one can be chosen for the job. The performance specifications define the procedures to be used for checking the installed instrument's performance. It is the installed instrument system, operating on the stack, that is approved, not the model.

TABLE 2‐4 Performance Specifications for U.S. EPA Implementing Rules

Originating EPA Office	Program	Citation for Implementing Rule Performance Specifications
OAQPS	NSPS	40 CFR 60 Appendix B
OAQPS	Air toxics	40 CFR 63.8 monitoring requirements
OAR‐ARD	Acid rain	40 CFR 75 Appendix A
OSW	Boilers and industrial furnaces	40 CFR 266 Appendix IX
OWM	Sewage sludge incinerators	40 CFR 503 Subpart E

U.S. CEM system certification procedures differ from those instituted in the European Union, where CEM system analyzers must undergo “type” testing, both in the laboratory and field, to show that they meet the design and performance specifications of the EU standard EN 15267. However, it has been found that a CEM system accredited under EN 15267 does not necessarily guarantee that it will pass a U.S. Performance Specification Test after installation.