NAC445B.262. Monitoring systems: Measurement of opacity.

     1. For continuous monitoring systems measuring opacity of emissions, the optical surfaces exposed to the effluent gases must be cleaned before performing the zero or span drift adjustments, except that for systems using automatic zero adjustments, the optical surfaces must be cleaned when the cumulative automatic zero compensation exceeds 4 percent opacity. Unless otherwise approved by the Director, the following procedures, as applicable, must be followed:

     (a) For extractive continuous monitoring systems measuring gases, minimum procedures must include introducing applicable zero and span gas mixtures into the measurement system as near the probe as is practical. Span and zero gases certified by their manufacturer to be traceable to National Institute of Standards and Technology reference gases must be used whenever these reference gases are available. The span and zero gas mixtures must be the same composition as specified in Appendix B of 40 C.F.R. Part 60. Every 6 months after the date of manufacture, span and zero gases must be reanalyzed by conducting triplicate analyses with Reference Methods 6 for SO₂, 7 for NO, and 3 for O₂ and CO₂, respectively. The gases may be analyzed at less frequent intervals if longer shelf lives are guaranteed by the manufacturer.

     (b) For nonextractive continuous monitoring systems measuring gases, minimum procedures include upscale checks using a certified calibration gas cell or test cell which is functionally equivalent to a known gas concentration. The zero check may be performed by computing the zero value from upscale measurements or by mechanically producing a zero condition.

     (c) For continuous monitoring systems measuring opacity of emissions, minimum procedures include a method for producing a simulated zero opacity condition and an upscale (span) opacity condition using a certified neutral density filter or other related technique to produce a known obscuration of the light beam. These procedures must provide a system check of the analyzer internal optical surfaces and all electronic circuitry, including the lamp and photodetector assembly.

     2. Notwithstanding the provisions of subsection 1, the Director shall not approve an alternative method or equivalent method to determine compliance with a standard or emission limitation contained in Part 60, 61 or 63 of Title 40 of the Code of Federal Regulations for:

     (a) An emission unit that is subject to a testing requirement pursuant to Part 60, 61 or 63 of Title 40 of the Code of Federal Regulations; or

     (b) An affected source.

     [Environmental Comm’n, Air Quality Reg. part § 2.17.4, eff. 12-4-76; § 2.17.4.1, eff. 12-4-76; A 12-15-77; §§ 2.17.4.2 & 2.17.4.3, eff. 12-4-76]—(NAC A by R065-03, 10-30-2003)