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

The evaluation of the LRT models using the SRL75 tracer data only has results for CALPUFF.
Several CALPUFF/CALMET sensitivity tests were run using only meteorological observations,
only MM5 data and hybrid MM5 plus meteorological observations. CALPUFF/MMIF was run
using 36, 12 and 4 km MM5 data.
Two tracer releases were evaluated using the CAPTEX database, Releases No. 3 and 5. While all
of the models listed in Table 2‐1 were run for the CAPTEX database, numerous CALMET
sensitivity tests were also conducted, including the evaluation of CALMET using various
configurations for CAPTEX Release No. 3 and 5 that helped define the EPA‐FLM recommended
CALMET settings in the August 2009 Clarification Memorandum (EPA, 2009b).
The LRT model intercomparison using the CAPTEX and ETEX databases was done differently
than the other two tracer test evaluations. The objective of the ETEX with CAPTEX LRT model
evaluation intercomparison was to evaluate the LRT dispersion models using a common
meteorological input database. Thus, all LRT models used the same MM5 meteorological
inputs.
Table 2‐1. Model availability for the four tracer test field experiments.
Model GP80 SRL75 CAPTEX ETEX
CALPUFF/CALMET Yes Yes Yes No
CALMET/MMIF Yes Yes Yes Yes
SCIPUFF No No Yes Yes
HYSPLIT No No Yes Yes
FLEXPART No No Yes Yes
CAMx No No Yes Yes
CALGRID No No Yes No
2.3 RELEATED PREVIOUS STUDIES
Over the years there have been numerous studies that have evaluated dispersion models using
tracer test and other field study databases. In fact, much of the early development of Gaussian
plume dispersion formulation was assisted by radioactive ambient field data (Slade, 1968). The
development and evaluation of the AERMOD steady‐state Gaussian plume model used almost
20 near‐source field study datasets 15 . The discussion below is limited to long range transport
(LRT) dispersion model evaluations that have been related to the development of the CALPUFF
modeling system, which in 2003 was identified as the EPA recommended regulatory LRT model
for far‐field (> 50 km) air quality modeling of chemically inert compounds (EPA, 2003).
2.3.1 1986 Evaluation of Eight Short‐Term Long Range Transport Models
EPA sponsored a study to evaluate 8 LRT models using the GP80 tracer field experiment and
Krypton‐85 releases from the Savannah River Laboratory (SRL; Telegadas et al., 1980) databases
(Policastro et al., 1986). The eight models were MESOPUFF, MESOPLUME, MSPUFF,
MESOPUFF‐II, MTDDIS, ARRPA, RADM and RTM‐II. MESOPUFF, MSPUFF and MESOPUFF‐II are
Lagrangian puff models that all have their original basis on the MESOPUFF model. MESOPLUME
is a Lagrangian plume segment model. MTDDIS is a variable trajectory model that also uses the
Gaussian puff formulation. ARRPA is a single‐source segmented plume model. RADM and
RTM‐II are Eulerian grid models. Model performance was evaluated by graphical and statistical
methods. The primary means for the evaluation of model performance was the use of the
American Meteorological Society (AMS) statistics (Fox, 1981). The AMS statistics recommends
15 http://www.epa.gov/ttn/scram/dispersion_prefrec.htm#aermod
7