Historically, assessments of T&D models have involved comparisons to field trial data using quantities derived from
observations – maximum concentrations, plume widths, or integrated concentrations over arcs at various downwind ranges.
Recently several methodologies that compare observations and predictions paired in space and time have been developed. Two
different protocols designed to deal with low observed or predicted values have emerged. One of these protocols requires that both
the observation and the prediction must exceed a specified threshold before being considered in the comparison. The other protocol
requires that either the observation or the prediction must exceed a specified threshold before being considered in the comparison.
This presentation compares the potential effects of applying these two protocols to T&D model assessments
