Figure 2‐2 Elements of a CEM rule.

      Public perception monitoring (or more euphemistically, “good neighbor” monitoring) refers to more stringent monitoring requirements established for sources such as municipal and hazardous waste combustors. In this case, extensive monitoring requirements are specified, coupled with plant operational interlock criteria where waste feed is shut off if emission limits should be exceeded. The continual oversight given by this instrumentation is intended to provide assurances to the public that environmental concerns associated with these types of sources are being addressed.

      In addition to addressing source categories, operational units, and monitoring purposes, implementing rules also specify source specific monitoring details, such as instrument span requirements, data conversion equations, averaging periods, quality assurance, and reporting requirements. These details are important for using the data, but are often overlooked, particularly in state permits. Although there is a greater awareness of the need to specify such requirements in the implementing rules, when they are not incorporated, the rule may be too ambiguous to fulfill its regulatory intent. The variety of implementing rules that require the installation of CEM systems are examined further in the following sections.

      U.S. Federal Implementing Rules

U.S. federal stationary source emissions standards and monitoring requirements are drafted by offices of the Environmental Protection Agency. The most important of these is the Office of Air Quality Planning and Standards (OAQPS), which developed the first CEM implementing rules and performance specifications in the early 1970s (U.S. EPA 1975). Other EPA offices have instituted CEM programs based on the original OAQPS regulations, modifying them for their own regulatory applications. Figure 2‐3 summarizes CEM regulatory programs that have been instituted.

      In the United States, rules are first developed by the respective office and proposed in the Federal Register (FR), a document published on each government business day that includes regulatory proposals, promulgations, notices, and discussions concerning the rulemaking. After public hearings, comment, and revision, the regulations and requirements are promulgated and adopted into the U.S. Code of Federal Regulations (CFR). The CFR is a multivolume compendium of U.S. regulations for federal government agencies, which is revised annually to incorporate any new rules or changes in existing rules. It is the principle reference for environmental regulation in the United States.

      Code of Federal Regulation citations are given in the format: (Title) CFR (Part). For example, 40 CFR 60 refers to the part of the code where the New Source Performance Standards (NSPS) are found. Performance specification test procedures for CEM systems are found in 40 CFR 60 Appendix B (U.S. EPA 2020c). Federal Register citations are given in the format: (Volume No.) FR (Page No.) (Date). As another example, the final performance specification test procedures 1–4 were published in the Federal Register in 1975 at 40 FR 46240 10/ 6/75. CFR publications can be found on http://www.ecfr.gov. Federal Register publications can be found on http://www.govinfo.gov/app/collection/fr. Federal Register publications can be useful by providing a background behind decisions that went into a final rule. Preambles to final rules include EPA’s responses to comments submitted on the proposed rule on which the final rule is based. Most of the rules do not stand alone and refer to other rules, test methods, monitoring specifications, and quality assurance requirements in other subparts and/or appendices of the Code of Federal Regulations.

      Once promulgated, implementing rules may be amended or superseded by subsequent rules. This can create some confusion, particularly when rules overlap, as has been the case with the acid rain rules of 40 CFR 75 and the New Source Performance Standards of 40 CFR 60. Because the source‐specific standards are written at different times by different people, the formats, terminology, and specifications are sometimes inconsistent between the different standards. Although there are periodic attempts to harmonize the rules, inconsistencies often remain.

       New Source Performance Standards, 40 CFR 60

      U.S. EPA regulations concerning stationary sources are found under Title 40 Subchapter C of the Code. Newly constructed sources are required to meet New Source Performance Standards (NSPS), which are given in Part 60 of Title 40 (expressed as 40 CFR 60). Each source category, such as the electric utilities, municipal incinerators, or cement plants, is assigned a Subpart letter (Subpart Da, Eb, and F, respectively) by which it is referred to in the CFR (U.S. EPA 2020a).

The rules prepared by this office affect newly constructed sources. A “new source” is defined as one constructed after the date the rules are first proposed in the Federal Register. An “existing source” is a source constructed before that date. Rules for existing sources are given by the individual states, usually in facility operating permits, with federal guidance and approval. The Part 60 Subparts address primarily new sources, but also include subparts that provide guidance to the states to develop rules for existing sources. When meeting the federal guidance requirements, the rules for specific source categories can be incorporated into the State Implementation Plan (SIP) (U.S. EPA 2020b). Source categories required to install CEM systems under NSPS are given in Table 2‐1.