For purposes of observing emissions in accordance with applicable provisions of the rules of the bureau, opacity (per cent) and shade or appearance (Ringelmann number) shall be determined visually by a certified observer. Opacity (per cent) is applicable to all plumes regardless of color. Shade or appearance (Ringelmann number) is applicable to gray and black plumes only. The resultant observation shall be the aggregate of individual readings.
N.J. Admin. Code § 7:27B-2.3