The United States Environmental Protection Agency (USEPA) developed Method 9 to describe how plume opacity can be quantified by humans. However, use of observations by humans introduces subjectivity, and is expensive due to semiannual certification requirements of the observers. The Digital Opacity Method (DOM) was developed to quantify plume opacity at lower cost, with improved objectivity, and to provide a digital record. Photographs of plumes were taken with a calibrated digital camera under specified conditions. Pixel values from those photographs were then interpreted to quantify the plume's opacity using a contrast model and a transmission model. The contrast model determines plume opacity based on pixel values that are related to the change in contrast between two backgrounds that are located behind and next to the plume. The transmission model determines the plume's opacity based on pixel values that are related to radiances from the plume and its background. DOM was field tested. Results are encouraging and support the use of DOM as an alternative to Method 9.

This project was funded by the US Army Corp of Engineers Construction Research Laboratories. My findings on this topic are presented through three papers. We have submitted one patent application for this method. An ASTM working committee ("Digital Opacity Optical Method to Quantify Ambient Plume Opacity", Work Item No. WK11380) has been organized to standarize our DOM technology.  

Smoke generator at the Illinois EPA smoke school

Schematic describing the contrast (A) and transmission (B) models to determine plume opacity.

DOM Publications

DOM principles, and methodology development
Du, K., Rood, M. J., Kim, B. J., Kemme, M. R., Franek, B., and Mattison, K. (2007) Quantification of Plume Opacity by Digital Photography, Environmental Science and Technology, Vol. 41, No. 3, 928-935.

DOM applications in the field under various conditions
Du, K., Rood, M. J., Kim, B. J., Kemme, M. R., Franek, B., Mattison, K. and Cook, J. (2007) Evaluation of Digital Optical Method to Quantify the Visual Opacity of Plumes in the Field, Journal of Air and Waste Management Association, Manuscript accepted for publication, pp. 25.

DOM principles and applications during nighttime
Du, K., Rood, M. J., Kim, B. J., Kemme, M. R., Franek, B., and Mattison, K. (2007) Quantification of Plume Opacity from Stationary Point Sources Using Digital Imaging Technology during Nighttime, manuscript in preparation for Environmental Science and Technology.

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