Alternative to EPA Method 9 - Field Validation of the Digital Opacity Compliance System (DOCS): Results from the One-Year Regulatory Pilot Study

摘要

The US Environmental Protection Agency's (EPA) Emission Measurement Center (EMC), in conjunction with EPA Regions VI and VIII, the State of Utah and the US Department of Defense (DoD), has conducted a series of long-term pilot and field tests to determine the accuracy and reliability of a visible opacity monitoring system consisting of a conventional digital camera and a separate computer software application for plume opacity determination. This technology, known as the Digital Opacity Compliance System (DOCS), has been successfully demonstrated at EPA-sponsored Method-9 'smoke schools' as well as at a number of government and commercially operated industrial facilities. Results from the current DOCS regulatory pilot study demonstrate that, under regulatory enforcement conditions, the average difference in opacity measurement between the DOCS technology and EPA Reference between the DOCS technology and EPA Reference Method 9 (Method 9) is 1.12%. This opacity difference, which was computed from the evaluation of 241 regulated air sources, was found to be statistically significant at the 99% confidence level. In evaluating only those sources for which a nonzero visible opacity level was recorded, the average difference in opacity measurement between the DOCS technology and EPA Reference Method 9 (Method 9) was 1.20%. However, in this case, the opacity difference was found to be not significant at the 99% confidence level, a finding that suggests that the two opacity measurement methods are statistically equivalent when measuring nonzero visible opacity emissions. The EMC has acknowledged the acute need for the development and promulgation of a new, scientifically defensible method for the measurement of visible opacity. The use of digital imaging/processing brings current technology to bear on this important regulatory issue.