General Approach to Estimating Air Pollutant Sources Based on Observations of Concentrations and Winds
Steven Hanna
Hanna Consultants, 7 Crescent Ave., Kennebunkport, ME 04046-7235
(207 967 4478, hannaconsult@roadrunner.com)
The intent of this paper is to show that the source term estimation model systems in use by many agencies for many purposes, and described using different terminology, have less differences than first thought. The various agencies’ approaches to source term estimation for their scenarios of interest, using observations of concentrations and winds, are described. For example, the DOD and DHS are usually concerned with quickly determining the location and magnitude of a toxic gas release by a terrorist at a large public gathering, the EPA is often concerned with quantifying the mass emission rates at specific industrial or agricultural facilities, and the climate community is often concerned with more accurately estimating the emissions of greenhouse gases over a broad area. As the numbers of unknowns increase, and as the weather becomes more variable, the accuracies of the source term estimates decrease. Generalized approaches are suggested for statistical optimization processes and for transport and dispersion (T&D) modeling, and use of the DOD Fusion Field Trial 2007 (FFT2007) field observations is suggested for model development and testing. As Gifford (1959) showed, the same T&D model can be run in a backwards or forwards direction, with the resulting probability distributions interpreted differently (i.e., probability of the source mass being found at a certain location and time in the forward direction, and probability of the source being at a certain location and time in the backwards direction). It is further suggested that, to optimize use of resources and to more efficiently advance the field, collaborations among agencies should be implemented and approaches and terminology harmonized.
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