Facility-Scale Emission Estimates: Approaches, Anecdotes, and Practical Considerations

Abstract:

Facility-scale emission estimates have been made using a variety of approaches and techniques which may employ measurements from several instruments. Measurements may be used alone or in combination, possibly within formalized methods. Direct measurements of single emission sources and indirect, downwind measurements of multiple emission sources are two commonly used approaches. Often, the chosen measurement approach is influenced by the desire for a large sample size to better characterize a population of facilities within a limited schedule and budget. This may have implications on the precision and accuracy of the resulting measurements, and thus the overall emissions estimate from the population of facilities measured. We have found that a multi-method approach is often useful and can help maximize the number of sites visited with minimal dilution of precision and accuracy. By having a suite of methods at the ready, the most appropriate method for the situation can be chosen and implemented efficiently thereby maximizing the number of successful measurements, minimizing the number of unmeasured sources, and reducing the uncertainty of each individual measurement. Here we discuss our experiences with a few approaches that have been used to characterize facility-scale emissions by ourselves and others. Approaches considered include onsite direct measurements (high volume sampling and exhaust gas sampling) and downwind measurements (OTM-33A and tracer release methods). We discuss the strengths, weaknesses, limitations, and operational challenges associated with each of these approaches and provide anecdotes from field experience.