Digital Opacity Method
ERDC-CERL and University of Illinois (UI) have developed a new plume opacity measurement technology known as Digital Optical Method (DOMTM). DOMTM estimates the opacity of plumes in the out door ambient environment by analyzing digital images that are produced by off-the-shelf digital cameras. Airborne particulate matter causes light extinction due to its ability to absorb and scatter light. Opacity is expressed as the percent of light that is attenuated by the plume. DOMTM includes both contrast and transmission models that are based on light extinction theory to calculate plume opacity. Air permit holders and facility operators are required to measure/monitor opacity from their stationary air pollution sources. Presently, the ASTM standard for monitoring is US Method 9 which relies on human visual perception to measure opacity. The DOMTM method provides improved consistency and accuracy of the measurements, and permits retention of a digital record of the event.
Method 9 is costly because plume readers are required to be certified and then re-certified every 6 months at smoke schools in every State. The validity, accuracy and precision of Method 9 are often challenged in court cases, partially because of the reliance on smoke reader's subjective testimony. US Environmental Protection Agency (EPA) Office of Air Quality Planning and Standards estimated that total opacity compliance costs were close to $200 million/year. These costs include sending personnel to the certification school for 2-3 man days plus tuition and travel, and frequent recertifications. If DOMTM technology is used throughout the entire US, the labor savings will be significant and opacity disputes in court cases will be substantially reduced. For the US Army alone, DOMTM is expected to save multi-million dollars annually.
In addition to industrial plume monitoring, DOMTM also has been tested under the SERDP program to measure dust generated by military operations. The measurement of fugitive emissions can provide value for border and fenceline security applications.
DOMTM has completed TRL 7 with system prototype demonstration in operational environments. It remains to be commercially packaged and to achieve EPA official adoption.
The advantages of using DOMTM over Method 9 in opacity measurements include the reduction of labor costs, improved accuracy, reliability and objectivity, minimized litigation, and enduring records in the form of digital photographs.