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

puffs expand until they exceed the size of the meteorological grid cell (either horizontally
or vertically) and then split into several new puffs, each with its share of the pollutant
mass. In the particle model, a fixed number of particles are advected about the model
domain by the mean wind field and spread by a turbulent component. The model's default
configuration assumes a 3‐dimensional particle distribution (horizontal and vertical).
FLEXPART 12 : The FLEXPART (Version 6.2; Siebert, 2006; Stohl et al., 2005 13 ) model is a
Lagrangian particle dispersion model developed at the Norwegian Institute for Air
Research in the Department of Atmospheric and Climate Research. FLEXPART was
originally designed for calculating the long‐range and mesoscale dispersion of air
pollutants from point sources, such as after an accident in a nuclear power plant. In the
meantime FLEXPART has evolved into a comprehensive tool for atmospheric transport
modeling and analysis
CAMx 14 : The Comprehensive Air‐quality Model with extensions (CAMx; ENVIRON, 2010) is
a photochemical grid model (PGM) that simulates inert or chemical reactive pollutants
from the local to continental scale. As a grid model, it simulates transport and dispersion
using finite difference techniques on a three‐dimensional array of grid cells. To treat the
near‐source dispersion of plumes, CAMx includes a subgrid‐scale Lagrangian puff Plume‐
in‐Grid (PiG) module whose mass is transferred to the grid model when the plume size is
comparable to the grid size.
CALGRID: The California Mesoscale Photochemical Grid Model (Yamartino, et al., 1989,
Scire et al., 1989; Earth Tech, 2005) is a PGM that simulates chemically reactive pollutants
from the local to regional scale. As with CAMx, it is a grid model that simulates transport
and dispersion using finite differencing techniques on a three‐dimensional array of grid
cells. CALGRID was originally designed to utilize meteorological fields produced by the
CALMET meteorological processor (Scire et al., 2000a), but was updated in 2006 to utilize
meteorology and emissions in UAM format (Earth Tech, 2006).
Although up to six LRT dispersion models were run for two of the tracer field experiments, a key
component of this study was the evaluation of the CALPUFF model and running CALPUFF with
various configurations of its meteorological drivers, CALMET and MMIF to help inform
regulatory guidance on the operation of the CALPUFF system. Key to developing insight into
the performance of any single model is to evaluate other models when configured similarly and
using similar meteorological databases. Table 2‐1 summarizes which LRT models were run with
the four field study tracer experiments presented in this report.
For the GP80 CALPUFF/CALMET application, numerous CALPUFF sensitivity tests were
performed using different configurations of CALMET including with and without MM5 data and
use of no observations. A limited set of CALPUFF sensitivity tests were also conducted using
different dispersion options. The other LRT models (save CALGRID) results were also evaluated
for the 600 km distant arc of receptors, but are not presented in the CALPUFF comparison
because this evaluation is based upon the NOAA DATEM statistical framework and is not
consistent with how CALPUFF was evaluated by EPA for this experiment in 1998.
12 http://transport.nilu.no/flexpart
13 http://www.atmos‐chem‐phys.net/5/2461/2005/acp‐5‐2461‐2005.html
14 http://www.camx.com/
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