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MACCS2 models atmospheric dispersion and transport, and includes models for deposition, weathering, resuspension, and radioactive decay. A Gaussian plume model is used to model plume dispersion during downwind transport. Scaling factors are used in MACCS2 to model effects of surface roughness on plume dispersion. Statistical distributions of consequence measures that depict the range and probability of consequences are generated by MACCS2 in terms of complementary cumulative distribution functions (CCDFs).[4] These distributions are generated using stratified Monte Carlo sampling of combinations of representative sets of source terms, weather sequences, and exposed populations. Radioactive decay and ingrowth, and dry and wet aerosol deposition processes are modeled. Economic effects models in MACCS2 are intended to estimate the direct offsite costs resulting from a reactor accident and include costs resulting from both short-term and long-term protective actions [3].
MACCS2 models atmospheric dispersion and transport, and includes models for deposition, weathering, resuspension, and radioactive decay. A Gaussian plume model is used to model plume dispersion during downwind transport. Scaling factors are used in MACCS2 to model effects of surface roughness on plume dispersion. Statistical distributions of consequence measures that depict the range and probability of consequences are generated by MACCS2 in terms of complementary cumulative distribution functions (CCDFs).[4] These distributions are generated using stratified Monte Carlo sampling of combinations of representative sets of source terms, weather sequences, and exposed populations. Radioactive decay and ingrowth, and dry and wet aerosol deposition processes are modeled. Economic effects models in MACCS2 are intended to estimate the direct offsite costs resulting from a reactor accident and include costs resulting from both short-term and long-term protective actions [3].
The principal phenomena considered in MACCS2 are atmospheric transport using a Gaussian plume model, short-term and long-term dose accumulation through several pathways (including cloudshine, groundshine, inhalation, deposition onto the skin, and food and water ingestion), mitigative actions based on dose projection, early and latent health effects, and economic costs. The following phenomena can be incorporated within a single calculation:
The principal phenomena considered in MACCS2 are atmospheric transport using a Gaussian plume model, short-term and long-term dose accumulation through several pathways (including cloudshine, groundshine, inhalation, deposition onto the skin, and food and water ingestion), mitigative actions based on dose projection, early and latent health effects, and economic costs. The following phenomena can be incorporated within a single calculation:
Release characteristics;
Release characteristics; Meteorological sampling; Atmospheric dispersion and deposition; Exposure pathways and duration; Protective actions and dose mitigation; Movement of populations as cohorts; Individual and population doses; and Health and economic consequences.
 
Meteorological sampling; Atmospheric dispersion and deposition; Exposure pathways and duration; Protective actions and dose mitigation; Movement of populations as cohorts; Individual and population doses; and Health and economic consequences.
MACCS2 has three major components, ATMOS, EARLY, and CHRONC. Of these components, only ATMOS, which treats dispersion and deposition using a Gaussian plume model, has similarities to AERMOD and CALPUFF. The EARLY and CHRONC modules are used to model emergency phase events and radiological consequences and economic costs of response actions, which are not considered in the functionality of AERMOD and CALPUFF.
MACCS2 has three major components, ATMOS, EARLY, and CHRONC. Of these components, only ATMOS, which treats dispersion and deposition using a Gaussian plume model, has similarities to AERMOD and CALPUFF. The EARLY and CHRONC modules are used to model emergency phase events and radiological consequences and economic costs of response actions, which are not considered in the functionality of AERMOD and CALPUFF.
ATMOS calculates the dispersion and deposition of material released to the atmosphere as a function of downwind distance, and uses a Gaussian plume model with Pasquill-Gifford dispersion parameters. ATMOS treats the following phenomena:
ATMOS calculates the dispersion and deposition of material released to the atmosphere as a function of downwind distance, and uses a Gaussian plume model with Pasquill-Gifford dispersion parameters. ATMOS treats the following phenomena:
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EPA Regulatory Atmospheric Modeling Codes Two code systems recommended by the U.S. Environmental Protection Agency (EPA) for use in regulatory atmospheric modeling, and required for use for several programs are the AERMOD and CALPUFF modeling systems [1,2]. The EPA Support Center for Regulatory Atmospheric Modeling website provides the following basic descriptions of these modeling systems [1]:
EPA Regulatory Atmospheric Modeling Codes Two code systems recommended by the U.S. Environmental Protection Agency (EPA) for use in regulatory atmospheric modeling, and required for use for several programs are the AERMOD and CALPUFF modeling systems [1,2]. The EPA Support Center for Regulatory Atmospheric Modeling website provides the following basic descriptions of these modeling systems [1]:
AERMOD Modeling System - A steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain.
AERMOD Modeling System - A steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain.
CALPUFF Modeling System - A non-steady-state puff dispersion model that simulates the effects of time- and space-varying meteorological conditions on pollution transport, transformation, and removal. CALPUFF can be applied for long-range transport and for complex terrain.
CALPUFF Modeling System - A non-steady-state puff dispersion model that simulates the effects of time- and space-varying meteorological conditions on pollution transport, transformation, and removal. CALPUFF can be applied for long-range transport and for complex terrain.
AERMOD Overview AERMOD was designed for short range (up to 50 km) dispersion from stationary sources, and includes modeling of surface terrain on the behavior of air pollution plumes and of building downwash effects. A Gaussian plume model is used [5]. AERMOD can model exponential decay. (The default regulatory option forces use of a 4 hr half life for SO2 in an urban source, and does not allow for exponential decay for other applications
AERMOD Overview AERMOD was designed for short range (up to 50 km) dispersion from stationary sources, and includes modeling of surface terrain on the behavior of air pollution plumes and of building downwash effects. A Gaussian plume model is used [5]. AERMOD can model exponential decay. (The default regulatory option forces use of a 4 hr half life for SO2 in an urban source, and does not allow for exponential decay for other applications
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evacuation), or economic models are included in CALPUFF.
evacuation), or economic models are included in CALPUFF.
A summary comparison of the dispersion and deposition models of the ATMOS component of MACCS2, AERMOD, and CALPUFF are shown in Table 1. More detailed summary information on the latter two codes from Appendix A to Appendix W of 40 CFR Part 51 is shown in Appendix A.
A summary comparison of the dispersion and deposition models of the ATMOS component of MACCS2, AERMOD, and CALPUFF are shown in Table 1. More detailed summary information on the latter two codes from Appendix A to Appendix W of 40 CFR Part 51 is shown in Appendix A.
 
Table 1. Summary Comparison of Atmospheric Dispersion and Deposition Models Parameter            MACCS2/ATMOS                  AERMOD                  CALPUFF Plume Model        Non-steady-state        Steady-state Gaussian  Non-steady-state Gaussian plume with      plume model            Lagrangian Gaussian multiple plume                                  puff model; segments;                                        Wind shear puff split; Plume expansion                                  Briggs model; factor for meander;                              Partial penetration; Briggs model for                                Buoyant and buoyant plume rise                              momentum rise; Stack tip effects; Vertical wind shear Dispersion          Two models:              No user input          Five models, Pasquill-Gifford                                including P-G stability class sigma-y and sigma-z; Time-based dispersion function Building Wake and  Building wake            Stack-tip downwash;    Building downwash Terrain Effects    entrainment;            Surface terrain effects by two methods; Surface terrain effects  (via surface roughness  Applicable to rough or modeled with scaling    length)                complex terrain; factor                                          Simulates changes in the flow and dispersion rate induced by terrain features Wet Deposition      Exponential function    Wet particulate and    Empirical scavenging of rain duration and    gaseous deposition      model as function of intensity                                        pollutant and precipitation type Dry Deposition      Source depletion by      Dry particulate and    Resistance model particle size            gaseous deposition dependent deposition velocity Meteorological      Weather bin or          Surface boundary        Hourly wind/temp on Sampling            random sampling of      layer and profile      3D grid, w/2D annual data;            variables;              parameters Specification of        Hourly time periods mixing layer height; 15-min, 30-min, or hourly time periods Material Sources    Point or area source    Multiple sources;      Time varying point, w/multiple plume        point, volume, area,    line, volume, and area segments, aerosol        and line;              sources; sizes, and isotopic      Variable emission      Variable emission components              rates                  rates Parameter                MACCS2/ATMOS                AERMOD                CALPUFF Receptor Locations      Polar grid centered on  Multiple receptors;    Essentially unlimited facility;              Discrete, polar or    gridded or discrete Up to 35 radial        Cartesian grid        receptors intervals;              networks; Up to 64 compass        Variable receptor directions;            height Up to 7 receptors per grid Range                  0.05 to 9999 km;        Up to 50 km            10s of m to 100s of km Decay and Ingrowth      Radioactive decay and  Single exponential    Linear removal and daughter ingrowth      decay                  chemical conversion over six generations All three codes use a type of Gaussian dispersion model. AERMOD uses the simplest Gaussian representation, which is a steady-state plume; MACCS2 also uses a plume model, but the wind speed, stability class, and precipitation rate can change as the plume moves through the grid. CALPUFF uses a Gaussian puff model, which allows wind direction to change along the course of the plume.
Table 1. Summary Comparison of Atmospheric Dispersion and Deposition Models Parameter            MACCS2/ATMOS                  AERMOD                  CALPUFF Plume Model        Non-steady-state        Steady-state Gaussian  Non-steady-state Gaussian plume with      plume model            Lagrangian Gaussian multiple plume                                  puff model; segments;                                        Wind shear puff split; Plume expansion                                  Briggs model; factor for meander;                              Partial penetration; Briggs model for                                Buoyant and buoyant plume rise                              momentum rise; Stack tip effects; Vertical wind shear Dispersion          Two models:              No user input          Five models, Pasquill-Gifford                                including P-G stability class sigma-y and sigma-z; Time-based dispersion function Building Wake and  Building wake            Stack-tip downwash;    Building downwash Terrain Effects    entrainment;            Surface terrain effects by two methods; Surface terrain effects  (via surface roughness  Applicable to rough or modeled with scaling    length)                complex terrain; factor                                          Simulates changes in the flow and dispersion rate induced by terrain features Wet Deposition      Exponential function    Wet particulate and    Empirical scavenging of rain duration and    gaseous deposition      model as function of intensity                                        pollutant and precipitation type Dry Deposition      Source depletion by      Dry particulate and    Resistance model particle size            gaseous deposition dependent deposition velocity Meteorological      Weather bin or          Surface boundary        Hourly wind/temp on Sampling            random sampling of      layer and profile      3D grid, w/2D annual data;            variables;              parameters Specification of        Hourly time periods mixing layer height; 15-min, 30-min, or hourly time periods Material Sources    Point or area source    Multiple sources;      Time varying point, w/multiple plume        point, volume, area,    line, volume, and area segments, aerosol        and line;              sources; sizes, and isotopic      Variable emission      Variable emission components              rates                  rates
 
Parameter                MACCS2/ATMOS                AERMOD                CALPUFF Receptor Locations      Polar grid centered on  Multiple receptors;    Essentially unlimited facility;              Discrete, polar or    gridded or discrete Up to 35 radial        Cartesian grid        receptors intervals;              networks; Up to 64 compass        Variable receptor directions;            height Up to 7 receptors per grid Range                  0.05 to 9999 km;        Up to 50 km            10s of m to 100s of km Decay and Ingrowth      Radioactive decay and  Single exponential    Linear removal and daughter ingrowth      decay                  chemical conversion over six generations All three codes use a type of Gaussian dispersion model. AERMOD uses the simplest Gaussian representation, which is a steady-state plume; MACCS2 also uses a plume model, but the wind speed, stability class, and precipitation rate can change as the plume moves through the grid. CALPUFF uses a Gaussian puff model, which allows wind direction to change along the course of the plume.
An important distinction between these codes is that AERMOD and CALPUFF were specifically designed to treat chemical air pollutants. Because of this, they treat removal of the pollutants by chemical reaction but do not handle radioactive decay with daughter ingrowth. On the other hand, MACCS2 was specifically designed to treat radioactive air pollutants. It treats radioactive decay and daughter ingrowth for decay chains up to a length of six.
An important distinction between these codes is that AERMOD and CALPUFF were specifically designed to treat chemical air pollutants. Because of this, they treat removal of the pollutants by chemical reaction but do not handle radioactive decay with daughter ingrowth. On the other hand, MACCS2 was specifically designed to treat radioactive air pollutants. It treats radioactive decay and daughter ingrowth for decay chains up to a length of six.
An approach to addressing the objective of this plan is to evaluate whether or not output generated by AERMOD and CALPUFF could be used as input to a post-processing routine to model radioactive decay and dose pathway processes, emergency phase relocation actions, and economic costs. That is, AERMOD and CALPUFF account for plume dispersion and deposition, and provide material concentrations at receptor locations. Approximation would be needed to model radioactive decay with daughter ingrowth during atmospheric transport for a large set of parents and daughters, and the corresponding adjustment made to deposited concentrations. An approach to modeling cloudshine effects would also be needed to ensure that predictions are not underestimated. From the deposited material concentrations, it may be possible to develop a set of dose conversion factors to account for various uptake pathways. The most difficult implementation would be to account for the interaction between time-dependent plume concentrations and evacuating public.                  Deposited material concentrations could be used to estimate economic costs for mitigative actions.
An approach to addressing the objective of this plan is to evaluate whether or not output generated by AERMOD and CALPUFF could be used as input to a post-processing routine to model radioactive decay and dose pathway processes, emergency phase relocation actions, and economic costs. That is, AERMOD and CALPUFF account for plume dispersion and deposition, and provide material concentrations at receptor locations. Approximation would be needed to model radioactive decay with daughter ingrowth during atmospheric transport for a large set of parents and daughters, and the corresponding adjustment made to deposited concentrations. An approach to modeling cloudshine effects would also be needed to ensure that predictions are not underestimated. From the deposited material concentrations, it may be possible to develop a set of dose conversion factors to account for various uptake pathways. The most difficult implementation would be to account for the interaction between time-dependent plume concentrations and evacuating public.                  Deposited material concentrations could be used to estimate economic costs for mitigative actions.
However, the mitigative actions, such as decontamination of property, are coupled with public doses. As a result, a coupled model is required to properly treat these effects.
However, the mitigative actions, such as decontamination of property, are coupled with public doses. As a result, a coupled model is required to properly treat these effects.
Unlike MACCS2, neither AERMOD nor CALPUFF appear to have options for generating statistical distributions of consequences for variations in source terms, meteorology, or populations. Alternatively, it may be possible to incorporate these modeling functions in the codes directly.
Unlike MACCS2, neither AERMOD nor CALPUFF appear to have options for generating statistical distributions of consequences for variations in source terms, meteorology, or populations. Alternatively, it may be possible to incorporate these modeling functions in the codes directly.
Developing, testing, producing quality assurance (QA) documentation, and obtaining EPA approval for either AERMOD or CALPUFF in the context of nuclear reactor accidents would likely require considerable effort over a period of several years.
Developing, testing, producing quality assurance (QA) documentation, and obtaining EPA approval for either AERMOD or CALPUFF in the context of nuclear reactor accidents would likely require considerable effort over a period of several years.
Some of the steps involved are shown in the following graphic.
Some of the steps involved are shown in the following graphic.
AERMOD Output For each averaging period (1, 3, 8, or 24 hours or 1 month), concurrent averages for all receptors for each day of data processed are generated. Receptor networks are printed first, followed by concurrent averages for each source group. Optional output files include POSTFILE, a file of concurrent (raw) results at each receptor. Appendix D of the AERMOD User Guide shows for the POSTFILE option a file including X and Y coordinates of the receptor location, receptor height, averaging period, source group ID, and either the date variable for the end of the averaging period or the number of hours in the period for period averages [9].
AERMOD Output For each averaging period (1, 3, 8, or 24 hours or 1 month), concurrent averages for all receptors for each day of data processed are generated. Receptor networks are printed first, followed by concurrent averages for each source group. Optional output files include POSTFILE, a file of concurrent (raw) results at each receptor. Appendix D of the AERMOD User Guide shows for the POSTFILE option a file including X and Y coordinates of the receptor location, receptor height, averaging period, source group ID, and either the date variable for the end of the averaging period or the number of hours in the period for period averages [9].
CALPUFF Output CALPUFF output files include one-hour averaged concentrations at gridded and discrete receptor locations for selected species and of wet and dry deposition fluxes; hourly reports of mass fluxes into and out of regions, and of mass changes for all species, are also produced. The CALPOST postprocessor program averages and reports concentrations or wet/dry fluxes based on hourly data in the CALPUFF output file [12].
CALPUFF Output CALPUFF output files include one-hour averaged concentrations at gridded and discrete receptor locations for selected species and of wet and dry deposition fluxes; hourly reports of mass fluxes into and out of regions, and of mass changes for all species, are also produced. The CALPOST postprocessor program averages and reports concentrations or wet/dry fluxes based on hourly data in the CALPUFF output file [12].
Summary The objective of this plan is to determine the feasibility, and if appropriate, the level of effort required to use the AERMOD and CALPUFF models in the same capacity as MACCS2 for performing consequence modeling in terms of dose, health effects, land contamination, and economic cost for SAMA analyses. Because AERMOD and CALPUFF do not include models for emergency response, radioactive decay and ingrowth, radiological health effects, mitigative actions, or economic costs, code revision or development of post-processing utilities would be needed to utilize either of these codes to model nuclear reactor accident consequences in a manner similar to MACCS2.
Summary The objective of this plan is to determine the feasibility, and if appropriate, the level of effort required to use the AERMOD and CALPUFF models in the same capacity as MACCS2 for performing consequence modeling in terms of dose, health effects, land contamination, and economic cost for SAMA analyses. Because AERMOD and CALPUFF do not include models for emergency response, radioactive decay and ingrowth, radiological health effects, mitigative actions, or economic costs, code revision or development of post-processing utilities would be needed to utilize either of these codes to model nuclear reactor accident consequences in a manner similar to MACCS2.
Statistical sampling of parameter distributions is also a feature of MACCS2 that is not available in AERMOD or CALPUFF. Developing, testing, and acquiring acceptance of the results produced by these approaches would involve significant effort. Model assumptions and constraints needed for these utilities may limit the accuracy/fidelity of the results obtained.
Statistical sampling of parameter distributions is also a feature of MACCS2 that is not available in AERMOD or CALPUFF. Developing, testing, and acquiring acceptance of the results produced by these approaches would involve significant effort. Model assumptions and constraints needed for these utilities may limit the accuracy/fidelity of the results obtained.
References
References
: 1. Preferred/Recommended Models, Technology Transfer Network, Support Center for Regulatory Atmospheric Modeling, U.S. Environmental Protection Agency, http://www.epa.gov/scram001/dispersion_prefrec.htm, accessed May 6, 2010.
: 1. Preferred/Recommended Models, Technology Transfer Network, Support Center for Regulatory Atmospheric Modeling, U.S. Environmental Protection Agency, http://www.epa.gov/scram001/dispersion_prefrec.htm, accessed May 6, 2010.
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: 11. Question 1.1.1., CALPUFF FAQs Answers, CALPUFF Modeling, The Atmospheric Studies Group at TRC, http://www.src.com/calpuff/FAQ-answers.htm#1.1.1 , accessed 4/29/2010.
: 11. Question 1.1.1., CALPUFF FAQs Answers, CALPUFF Modeling, The Atmospheric Studies Group at TRC, http://www.src.com/calpuff/FAQ-answers.htm#1.1.1 , accessed 4/29/2010.
: 12. Scire, J.S. D.G. Strimaitis, and R.J. Yamartino, A Users Guide for the CALPUFF Dispersion Model (Version 5), Earth Tech, Inc., January 2000.
: 12. Scire, J.S. D.G. Strimaitis, and R.J. Yamartino, A Users Guide for the CALPUFF Dispersion Model (Version 5), Earth Tech, Inc., January 2000.
Appendix A. Key Features of Refined Air Quality Models Parameter                    AERMOD1                                    CALPUFF1 Type of Model  AERMOD is a steadystate plume model,    (1) CALPUFF is a nonsteadystate time using Gaussian distributions in the      and spacedependent Gaussian puff vertical and horizontal for stable        model. CALPUFF treats primary conditions, and in the horizontal for    pollutants and simulates secondary convective conditions. The vertical      pollutant formation using a concentration distribution for convective parameterized, quasilinear chemical conditions results from an assumed bi    conversion mechanism. Pollutants Gaussian probability density function of  treated include SO2, SO42, NOX (i.e., NO +
Appendix A. Key Features of Refined Air Quality Models Parameter                    AERMOD1                                    CALPUFF1 Type of Model  AERMOD is a steadystate plume model,    (1) CALPUFF is a nonsteadystate time using Gaussian distributions in the      and spacedependent Gaussian puff vertical and horizontal for stable        model. CALPUFF treats primary conditions, and in the horizontal for    pollutants and simulates secondary convective conditions. The vertical      pollutant formation using a concentration distribution for convective parameterized, quasilinear chemical conditions results from an assumed bi    conversion mechanism. Pollutants Gaussian probability density function of  treated include SO2, SO42, NOX (i.e., NO +
the vertical velocity.                    NO2), HNO3, NO3, NH3, PM-10, PM-2.5, toxic pollutants and others pollutant species that are either inert or subject to quasilinear chemical reactions. The model includes a resistancebased dry deposition model for both gaseous pollutants and particulate matter. Wet deposition is treated using a scavenging coefficient approach. The model has detailed parameterizations of complex terrain effects, including terrain impingement, sidewall scraping, and steepwalled terrain influences on lateral plume growth. A subgridscale complex terrain module based on a dividing streamline concept divides the flow into a lift component traveling over the obstacle and a wrap component deflected around the obstacle.
the vertical velocity.                    NO2), HNO3, NO3, NH3, PM-10, PM-2.5, toxic pollutants and others pollutant species that are either inert or subject to quasilinear chemical reactions. The model includes a resistancebased dry deposition model for both gaseous pollutants and particulate matter. Wet deposition is treated using a scavenging coefficient approach. The model has detailed parameterizations of complex terrain effects, including terrain impingement, sidewall scraping, and steepwalled terrain influences on lateral plume growth. A subgridscale complex terrain module based on a dividing streamline concept divides the flow into a lift component traveling over the obstacle and a wrap component deflected around the obstacle.
(2) The meteorological fields used by CALPUFF are produced by the CALMET meteorological model. CALMET includes a diagnostic wind field model containing parameterized treatments of slope flows, valley flows, terrain blocking effects, and kinematic terrain effects, lake and sea breeze circulations, a divergence minimization procedure, and objective analysis of observational data. An energybalance scheme is used to compute sensible and latent heat fluxes and turbulence parameters over land surfaces. A profile method is used over water. CALMET contains interfaces to prognostic meteorological models such as the Penn State/NCAR Mesoscale Model (e.g., MM5; Section 12.0, ref. 86),
(2) The meteorological fields used by CALPUFF are produced by the CALMET meteorological model. CALMET includes a diagnostic wind field model containing parameterized treatments of slope flows, valley flows, terrain blocking effects, and kinematic terrain effects, lake and sea breeze circulations, a divergence minimization procedure, and objective analysis of observational data. An energybalance scheme is used to compute sensible and latent heat fluxes and turbulence parameters over land surfaces. A profile method is used over water. CALMET contains interfaces to prognostic meteorological models such as the Penn State/NCAR Mesoscale Model (e.g., MM5; Section 12.0, ref. 86),
as well as the RAMS, Ruc and Eta models.
as well as the RAMS, Ruc and Eta models.
Parameter                    AERMOD1                                    CALPUFF1 Pollutant Types AERMOD is applicable to primary          CALPUFF may be used to model gaseous pollutants and continuous releases of    pollutants or particulate matter that are toxic and hazardous waste pollutants. inert or which undergo quasilinear Chemical transformation is treated by    chemical reactions, such as SO2, SO42, simple exponential decay.                NOX (i.e., NO + NO2), HNO3, NO3, NH3, PM-10, PM-2.5 and toxic pollutants. For regional haze analyses, sulfate and nitrate particulate components are explicitly treated.
Parameter                    AERMOD1                                    CALPUFF1 Pollutant Types AERMOD is applicable to primary          CALPUFF may be used to model gaseous pollutants and continuous releases of    pollutants or particulate matter that are toxic and hazardous waste pollutants. inert or which undergo quasilinear Chemical transformation is treated by    chemical reactions, such as SO2, SO42, simple exponential decay.                NOX (i.e., NO + NO2), HNO3, NO3, NH3, PM-10, PM-2.5 and toxic pollutants. For regional haze analyses, sulfate and nitrate particulate components are explicitly treated.
SourceReceptor AERMOD applies userspecified locations  CALPUFF contains no fundamental Relationships  for sources and receptors. Actual        limitations on the number of sources or separation between each source          receptors. Parameter files are provided receptor pair is used. Source and        that allow the user to specify the receptor elevations are user input or are maximum number of sources, determined by AERMAP using USGS DEM      receptors, puffs, species, grid cells, terrain data. Receptors may be located    vertical layers, and other model at userspecified heights above ground    parameters. Its algorithms are designed level.                                    to be suitable for sourcereceptor distances from tens of meters to hundreds of kilometers.
SourceReceptor AERMOD applies userspecified locations  CALPUFF contains no fundamental Relationships  for sources and receptors. Actual        limitations on the number of sources or separation between each source          receptors. Parameter files are provided receptor pair is used. Source and        that allow the user to specify the receptor elevations are user input or are maximum number of sources, determined by AERMAP using USGS DEM      receptors, puffs, species, grid cells, terrain data. Receptors may be located    vertical layers, and other model at userspecified heights above ground    parameters. Its algorithms are designed level.                                    to be suitable for sourcereceptor distances from tens of meters to hundreds of kilometers.
Parameter                    AERMOD1                                    CALPUFF1 Plume Behavior (1) In the convective boundary layer        Momentum and buoyant plume rise is (CBL), the transport and dispersion of a  treated according to the plume rise plume is characterized as the              equations of Briggs (1975) for non superposition of three modeled plumes:    downwashing point sources, Schulman The direct plume (from the stack), the    and Scire (1980) for line sources and indirect plume, and the penetrated        point sources subject to building plume, where the indirect plume            downwash effects using the Schulman accounts for the lofting of a buoyant      Scire downwash algorithm, and Zhang plume near the top of the boundary        (1993) for buoyant area sources and layer, and the penetrated plume            point sources affected by building accounts for the portion of a plume that,  downwash when using the PRIME due to its buoyancy, penetrates above      building downwash method. Stack tip the mixed layer, but can disperse          downwash effects and partial plume downward and reenter the mixed layer. penetration into elevated temperature In the CBL, plume rise is superposed on    inversions are included. An algorithm to the displacements by random convective    treat horizontallyoriented vents and velocities (Weil et al., 1997).            stacks with rain caps is included.
Parameter                    AERMOD1                                    CALPUFF1 Plume Behavior (1) In the convective boundary layer        Momentum and buoyant plume rise is (CBL), the transport and dispersion of a  treated according to the plume rise plume is characterized as the              equations of Briggs (1975) for non superposition of three modeled plumes:    downwashing point sources, Schulman The direct plume (from the stack), the    and Scire (1980) for line sources and indirect plume, and the penetrated        point sources subject to building plume, where the indirect plume            downwash effects using the Schulman accounts for the lofting of a buoyant      Scire downwash algorithm, and Zhang plume near the top of the boundary        (1993) for buoyant area sources and layer, and the penetrated plume            point sources affected by building accounts for the portion of a plume that,  downwash when using the PRIME due to its buoyancy, penetrates above      building downwash method. Stack tip the mixed layer, but can disperse          downwash effects and partial plume downward and reenter the mixed layer. penetration into elevated temperature In the CBL, plume rise is superposed on    inversions are included. An algorithm to the displacements by random convective    treat horizontallyoriented vents and velocities (Weil et al., 1997).            stacks with rain caps is included.
(2) In the stable boundary layer, plume rise is estimated using an iterative approach, similar to that in the CTDMPLUS model (see A.5 in this appendix).
(2) In the stable boundary layer, plume rise is estimated using an iterative approach, similar to that in the CTDMPLUS model (see A.5 in this appendix).
Line 106: Line 94:
(4) For elevated terrain, AERMOD incorporates the concept of the critical dividing streamline height, in which flow below this height remains horizontal, and flow above this height tends to rise up and over terrain (Snyder et al., 1985).
(4) For elevated terrain, AERMOD incorporates the concept of the critical dividing streamline height, in which flow below this height remains horizontal, and flow above this height tends to rise up and over terrain (Snyder et al., 1985).
Plume concentration estimates are the weighted sum of these two limiting plume states.
Plume concentration estimates are the weighted sum of these two limiting plume states.
Parameter                      AERMOD1                                    CALPUFF1 However, consistent with the steady state assumption of uniform horizontal wind direction over the modeling domain, straightline plume trajectories are assumed, with adjustment in the plume/receptor geometry used to account for the terrain effects.
Parameter                      AERMOD1                                    CALPUFF1 However, consistent with the steady state assumption of uniform horizontal wind direction over the modeling domain, straightline plume trajectories are assumed, with adjustment in the plume/receptor geometry used to account for the terrain effects.
Horizontal Winds Vertical profiles of wind are calculated    A threedimensional wind field is for each hour based on measurements        computed by the CALMET and surfacelayer similarity (scaling)      meteorological model. CALMET relationships. At a given height above      combines an objective analysis ground, for a given hour, winds are        procedure using wind observations with assumed constant over the modeling          parameterized treatments of slope flows, domain. The effect of the vertical          valley flows, terrain kinematic effects, variation in horizontal wind speed on      terrain blocking effects, and sea/lake dispersion is accounted for through        breeze circulations. CALPUFF may simple averaging over the plume depth.      optionally use single station (horizontallyconstant) wind fields in the CTDMPLUS, AERMOD or ISCST3 data formats.
Horizontal Winds Vertical profiles of wind are calculated    A threedimensional wind field is for each hour based on measurements        computed by the CALMET and surfacelayer similarity (scaling)      meteorological model. CALMET relationships. At a given height above      combines an objective analysis ground, for a given hour, winds are        procedure using wind observations with assumed constant over the modeling          parameterized treatments of slope flows, domain. The effect of the vertical          valley flows, terrain kinematic effects, variation in horizontal wind speed on      terrain blocking effects, and sea/lake dispersion is accounted for through        breeze circulations. CALPUFF may simple averaging over the plume depth.      optionally use single station (horizontallyconstant) wind fields in the CTDMPLUS, AERMOD or ISCST3 data formats.
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vertical profile of lateral turbulence      Initial plume size from area or volume between the plume height and the            sources is allowed.
vertical profile of lateral turbulence      Initial plume size from area or volume between the plume height and the            sources is allowed.
receptor height. The effective lateral turbulence is then used to estimate horizontal dispersion.
receptor height. The effective lateral turbulence is then used to estimate horizontal dispersion.
Parameter                          AERMOD1                                  CALPUFF1 Vertical            In the stable boundary layer, Gaussian        Turbulencebased dispersion Dispersion          vertical dispersion coefficients are      coefficients provide estimates of vertical estimated as continuous functions of      plume dispersion based on measured or parameterized vertical turbulence. In      computed values of w. The effects of the convective boundary layer, vertical    building downwash and buoyancy dispersion is characterized by a bi      induced dispersion are included. Vertical Gaussian probability density function,    dispersion during convective conditions and is also estimated as a continuous      is simulated with a probability density function of parameterized vertical        function (PDF) model based on Weil et turbulence. Vertical turbulence profiles  al. (1997). Options are provided to use are developed from measurements and        PasquillGifford (rural) and McElroy similarity (scaling) relationships. These  Pooler (urban) dispersion coefficients.
Parameter                          AERMOD1                                  CALPUFF1 Vertical            In the stable boundary layer, Gaussian        Turbulencebased dispersion Dispersion          vertical dispersion coefficients are      coefficients provide estimates of vertical estimated as continuous functions of      plume dispersion based on measured or parameterized vertical turbulence. In      computed values of w. The effects of the convective boundary layer, vertical    building downwash and buoyancy dispersion is characterized by a bi      induced dispersion are included. Vertical Gaussian probability density function,    dispersion during convective conditions and is also estimated as a continuous      is simulated with a probability density function of parameterized vertical        function (PDF) model based on Weil et turbulence. Vertical turbulence profiles  al. (1997). Options are provided to use are developed from measurements and        PasquillGifford (rural) and McElroy similarity (scaling) relationships. These  Pooler (urban) dispersion coefficients.
turbulence profiles account for both      Initial plume size from area or volume convective and mechanical turbulence.      sources is allowed.
turbulence profiles account for both      Initial plume size from area or volume convective and mechanical turbulence.      sources is allowed.

Revision as of 06:12, 11 March 2020

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IPRenewal NPEmails From: Ghosh, Tina Sent: Monday, January 31, 2011 10:48 AM To: Stuyvenberg, Andrew

Subject:

FW: Modeling Review - Indian Point Attachments: Modeling Review Document 6 14 10.doc Follow Up Flag: Follow up Flag Status: Flagged From: Jones, Joe A [1]

Sent: Tuesday, June 15, 2010 3:53 PM To: Palla, Robert; Ghosh, Tina Cc: Bixler, Nathan E

Subject:

Modeling Review - Indian Point Bob and Tina, We have completed our review of the AERMOD and CalPuff models comparing characteristics to the MACCS2 model.

Joe Schelling, one of our MACCS2 modelers, did the research on this and he and Nate iterated the document a couple of times.

Please let us know if you have any questions regarding this review.

Thanks Joe 1

Hearing Identifier: IndianPointUnits2and3NonPublic_EX Email Number: 2295 Mail Envelope Properties (6F9E3C9DCAB9E448AAA49B8772A448C55EE2C75CCD)

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FW: Modeling Review - Indian Point Sent Date: 1/31/2011 10:48:04 AM Received Date: 1/31/2011 10:48:05 AM From: Ghosh, Tina Created By: Tina.Ghosh@nrc.gov Recipients:

"Stuyvenberg, Andrew" <Andrew.Stuyvenberg@nrc.gov>

Tracking Status: None Post Office: HQCLSTR01.nrc.gov Files Size Date & Time MESSAGE 569 1/31/2011 10:48:05 AM Modeling Review Document 6 14 10.doc 109634 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

Recipients Received: Follow up

Severe Accident Mitigation Analysis Modeling Plan 6/14/2010 Objective The objective of this plan is to determine the feasibility, and if appropriate, the level of effort required to use the AERMOD and CALPUFF models in the same capacity MACCS2 is used to perform consequence modeling in terms of dose, contamination, and economic cost for severe accident mitigation alternatives (SAMA) analyses. AERMOD and CALPUFF are preferred and recommended by the U.S. Environmental Protection Agency for modeling air dispersion and air quality [1,2]. As air dispersion and air quality models, AERMOD and CALPUFF include models of contaminant dispersion and deposition that produce contaminant concentrations at various receptor locations as a function of time. MACCS2 models dispersion and deposition of a radioactive plume released from a nuclear power plant, and includes models of radioactive decay and ingrowth, ground contamination, dose consequences to the public for defined emergency response, and economic impacts of the release.

MACCS2 Overview The purpose of the MACCS2 code is to simulate the impact of severe accidents at nuclear power plants on the surrounding environment. The principal phenomena considered in MACCS2 are atmospheric transport, mitigative actions based on dose projection, dose accumulation by a number of pathways, including food and water ingestion, early and latent health effects, and economic costs [3].

MACCS2 models atmospheric dispersion and transport, and includes models for deposition, weathering, resuspension, and radioactive decay. A Gaussian plume model is used to model plume dispersion during downwind transport. Scaling factors are used in MACCS2 to model effects of surface roughness on plume dispersion. Statistical distributions of consequence measures that depict the range and probability of consequences are generated by MACCS2 in terms of complementary cumulative distribution functions (CCDFs).[4] These distributions are generated using stratified Monte Carlo sampling of combinations of representative sets of source terms, weather sequences, and exposed populations. Radioactive decay and ingrowth, and dry and wet aerosol deposition processes are modeled. Economic effects models in MACCS2 are intended to estimate the direct offsite costs resulting from a reactor accident and include costs resulting from both short-term and long-term protective actions [3].

The principal phenomena considered in MACCS2 are atmospheric transport using a Gaussian plume model, short-term and long-term dose accumulation through several pathways (including cloudshine, groundshine, inhalation, deposition onto the skin, and food and water ingestion), mitigative actions based on dose projection, early and latent health effects, and economic costs. The following phenomena can be incorporated within a single calculation:

Release characteristics; Meteorological sampling; Atmospheric dispersion and deposition; Exposure pathways and duration; Protective actions and dose mitigation; Movement of populations as cohorts; Individual and population doses; and Health and economic consequences.

MACCS2 has three major components, ATMOS, EARLY, and CHRONC. Of these components, only ATMOS, which treats dispersion and deposition using a Gaussian plume model, has similarities to AERMOD and CALPUFF. The EARLY and CHRONC modules are used to model emergency phase events and radiological consequences and economic costs of response actions, which are not considered in the functionality of AERMOD and CALPUFF.

ATMOS calculates the dispersion and deposition of material released to the atmosphere as a function of downwind distance, and uses a Gaussian plume model with Pasquill-Gifford dispersion parameters. ATMOS treats the following phenomena:

building wake effects, buoyant plume rise, plume dispersion during transport, wet and dry deposition, and radioactive decay and ingrowth [4].

EARLY models the time period immediately following a radioactive release, referred to as the emergency phase, which may extend up to one week after the first plume reaches any downwind location. User-specified scenarios may include evacuation, sheltering, and dose-dependent relocation. Dose calculations from early exposure consider five pathways: cloudshine, cloud inhalation, groundshine, resuspension inhalation, and skin dose from deposition onto skin. Acute doses and lifetime dose commitments are calculated [4].

CHRONC simulates events following the emergency-phase time period.

CHRONC calculates the number of health effects resulting from direct exposure to contaminated materials as well as health effects caused by subsequent consumption of contaminants. It calculates mitigative actions taken to reduce doses to the public, including decontamination, interdiction, and condemnation of property. CHRONC calculates the economic costs of these long-term protective actions as well as the costs from the emergency response actions modeled during the emergency phase [4].

EPA Regulatory Atmospheric Modeling Codes Two code systems recommended by the U.S. Environmental Protection Agency (EPA) for use in regulatory atmospheric modeling, and required for use for several programs are the AERMOD and CALPUFF modeling systems [1,2]. The EPA Support Center for Regulatory Atmospheric Modeling website provides the following basic descriptions of these modeling systems [1]:

AERMOD Modeling System - A steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain.

CALPUFF Modeling System - A non-steady-state puff dispersion model that simulates the effects of time- and space-varying meteorological conditions on pollution transport, transformation, and removal. CALPUFF can be applied for long-range transport and for complex terrain.

AERMOD Overview AERMOD was designed for short range (up to 50 km) dispersion from stationary sources, and includes modeling of surface terrain on the behavior of air pollution plumes and of building downwash effects. A Gaussian plume model is used [5]. AERMOD can model exponential decay. (The default regulatory option forces use of a 4 hr half life for SO2 in an urban source, and does not allow for exponential decay for other applications

[6].) Multiple sources from a single point can be modeled, and there are several options for specifying an array of receptor locations. Only a single value of halflife can be used in a given run [7]. The original version of the AERMOD model did not include algorithms to handle the gravitational settling and removal by dry deposition of particulates, or scavenging and removal by wet deposition of gases and particulates [8].

However, the AERMOD User Guide Addendum 09292 describes the later inclusion of dry and wet deposition algorithms for both particulate and gaseous emissions [10]. No dose pathway, dose mitigation (KI ingestion, sheltering, or evacuation), or economic models appear to be included in AERMOD.

CALPUFF Overview CALPUFF is proposed by the EPA for applications involving long-range transport, which is typically defined as transport over distances beyond 50 km, and requires approval by the relevant reviewing authorities for EPA regulatory applications involving transport distances less than 50 km [11]. A puff model may be used for most applications where a plume model is appropriate, but the technical decision on using a puff model should be based on whether the straight-line, steady-state assumptions on which a plume model is based are valid [11]. The EPA approved version of the CALPUFF System includes Version 5.8 - Level 070623 of CALPUFF and includes changes through MCB-D. Wet and dry deposition, and chemical transformation are modeled. No radioactive decay and ingrowth, dose pathway, dose mitigation (e.g.,

evacuation), or economic models are included in CALPUFF.

A summary comparison of the dispersion and deposition models of the ATMOS component of MACCS2, AERMOD, and CALPUFF are shown in Table 1. More detailed summary information on the latter two codes from Appendix A to Appendix W of 40 CFR Part 51 is shown in Appendix A.

Table 1. Summary Comparison of Atmospheric Dispersion and Deposition Models Parameter MACCS2/ATMOS AERMOD CALPUFF Plume Model Non-steady-state Steady-state Gaussian Non-steady-state Gaussian plume with plume model Lagrangian Gaussian multiple plume puff model; segments; Wind shear puff split; Plume expansion Briggs model; factor for meander; Partial penetration; Briggs model for Buoyant and buoyant plume rise momentum rise; Stack tip effects; Vertical wind shear Dispersion Two models: No user input Five models, Pasquill-Gifford including P-G stability class sigma-y and sigma-z; Time-based dispersion function Building Wake and Building wake Stack-tip downwash; Building downwash Terrain Effects entrainment; Surface terrain effects by two methods; Surface terrain effects (via surface roughness Applicable to rough or modeled with scaling length) complex terrain; factor Simulates changes in the flow and dispersion rate induced by terrain features Wet Deposition Exponential function Wet particulate and Empirical scavenging of rain duration and gaseous deposition model as function of intensity pollutant and precipitation type Dry Deposition Source depletion by Dry particulate and Resistance model particle size gaseous deposition dependent deposition velocity Meteorological Weather bin or Surface boundary Hourly wind/temp on Sampling random sampling of layer and profile 3D grid, w/2D annual data; variables; parameters Specification of Hourly time periods mixing layer height; 15-min, 30-min, or hourly time periods Material Sources Point or area source Multiple sources; Time varying point, w/multiple plume point, volume, area, line, volume, and area segments, aerosol and line; sources; sizes, and isotopic Variable emission Variable emission components rates rates Parameter MACCS2/ATMOS AERMOD CALPUFF Receptor Locations Polar grid centered on Multiple receptors; Essentially unlimited facility; Discrete, polar or gridded or discrete Up to 35 radial Cartesian grid receptors intervals; networks; Up to 64 compass Variable receptor directions; height Up to 7 receptors per grid Range 0.05 to 9999 km; Up to 50 km 10s of m to 100s of km Decay and Ingrowth Radioactive decay and Single exponential Linear removal and daughter ingrowth decay chemical conversion over six generations All three codes use a type of Gaussian dispersion model. AERMOD uses the simplest Gaussian representation, which is a steady-state plume; MACCS2 also uses a plume model, but the wind speed, stability class, and precipitation rate can change as the plume moves through the grid. CALPUFF uses a Gaussian puff model, which allows wind direction to change along the course of the plume.

An important distinction between these codes is that AERMOD and CALPUFF were specifically designed to treat chemical air pollutants. Because of this, they treat removal of the pollutants by chemical reaction but do not handle radioactive decay with daughter ingrowth. On the other hand, MACCS2 was specifically designed to treat radioactive air pollutants. It treats radioactive decay and daughter ingrowth for decay chains up to a length of six.

An approach to addressing the objective of this plan is to evaluate whether or not output generated by AERMOD and CALPUFF could be used as input to a post-processing routine to model radioactive decay and dose pathway processes, emergency phase relocation actions, and economic costs. That is, AERMOD and CALPUFF account for plume dispersion and deposition, and provide material concentrations at receptor locations. Approximation would be needed to model radioactive decay with daughter ingrowth during atmospheric transport for a large set of parents and daughters, and the corresponding adjustment made to deposited concentrations. An approach to modeling cloudshine effects would also be needed to ensure that predictions are not underestimated. From the deposited material concentrations, it may be possible to develop a set of dose conversion factors to account for various uptake pathways. The most difficult implementation would be to account for the interaction between time-dependent plume concentrations and evacuating public. Deposited material concentrations could be used to estimate economic costs for mitigative actions.

However, the mitigative actions, such as decontamination of property, are coupled with public doses. As a result, a coupled model is required to properly treat these effects.

Unlike MACCS2, neither AERMOD nor CALPUFF appear to have options for generating statistical distributions of consequences for variations in source terms, meteorology, or populations. Alternatively, it may be possible to incorporate these modeling functions in the codes directly.

Developing, testing, producing quality assurance (QA) documentation, and obtaining EPA approval for either AERMOD or CALPUFF in the context of nuclear reactor accidents would likely require considerable effort over a period of several years.

Some of the steps involved are shown in the following graphic.

AERMOD Output For each averaging period (1, 3, 8, or 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or 1 month), concurrent averages for all receptors for each day of data processed are generated. Receptor networks are printed first, followed by concurrent averages for each source group. Optional output files include POSTFILE, a file of concurrent (raw) results at each receptor. Appendix D of the AERMOD User Guide shows for the POSTFILE option a file including X and Y coordinates of the receptor location, receptor height, averaging period, source group ID, and either the date variable for the end of the averaging period or the number of hours in the period for period averages [9].

CALPUFF Output CALPUFF output files include one-hour averaged concentrations at gridded and discrete receptor locations for selected species and of wet and dry deposition fluxes; hourly reports of mass fluxes into and out of regions, and of mass changes for all species, are also produced. The CALPOST postprocessor program averages and reports concentrations or wet/dry fluxes based on hourly data in the CALPUFF output file [12].

Summary The objective of this plan is to determine the feasibility, and if appropriate, the level of effort required to use the AERMOD and CALPUFF models in the same capacity as MACCS2 for performing consequence modeling in terms of dose, health effects, land contamination, and economic cost for SAMA analyses. Because AERMOD and CALPUFF do not include models for emergency response, radioactive decay and ingrowth, radiological health effects, mitigative actions, or economic costs, code revision or development of post-processing utilities would be needed to utilize either of these codes to model nuclear reactor accident consequences in a manner similar to MACCS2.

Statistical sampling of parameter distributions is also a feature of MACCS2 that is not available in AERMOD or CALPUFF. Developing, testing, and acquiring acceptance of the results produced by these approaches would involve significant effort. Model assumptions and constraints needed for these utilities may limit the accuracy/fidelity of the results obtained.

References

1. Preferred/Recommended Models, Technology Transfer Network, Support Center for Regulatory Atmospheric Modeling, U.S. Environmental Protection Agency, http://www.epa.gov/scram001/dispersion_prefrec.htm, accessed May 6, 2010.
2. Appendix A to Appendix W of Part 51 - Summaries of Preferred Air Quality Models, Federal Register, Vol. 70, No. 216, Nov. 9, 2005.
3. Jow, H-N, J.L. Sprung, J.A. Rollstin, L.T. Ritchie, D.I. Chanin, MELCOR Accident Consequence Code System (MACCS) Model Description, NUREG/CR-4691, SAND86-1562, Vol. 2, February, 1990.
4. Chanin, D, M.L. Young, J. Randall, and K. Jamali, Code Manual for MACCS2:

Volume 1, Users Guide, NUREG/CR-6613, SAND97-0594, Vol. 1, May, 1998.

5. Table 1, AERMOD: Latest Features and Evaluation Results, EPA-454/R-03-003, June 2003. (aermod_mep.pdf)
6. Users Guide for the AMS/EPA Regulatory Model - AERMOD (Under Revision), EPA-454/B-03-001, U.S. Environmental Protection Agency, September 2004, p. 3-3.
7. Users Guide for the AMS/EPA Regulatory Model - AERMOD (Under Revision), EPA-454/B-03-001, U.S. Environmental Protection Agency, September 2004, p. 3-8.
8. Users Guide for the AMS/EPA Regulatory Model - AERMOD (Under Revision), EPA-454/B-03-001, U.S. Environmental Protection Agency, September 2004, p. 3-37.
9. Users Guide for the AMS/EPA Regulatory Model - AERMOD (Under Revision), EPA-454/B-03-001, U.S. Environmental Protection Agency, September 2004, Appendix D.
10. Addendum, Users Guide for the AMS/EPA Regulatory Model - AERMOD, (EPA-454/B-03-001, September 2004), U.S. Environmental Protection Agency, October 2009, p. 20.
11. Question 1.1.1., CALPUFF FAQs Answers, CALPUFF Modeling, The Atmospheric Studies Group at TRC, http://www.src.com/calpuff/FAQ-answers.htm#1.1.1 , accessed 4/29/2010.
12. Scire, J.S. D.G. Strimaitis, and R.J. Yamartino, A Users Guide for the CALPUFF Dispersion Model (Version 5), Earth Tech, Inc., January 2000.

Appendix A. Key Features of Refined Air Quality Models Parameter AERMOD1 CALPUFF1 Type of Model AERMOD is a steadystate plume model, (1) CALPUFF is a nonsteadystate time using Gaussian distributions in the and spacedependent Gaussian puff vertical and horizontal for stable model. CALPUFF treats primary conditions, and in the horizontal for pollutants and simulates secondary convective conditions. The vertical pollutant formation using a concentration distribution for convective parameterized, quasilinear chemical conditions results from an assumed bi conversion mechanism. Pollutants Gaussian probability density function of treated include SO2, SO42, NOX (i.e., NO +

the vertical velocity. NO2), HNO3, NO3, NH3, PM-10, PM-2.5, toxic pollutants and others pollutant species that are either inert or subject to quasilinear chemical reactions. The model includes a resistancebased dry deposition model for both gaseous pollutants and particulate matter. Wet deposition is treated using a scavenging coefficient approach. The model has detailed parameterizations of complex terrain effects, including terrain impingement, sidewall scraping, and steepwalled terrain influences on lateral plume growth. A subgridscale complex terrain module based on a dividing streamline concept divides the flow into a lift component traveling over the obstacle and a wrap component deflected around the obstacle.

(2) The meteorological fields used by CALPUFF are produced by the CALMET meteorological model. CALMET includes a diagnostic wind field model containing parameterized treatments of slope flows, valley flows, terrain blocking effects, and kinematic terrain effects, lake and sea breeze circulations, a divergence minimization procedure, and objective analysis of observational data. An energybalance scheme is used to compute sensible and latent heat fluxes and turbulence parameters over land surfaces. A profile method is used over water. CALMET contains interfaces to prognostic meteorological models such as the Penn State/NCAR Mesoscale Model (e.g., MM5; Section 12.0, ref. 86),

as well as the RAMS, Ruc and Eta models.

Parameter AERMOD1 CALPUFF1 Pollutant Types AERMOD is applicable to primary CALPUFF may be used to model gaseous pollutants and continuous releases of pollutants or particulate matter that are toxic and hazardous waste pollutants. inert or which undergo quasilinear Chemical transformation is treated by chemical reactions, such as SO2, SO42, simple exponential decay. NOX (i.e., NO + NO2), HNO3, NO3, NH3, PM-10, PM-2.5 and toxic pollutants. For regional haze analyses, sulfate and nitrate particulate components are explicitly treated.

SourceReceptor AERMOD applies userspecified locations CALPUFF contains no fundamental Relationships for sources and receptors. Actual limitations on the number of sources or separation between each source receptors. Parameter files are provided receptor pair is used. Source and that allow the user to specify the receptor elevations are user input or are maximum number of sources, determined by AERMAP using USGS DEM receptors, puffs, species, grid cells, terrain data. Receptors may be located vertical layers, and other model at userspecified heights above ground parameters. Its algorithms are designed level. to be suitable for sourcereceptor distances from tens of meters to hundreds of kilometers.

Parameter AERMOD1 CALPUFF1 Plume Behavior (1) In the convective boundary layer Momentum and buoyant plume rise is (CBL), the transport and dispersion of a treated according to the plume rise plume is characterized as the equations of Briggs (1975) for non superposition of three modeled plumes: downwashing point sources, Schulman The direct plume (from the stack), the and Scire (1980) for line sources and indirect plume, and the penetrated point sources subject to building plume, where the indirect plume downwash effects using the Schulman accounts for the lofting of a buoyant Scire downwash algorithm, and Zhang plume near the top of the boundary (1993) for buoyant area sources and layer, and the penetrated plume point sources affected by building accounts for the portion of a plume that, downwash when using the PRIME due to its buoyancy, penetrates above building downwash method. Stack tip the mixed layer, but can disperse downwash effects and partial plume downward and reenter the mixed layer. penetration into elevated temperature In the CBL, plume rise is superposed on inversions are included. An algorithm to the displacements by random convective treat horizontallyoriented vents and velocities (Weil et al., 1997). stacks with rain caps is included.

(2) In the stable boundary layer, plume rise is estimated using an iterative approach, similar to that in the CTDMPLUS model (see A.5 in this appendix).

(3) Stacktip downwash and buoyancy induced dispersion effects are modeled.

Building wake effects are simulated for stacks less than good engineering practice height using the methods contained in the PRIME downwash algorithms (Schulman, et al., 2000). For plume rise affected by the presence of a building, the PRIME downwash algorithm uses a numerical solution of the mass, energy and momentum conservation laws (Zhang and Ghoniem, 1993).

Streamline deflection and the position of the stack relative to the building affect plume trajectory and dispersion.

Enhanced dispersion is based on the approach of Weil (1996). Plume mass captured by the cavity is wellmixed within the cavity. The captured plume mass is reemitted to the far wake as a volume source.

(4) For elevated terrain, AERMOD incorporates the concept of the critical dividing streamline height, in which flow below this height remains horizontal, and flow above this height tends to rise up and over terrain (Snyder et al., 1985).

Plume concentration estimates are the weighted sum of these two limiting plume states.

Parameter AERMOD1 CALPUFF1 However, consistent with the steady state assumption of uniform horizontal wind direction over the modeling domain, straightline plume trajectories are assumed, with adjustment in the plume/receptor geometry used to account for the terrain effects.

Horizontal Winds Vertical profiles of wind are calculated A threedimensional wind field is for each hour based on measurements computed by the CALMET and surfacelayer similarity (scaling) meteorological model. CALMET relationships. At a given height above combines an objective analysis ground, for a given hour, winds are procedure using wind observations with assumed constant over the modeling parameterized treatments of slope flows, domain. The effect of the vertical valley flows, terrain kinematic effects, variation in horizontal wind speed on terrain blocking effects, and sea/lake dispersion is accounted for through breeze circulations. CALPUFF may simple averaging over the plume depth. optionally use single station (horizontallyconstant) wind fields in the CTDMPLUS, AERMOD or ISCST3 data formats.

Vertical Wind In convective conditions, the effects of Vertical wind speeds are not used Speed random vertical updraft and downdraft explicitly by CALPUFF. Vertical winds velocities are simulated with a bi are used in the development of the Gaussian probability density function. In horizontal wind components by both convective and stable conditions, CALMET.

the mean vertical wind speed is assumed equal to zero.

Horizontal Gaussian horizontal dispersion Turbulencebased dispersion coefficients Dispersion coefficients are estimated as continuous provide estimates of horizontal plume functions of the parameterized (or dispersion based on measured or measured) ambient lateral turbulence computed values of v. The effects of and also account for buoyancyinduced building downwash and buoyancy and building wakeinduced turbulence. induced dispersion are included. The Vertical profiles of lateral turbulence are effects of vertical wind shear are developed from measurements and included through the puff splitting similarity (scaling) relationships. algorithm. Options are provided to use Effective turbulence values are PasquillGifford (rural) and McElroy determined from the portion of the Pooler (urban) dispersion coefficients.

vertical profile of lateral turbulence Initial plume size from area or volume between the plume height and the sources is allowed.

receptor height. The effective lateral turbulence is then used to estimate horizontal dispersion.

Parameter AERMOD1 CALPUFF1 Vertical In the stable boundary layer, Gaussian Turbulencebased dispersion Dispersion vertical dispersion coefficients are coefficients provide estimates of vertical estimated as continuous functions of plume dispersion based on measured or parameterized vertical turbulence. In computed values of w. The effects of the convective boundary layer, vertical building downwash and buoyancy dispersion is characterized by a bi induced dispersion are included. Vertical Gaussian probability density function, dispersion during convective conditions and is also estimated as a continuous is simulated with a probability density function of parameterized vertical function (PDF) model based on Weil et turbulence. Vertical turbulence profiles al. (1997). Options are provided to use are developed from measurements and PasquillGifford (rural) and McElroy similarity (scaling) relationships. These Pooler (urban) dispersion coefficients.

turbulence profiles account for both Initial plume size from area or volume convective and mechanical turbulence. sources is allowed.

Effective turbulence values are determined from the portion of the vertical profile of vertical turbulence between the plume height and the receptor height. The effective vertical turbulence is then used to estimate vertical dispersion.

Chemical Chemical transformations are generally Gas phase chemical transformations are Transformation not treated by AERMOD. However, treated using parameterized models of AERMOD does contain an option to treat SO2 conversion to SO42 and NO chemical transformation using simple conversion to NO3, HNO3. Organic exponential decay, although this option aerosol formation is treated. The is typically not used in regulatory POSTUTIL program contains an option to applications, except for sources of sulfur repartition HNO3 and NO3 in order to dioxide in urban areas. Either a decay treat the effects of ammonia limitation.

coefficient or a half life is input by the user. Note also that the Plume Volume Molar Ratio Method (subsection 5.1) and the Ozone Limiting Method (subsection 5.2.4) and for pointsource NO2 analyses are available as nonregulatory options.

Physical Removal AERMOD can be used to treat dry and Dry deposition of gaseous pollutants and wet deposition for both gases and particulate matter is parameterized in particles. terms of a resistancebased deposition model. Gravitational settling, inertial impaction, and Brownian motion effects on deposition of particulate matter is included. CALPUFF contains an option to evaluate the effects of plume tilt resulting from gravitational settling. Wet deposition of gases and particulate matter is parameterized in terms of a scavenging coefficient approach.

1 Appendix A to Appendix W of Part 51 - Summaries of Preferred Air Quality Models, Federal Register, Vol. 70, No. 216, November 9, 2005.

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