Table of Contents - The Atmospheric Studies Group at TRC
Table of Contents - The Atmospheric Studies Group at TRC Table of Contents - The Atmospheric Studies Group at TRC
Section 1: Introduction on the puffs generated from the original puff, which under some conditions can substantially increase the effective rate of horizontal growth of the plume. Building Downwash: The Huber-Snyder and Schulman-Scire downwash models are both incorporated into CALPUFF. An option is provided to use either model for all stacks, or make the choice on a stackby-stack and wind sector-by-wind sector basis. Both algorithms have been implemented in such a way as to allow the use of wind direction specific building dimensions. The more advanced treatment of the PRIME downwash model is also incorporated as an option. This includes treating representative streamline patterns and diffusion rates in both the near and far wakes and recirculation effects in the cavity zone. Overwater and Coastal Interaction Effects: Because the CALMET meteorological model contains both overwater and overland boundary layer algorithms, the effects of water bodies on plume transport, dispersion, and deposition can be simulated with CALPUFF. The puff formulation of CALPUFF is designed to handle spatial changes in meteorological and dispersion conditions, including the abrupt changes that occur at the coastline of a major body of water. A subgrid TIBL option is also provided to better resolve the relationship between the coastline and source locations during periods conducive to onshore fumigation events. Dispersion Coefficients: Several options are provided in CALPUFF for the computation of dispersion coefficients, including the use of turbulence measurements (σ v and σ w ), the use of similarity theory to estimate σ v and σ w from modeled surface heat and momentum fluxes, or the use of Pasquill-Gifford (PG) or McElroy-Pooler (MP) dispersion coefficients, or dispersion equations based on the Complex Terrain Dispersion Model (CDTM). Options are provided to apply an averaging time correction or surface roughness length adjustments to the PG coefficients. When similarity theory is used to compute turbulence-based dispersion coefficients, an option is also provided for a PDF treatment of dispersion in the convective boundary layer. 1-25
Section 1: Introduction Table 1-2: Major Features of the CALPUFF Model • Source types Point sources (constant or variable emissions) Line sources (constant or variable emissions) Volume sources (constant or variable emissions) Area sources (constant or variable emissions) • Non-steady-state emissions and meteorological conditions Gridded 3-D fields of meteorological variables (winds, temperature) Spatially-variable fields of mixing height, friction velocity, convective velocity scale, Monin-Obukhov length, precipitation rate Vertically and horizontally-varying turbulence and dispersion rates Time-dependent source and emissions data • Efficient sampling functions Integrated puff formulation Elongated puff (slug) formulation • Dispersion coefficient (σ y , σ z ) options Direct measurements of σ v and σ w Estimated values of σ v and σ w based on similarity theory PDF treatment of dispersion in convective boundary layers Pasquill-Gifford (PG) dispersion coefficients (rural areas) McElroy-Pooler (MP) dispersion coefficients (urban areas) CTDM dispersion coefficients (neutral/stable) • Vertical wind shear Puff splitting Differential advection and dispersion • Plume rise Partial penetration Buoyant and momentum rise Stack tip effects Vertical wind shear Building downwash effects • Building downwash Huber-Snyder method Schulman-Scire method PRIME method (Continued) 1-26
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Section 1: Introduction<br />
on the puffs gener<strong>at</strong>ed from the original puff, which under some conditions can substantially increase the<br />
effective r<strong>at</strong>e <strong>of</strong> horizontal growth <strong>of</strong> the plume.<br />
Building Downwash: <strong>The</strong> Huber-Snyder and Schulman-Scire downwash models are both incorpor<strong>at</strong>ed<br />
into CALPUFF. An option is provided to use either model for all stacks, or make the choice on a stackby-stack<br />
and wind sector-by-wind sector basis. Both algorithms have been implemented in such a way as<br />
to allow the use <strong>of</strong> wind direction specific building dimensions. <strong>The</strong> more advanced tre<strong>at</strong>ment <strong>of</strong> the<br />
PRIME downwash model is also incorpor<strong>at</strong>ed as an option. This includes tre<strong>at</strong>ing represent<strong>at</strong>ive<br />
streamline p<strong>at</strong>terns and diffusion r<strong>at</strong>es in both the near and far wakes and recircul<strong>at</strong>ion effects in the<br />
cavity zone.<br />
Overw<strong>at</strong>er and Coastal Interaction Effects: Because the CALMET meteorological model contains<br />
both overw<strong>at</strong>er and overland boundary layer algorithms, the effects <strong>of</strong> w<strong>at</strong>er bodies on plume transport,<br />
dispersion, and deposition can be simul<strong>at</strong>ed with CALPUFF. <strong>The</strong> puff formul<strong>at</strong>ion <strong>of</strong> CALPUFF is<br />
designed to handle sp<strong>at</strong>ial changes in meteorological and dispersion conditions, including the abrupt<br />
changes th<strong>at</strong> occur <strong>at</strong> the coastline <strong>of</strong> a major body <strong>of</strong> w<strong>at</strong>er. A subgrid TIBL option is also provided to<br />
better resolve the rel<strong>at</strong>ionship between the coastline and source loc<strong>at</strong>ions during periods conducive to<br />
onshore fumig<strong>at</strong>ion events.<br />
Dispersion Coefficients: Several options are provided in CALPUFF for the comput<strong>at</strong>ion <strong>of</strong> dispersion<br />
coefficients, including the use <strong>of</strong> turbulence measurements (σ v and σ w ), the use <strong>of</strong> similarity theory to<br />
estim<strong>at</strong>e σ v and σ w from modeled surface he<strong>at</strong> and momentum fluxes, or the use <strong>of</strong> Pasquill-Gifford (PG)<br />
or McElroy-Pooler (MP) dispersion coefficients, or dispersion equ<strong>at</strong>ions based on the Complex Terrain<br />
Dispersion Model (CDTM). Options are provided to apply an averaging time correction or surface<br />
roughness length adjustments to the PG coefficients. When similarity theory is used to compute<br />
turbulence-based dispersion coefficients, an option is also provided for a PDF tre<strong>at</strong>ment <strong>of</strong> dispersion in<br />
the convective boundary layer.<br />
1-25
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