Use of Digital Imaging/Processing as a New Method for Opacity Compliance Monitoring

摘要

The US Environmental Protection Agency' s (EPA) Emission Measurement Center (EMC) inconjunction with EPA Regions VI and VIII, the State of Utah and the US Department of Defense(DoD) have conducted a series of long-term pilot and field tests to determine the accuracy andreliability of a visible opacity monitoring system consisting of a conventional digital camera and aseparate computer software application for plume opacity determination. This technology, knownas the Digital Opacity Compliance System (DOCS), has been successfully demonstrated at EPAsponsoredMethod-9 "smoke schools" as well as at a number of government and commerciallyoperated industrial facilities.In Phase I, the DOCS technology was field tested under controlled demonstration conditions atEPA-approved smoke schools located in Ogden, UT, Augusta, GA and Columbus, OH. Thesefield tests demonstrated that the DOCS consistently met, and, in many cases exceeded, the federallycodified Method 9 performance standards. These field demonstration tests also revealed that theDOCS technology exhibited several important practical advantages for regulated facilitiesincluding: 1) improved measurement objectivity and reliability, 2) lower deployment andmaintenance costs and 3) generation of a permanent digital image of visible opacity that can beeasily referenced in challenging regulatory enforcement actions.During Phase II, the DOCS technology was evaluated at 241 government and private commercialsites under regulatory enforcement conditions. The average difference in visible opacity measuredbetween the DOCS technology and Method 9 using the entire data set was small (1.12%), a findingthat demonstrates that accuracy and reliability of the two opacity measurement systems arecomparable. Moreover, when only those air sources characterized by a nonzero visible opacitywere considered, the average visible opacity difference between the two approaches was determinedto be 1.20%. Statistically, this difference was found to be insignificant, a finding that supports theconclusion that the accuracy of the two opacity measurement approaches is equivalent. Finally, afield validation test of new digital camera models was conducted in support of the DOCStechnology. Field results demonstrated that the digital photographs taken by Kodak modelDX6490, Sony Cybershot DSC-WI and the Nikon Coolpix 5200 digital cameras generated highlyaccurate determinations of visible opacity when used in conjunction with the DOCS technologysoftware. Although the Fuji Finepix E500 generated digital photographs whose visible opacity, onaverage, was by approximately 2.2% less than the determinations from other digital cameras,additional testing will be conducted to determine if optical adjustments can be made to improve itsperformance.