Documentation of the Evaluation of CALPUFF and Other Long ...

2.3.3 Comparison of CALPUFF Modeling Results to Two Tracer Field Experiments
The CALPUFF dispersion model (CALPUFF Version 4) was compared against tracer
measurements from the GP80 and SRL75 field study experiments in a study conducted by
James O. Paumier and Roger W. Brode (EPA, 1998a). The evaluation approach adopted the
method used by Irwin (1997) that examined fitted predicted and observed plume
concentrations across an arc of receptors. Meteorological inputs for the CALPUFF model were
based on CALMET using observed surface and upper‐air meteorological data. The study found
that for these three tracer releases, there was overall agreement between the observed times
and modeled times for both the time required for the plume to reach the receptor arc, as well
as the time to pass completely by the arc. However, the transport direction had an angular
offset. For the GP80 100 km arc, CALPUFF underestimated the lateral dispersion of the plume
and overestimated the plume peak as well as the cross wind integrated concentration (CWIC)
average concentrations across the plume; the lateral dispersion and CWIC were within a factor
of two of the observed value and the CALPUFF fitted plume centerline concentrations was 2 to
2½ times greater than observed. Very different model performance was seen at the 600 km arc
of receptors with simulated maximum and CWIC that were 2 to 2 ½ times lower than observed
and lateral dispersion that was 2½ to 3½ times greater than observed.
2.3.4 ETEX and ATMES‐II
After the Chernobyl accident in April 1986, the Atmospheric Transport Model Evaluation Study
(ATMES) was initiated to compare the evolution of the radioactive cloud from Chernobyl with
predictions by mathematical models for atmospheric dispersion, using as input the estimated
source term and the meteorological data for the days following the accident. Considerable
work was undertaken by ATMES in order to identify and make available the databases of
radionuclide concentration in air measured after the Chernobyl accident and of meteorological
conditions that occurred. The ATMES LRT dispersion modeling and model evaluation was
conducted in the 1989‐1990 time period. The performance of the LRT models to predict the
observed radionuclides was hampered by the poor characterization of the emissions release
from Chernobyl.
In May 1989, it was proposed to carry out a massive tracer experiment in Europe designed to
address the weaknesses of ATMES modeling. In the following year the proposal was analyzed
and modified to adapt it to the European context, and to take account of the ATMES results, as
they became available. The experiment was named ETEX 16 , European Tracer Experiment. It
was designed to test the readiness of interested services to respond in the case of an
emergency, to organize the tracer release and compile a data set of measured air
concentrations and to investigate the performance of long range atmospheric transport and
dispersion models using that data set.
The period 15 October‐15 December 1994 was selected as the possible window for the two
tracer experiments as part of ETEX. The first release started at 1600 UTC on October 23, 1994,
and lasted 11 hours and 50 minutes. 340 kg of PMCH (perfluoromethylcyclohexane) tracer were
released in Monterfil, France (48° 03’ 30’’ N, 2° 00’ 30’’ W) at an average flow rate of 8.0 g/s.
The second ETEX tracer experiment started at 1500 UTC on November 14, 1994 and lasted for 9
hours and 45 minutes and released 490 kg of PMCP (perfluromethlcyclopentane) from
Monterfil for an average release rate of 11.58 g/s.
16 http://rem.jrc.ec.europa.eu/etex/
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