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

1.0 INTRODUCTION
Dispersion models, such as the Industrial Source Complex Short Term (ISCST; EPA, 1995) or
American Meteorological Society/Environmental Protection Agency Regulatory Model
(AERMOD; EPA, 2004; 2009c) typically assume steady‐state, horizontally homogeneous wind
fields instantaneously over the entire modeling domain and are usually limited to distances of
less than 50 kilometers from a source. However, dispersion model applications of distances of
hundreds of kilometers from a source require other models or modeling systems. At these
distances, the transport times are sufficiently long that the mean wind fields cannot be
considered steady‐state or homogeneous. As part of the Prevention of Significant
Deterioration (PSD) program, new sources or proposed modifications to existing sources may
be required to assess the air quality and Air Quality Related Values (AQRVs) impacts at Class I
and sensitive Class II areas that may be far away from the source. AQRVs include visibility and
acid (sulfur and nitrogen) deposition. There are 156 federally mandated Class I areas in the
U.S. that consist of National Parks, Wilderness Areas and Wildlife Refuges that are administered
by Federal Land Managers (FLMs) from the National Park Service (NPS), United States Forest
Service (USFS) and Fish and Wildlife Service (FWS), respectively. Thus, non‐steady‐state Long
Range Transport (LRT) dispersion models are needed to address air quality and AQRVs issues at
distances beyond 50 km from a source.
1.1 BACKGROUND
The Interagency Workgroup on Air Quality Modeling (IWAQM) was formed to provide a focus
for the development of technically sound recommendations regarding assessment of air
pollutant source impacts on Federal Class I areas. Meetings were held with personnel from
interested Federal agencies, including the Environmental Protection Agency (EPA), the USFS,
NPS and FWS. The purpose of these meetings was to review respective modeling programs, to
develop an organizational framework, and to formulate reasonable objectives and plans that
could be presented to management for support and commitment. One objective of the
IWAQM is the recommendation of LRT dispersion models for assessing air quality and AQRVs at
Class I areas.
One such LRT dispersion model is the CALPUFF modeling system (Scire et al., 2000b). The
CALPUFF modeling system consists of several components: (1) CALMET (Scire et al., 2000a), a
meteorological preprocessor that can use as input surface, upper air, and/or on‐site
meteorological observations and/or prognostic meteorological model output data to create a
three‐dimensional wind field and derive boundary layer parameters based on gridded land use
data; (2) CALPUFF, a Lagrangian puff dispersion model that can simulate the effects of
temporally and spatially varying meteorological conditions on pollutant transport, remove
pollutants through dry and wet deposition processes, and includes limited ability to transform
pollutant species through chemical reactions; and (3) CALPOST, a postprocessor that takes the
hourly estimates from CALPUFF and generates n‐hr estimates as well as tables of maximum
values.
In 1998, EPA published the report entitled “A Comparison of CALPUFF Modeling Results to Two
Tracer Field Experiments” (EPA‐454/R‐98‐009) (EPA, 1998a). The 1998 EPA study examined
concentration estimates from the CALPUFF dispersion model that were compared to observed
tracer concentrations from two short term field experiments. The first experiment was at the
Savannah River Laboratory (SRL75) in South Carolina in December 1975 (DOE, 1978) and the
second was the Great Plains experiment (GP80) near Norman, Oklahoma (Ferber et al., 1981) in
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