Table of Contents - The Atmospheric Studies Group at TRC

Section 1: Introduction
released a Phase I report (EPA, 1993) which recommended using the MESOPUFF II dispersion model
and MESOPAC II meteorological model on an interim basis for simulating regional air quality and
visibility impacts. These recommendations were to apply until more refined (Phase 2) techniques could
be identified and evaluated. As part of the development of the Phase 2 recommendations, IWAQM
reviewed and intercompared diagnostic wind field models, tested the use of coarse gridded wind fields
from the Penn State/NCAR Mesoscale Model with four dimensional data assimilation (MM4) as input
into the diagnostic models, and evaluated the MESOPUFF II and CALPUFF modeling systems using
tracer data collected during the Cross-Appalachian Tracer Experiment (CAPTEX). The CAPTEX
evaluation results (EPA, 1995) indicated that by using the CALMET/ CALPUFF models with MM4 data,
performance could be improved over that obtained with the interim Phase I modeling approach. The
Phase 2 IWAQM report (EPA, 1998) recommends the use of the CALMET and CALPUFF models for
estimating air quality impacts relative to the National Ambient Air Quality Standards (NAAQS) and
Prevention of Significant Deterioration (PSD) increments.
The CALMET and CALPUFF models have been substantially revised and enhanced as part of work for
IWAQM, U.S. EPA, the USDA Forest Service, the US Department of the Interior Minerals Management
Service (MMS), the Environmental Protection Authority of Victoria (Australia), and private industry in
the U.S. and abroad. The improvements to CALMET included modifications to make it more suitable for
regional applications such as the use of a spatially variable initial guess field, an option for using hourly
MM4 or MM5 gridded fields as a supplement to observational data, the ability to compute Lambert
conformal map factors, a modified mixing height scheme, an option to use similarity theory to vertically
extrapolate surface wind observations, an enhanced algorithm to compute the three-dimensional
temperature fields over water bodies, improved initialization techniques, a refined slope flow
parameterization, and an optional PC-based Graphical User Interface (GUI) to facilitate model setup and
execution and to provide access to on-line Help files. Improvements to CALPUFF include new modules
to treat buoyant rise and dispersion from area sources (such as forest fires), buoyant line sources, volume
sources, an improved treatment of complex terrain, additional model switches to facilitate its use in
regulatory applications, enhanced treatment of wind shear through puff splitting, use of a probability
density function (pdf) to describe dispersion during convective conditions, and an optional GUI.
CALPUFF has been coupled to the Emissions Production Model (EPM) developed by the Forest Service
through an interface processor. EPM provides time-dependent emissions and heat release data for use in
modeling controlled burns and wildfires.
The most recent update of the system was prepared for the MMS in late 2005 as part of a multi-year study
to develop an updated regulatory model for evaluating air quality impacts from emission sources located
on federal waters of the Outer Continental Shelf (OCS). Its focus was to modify and/or enhance an
existing model so that it can be appropriately applied to overwater transport and dispersion simulations
using the most current knowledge, and is versatile enough to be used in short-range as well as long-range
regulatory applications. Changes to the system that were designed and implemented for OCS applications
include ease-of-use features as well as new and modified subroutines in both the CALMET
meteorological model and the CALPUFF dispersion model:
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