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

36 kilometers and the vertical structure contained 43 vertical layers. Physics options were not
optimized for northern European operations, but were based upon more advanced physics
options available in MM5, reflecting the findings of Deng et al. (2004). Key MM5 options
included:
• ETA Planetary Boundary Layer (PBL) scheme;
• Kain‐Fritsch II cumulus parameterization (Kain, 2004);
• Rapid Radiative Transfer Model (RRTM) radiation scheme (Mlawer et al. 1997);
• NOAH land surface model (LSM) (Chen et al. 2001); and
• Dudhia Simple Ice microphysics scheme (Dudhia, 1989).
Four dimensional data assimilation (FDDA) (Stauffer et al. 1990, 1991) was employed for this
study. “Analysis nudging” based upon the NCEP reanalysis fields were used with default values
for nudging strengths.
6.2.3 LRT Model Configuration and Inputs
Three distinct classes of LRT dispersion models were included as part of the ETEX tracer
evaluation including four Lagrangian models and one Eulerian model. CALPUFF Version 5.8
(Scire et al. 2000b) and SCIPUFF Version 2.303 (Sykes et al., 1998) are Lagrangian Gaussian puff
models. HYSPLIT Version 4.8 (Draxler 1997) and FLEXPART Version 6.2 (Siebert 2006) are
Lagrangian particle models. CAMx Version 5.2 (ENVIRON, 2010) is an Eulerian grid model. The
respective user’s guides provide a complete description of the technical formulations of each of
these models.
Both CALPUFF and SCIPUFF are based upon Gaussian puff formulation. The two puff models
have the advantage of more robust capabilities for source characterization, having the ability to
treat dispersion for point, area, or line sources. Furthermore, these models can more
accurately characterize dynamic releases of pollutants by accounting for initial plume rise of the
pollutant. Conversely, the two particle models are very limited in their capability to
characterize sources, having no direct ability to account for variations in source configurations
or consider plume rise. The CAMx grid model is limited in its ability to simulate “plumes” by the
grid resolution specified. CAMx includes a subgrid‐scale Plume‐in‐Grid (PiG) module to treat
the early evolution, transport and dispersion of point source plumes whose effect on model
performance was investigated using sensitivity tests.
Since plume rise varies from hour‐to‐hour as a function of ambient temperature, wind speed
and stability it is not possible to define a release height which would reflect this variation.
Therefore, a constant release height of 10 meters was assigned for the two particle models in
this study. This limitation of the particle models is problematic when comparing against models
such as CALPUFF, SCIPUFF and CAMx that can simulate dynamic releases of emissions and
calculate hour‐specific plume rise using hourly meteorological data. Iwasaki et al. (1998) found
that the initial release height assigned to the Japan Meteorological Agency (JMA) particle model
had a large impact on the predicted ground level concentrations. Investigation of initial release
height sensitivity of the two particle models was beyond the scope of this evaluation. However,
this limitation should be noted when considering the uncertainty of concentration estimates
from the two particle models.
Each of the four models requires gridded meteorological fields for dispersion calculations.
CALPUFF normally uses output from the CALMET diagnostic wind field model (Scire et al.,
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