You are here:
THE CHALLENGE OF QUALITY ASSURANCE FOR EMISSION FLUX MEASUREMENTS OF LARGE AREA SOURCES BY OPTICAL REMOTE SENSING
Citation:
Wasson*, S AND R. S. Wright. THE CHALLENGE OF QUALITY ASSURANCE FOR EMISSION FLUX MEASUREMENTS OF LARGE AREA SOURCES BY OPTICAL REMOTE SENSING. Presented at 22nd National Conference on Managing Environmental Quality, New Orleans, LA, 04/14-17/03.
Description:
The paper examines the quality assurance challenges associated with open path Fourier transform infrared (OPFTIR) measurements of large area pollution sources with plume reconstruction by computed tomography (CT) and how each challenge may be met. Traditionally, pollutant concentrations are measured by OPFTIR, then calculations involving concentrations, wind speed, and wind direction are performed to reconstruct the plume that provides estimates of the emissions flux, but in the last few years CT has gained popularity. Path integrated concentrations (PICS) are determined using multiple optical beam paths in the vertical and/or horizontal planes. Then a mathematical function is fitted to the measured PICS, and the spatial distribution of concentrations is generated for a plane perpendicular to the direction of the wind moving across the area source or horizontal above the source. Estimates of the emission flux are determined by integrating the product of the calculated concentrations and wind speeds over the plane. The quality assurance challenges arise because no standard method exists for the complete process. Although EPA has Compendium Method TO-16 for OPFTIR, project personnel are required to choose between several options without adequate guidance. Such choices include the concentration measurement device, the CT calculation methods required to arrive at the spatial distribution, and the mathematical method used to reconstruct the plume and the vertical wind field and to calculate the emission flux. Defensible estimates of the uncertainty of the final emission flux have not yet been developed. A data validation procedure is needed for the entire measurement and calculation process. Auditors are challenged to configure an adequate performance evaluation standard that is representative of a large area source.