Digital Photographic Technique to Quantify Plume Opacity During Daytime and Nighttime

Abstract

United States Environmental Protection Agency (USEPA) developed opacity standards for sources of visible emissions to protect the visual quality of ambient air. Method 9 is USEPA’s standard method to quantify plume opacity by visual observations from qualified human observers during daytime. These observers are required to be certified twice a year at a “smoke school”. “Smoke school” is more formally referred to as “Visible Emissions Training”, which generally consists of a lecture session and a certification event where observers are field tested for their ability to determine the opacity of plumes. However, the use of observations by humans to quantify plume opacity introduces subjectivity, and is expensive due to semi-annual certification requirements of the observers. In addition, sources may emit plumes during nighttime that also need to be monitored to determine compliance for those sources. Digital Optical Method (DOM) was developed to quantify plume opacity from digital photographs for both daytime and nighttime conditions. Daytime field campaigns were completed during smoke schools with the Illinois Environmental Protection Agency (IEPA) and with industrial stacks during daytime. Field campaigns were also completed during nighttime with a smoke generator operated by IEPA. The field tests demonstrated that DOM has advantages when compared to Method 9 by its lower cost, improved objectivity, and availability of photographs of the visible emissions and their environments. Errors in results from DOM when compared to a reference in–stack transmissometer or a Method 9 observer are within USEPA’s error limits for Method 9. These encouraging results indicate that DOM has the potential to serve as an alternative method to Method 9 to determine the opacity of plumes for regulatory compliance of stationary sources.