Instrumental Method Substitutes for Visual Estimation of Equivalent Opacity

Many air pollution control regulations limit the emission of visible effluents, based on the visual observation of “equivalent opacity.” Because of difficulties encountered in using visual observation, the Texas Air Control Board developed a method of calibration which made it possible to use an instrumental method for measuring visible emissions. A legal regulation based on this instrumental method has been in effect for almost two years. Despite minor difficulties in calibration and maintenance, results have been satisfactory. The use of the instrumental method avoids many of the difficulties inherent in using a regulation based on visual observation, and continued use of the instrumental method is anticipated.