5.1 Continuous opacity monitors are required to be installed at many stationary sources of air pollution by federal, state, and local air pollution control agency regulations. EPA regulations regarding the design and performance of opacity monitoring systems for sources subject to “Standards of Performance for New Stationary Sources” are found in 40 CFR 60, Subpart A General Provisions, §60.13 Monitoring Provisions, Appendix B, Performance Specification 1, and in applicable source-specific subparts. Many states have adopted these or very similar requirements for opacity monitoring systems.5.2 Regulated industrial facilities are required to report continuous opacity monitoring data to control agencies on a periodic basis. The control agencies use the data as an indirect measure of particulate emission levels and as an indicator of the adequacy of process and control equipment operation and maintenance practices.5.3 EPA Performance Specification 1 provides minimum specifications for opacity monitors and requires source owners or operators of regulated facilities to demonstrate that their installed systems meet certain design and performance specifications. Performance Specification 1 adopts this ASTM practice by reference so that manufacturers can demonstrate conformance with certain design specifications by selecting and testing representative instruments.5.4 Experience demonstrated that EPA Performance Specification 1 prior to the Aug. 10, 2000 revisions did not address all of the important design and performance parameters for opacity monitoring systems. The additional design and performance specifications included in this practice are needed to elimi