The purpose of Procedure 2 is to establish the minimum requirements for evaluating the effectiveness of quality control (QC) and quality assurance (QA) procedures and the quality of data produced by particulate matter (PM) continuous emission monitoring system (CEMS). Procedure 2 applies to PM CEMS used for continuously determining compliance with emission standards or operating permit limits as specified in an applicable regulation or permit. Other QC procedures may apply to diluent (e.g., O2) monitors and other auxiliary monitoring equipment included with your CEMS to facilitate PM measurement or determination of PM concentration in units specified in an applicable regulation. Procedure 2 requires you to perform periodic evaluations of PM CEMS performance and to develop and implement QA/QC programs to ensure that PM CEMS data quality is maintained. We have recently become aware that facilities, especially those that have installed control devices, are having difficulty passing their annual QA/QC test because their emissions are lower than they were during the original testing. Procedure 2 currently contains a requirement that the annual QA/QC test results must fall within the same response range as was used to develop the initial correlation curve. We are proposing to modify Procedure 2, to remove the requirement that the response ranges be the same at the low end, so that facilities that have lowered their emissions and have results lower than their initial correlation testing are no longer being penalized.