N.J. Admin. Code § 7:27B-2.1
The following words and terms, when used in this Subchapter, shall have the following meanings, unless the context clearly indicates otherwise. Terms not defined in this Section are intended to be used as defined in the New Jersey Air Pollution Control Act, N.J.S.A. 26:2C-1 et seq. and Chapter 27 in Title 7 of the New Jersey Administrative Code, or are used in their common engineering or scientific sense.
"Bureau" means the Bureau of Air Pollution Control.
"Department" means the Department of Environmental Protection.
"Opacity" means the property of a substance which renders it partially or wholly obstructive to the transmission of visible light expressed as the percentage to which the light is obstructed.
"Ringelmann number" means a number used to describe the density of smoke as determined from the Ringelmann smoke chart.
"Ringelmann smoke chart" means the "Ringelmann scale for grading the density of smoke" as published by the United States Bureau of Mines or any chart, recorder, indicator or device which is approved by the Department as the equivalent of the Ringelmann scale for the measurement of smoke density.
N.J. Admin. Code § 7:27B-2.1