Screen3 View. Contents. Page 1

Transcription

1 Screen3 View Contents Introduction What is EPA's SCREEN3 Model? What is the Screen3 View Interface? Toollbar Buttons Preliminary Considerations Source Inputs Screen3 Options Running SCREEN3 Model Graphic Results Editor Technical Support Page 1

2 ... Page 2 What is EPA's SCREEN3 Model? The SCREEN model was developed to provide an easy-to-use method of obtaining pollutant concentration estimates. These estimates are based on the document "Screening Procedures for Estimating The Air Quality Impact of Stationary Sources" (EPA 1995). SCREEN3, version 3.0 of the SCREEN model, can perform all the single source short-term calculations in the EPA screening procedures document, including : Estimating maximum ground-level concentrations and the distance to the maximum. Incorporating the effects of building downwash on the maximum concentrations for both the near wake and far wake regions (see Building Downwash Option). Estimating concentrations in the cavity recirculation zone (see Building Downwash Option). Estimating concentrations due to inversion break-up and shoreline fumigation (see Fumigation Option). Determining plume rise for flare releases. EPA s SCREEN3 model can also : Incorporate the effects of simple elevated terrain on maximum concentrations (see Simple Terrain Option). Estimate 24-hour average concentrations due to plume impaction in complex terrain using the VALLEY model 24-hour screening procedure (see Complex Terrain Option). Model simple area sources using a numerical integration approach (See Area Source Inputs ). Be used to model the effects of simple volume sources using a virtual point source procedure (See Volume Source Inputs). Calculate the maximum concentration at any number of user-specified distances in flat or elevated simple terrain, including distances out to 100 km for long-range transport (see Discrete Distances Option). Examine a full range of meteorological conditions, including all stability classes and wind speeds to find maximum impacts (See Choice of Meteorology). Include the effects of buoyancy-induced dispersion (BID). Explicitly calculates the effects of multiple reflections of the plume off the elevated inversion and off the ground when calculating concentrations under limited mixing conditions. EPA s SCREEN3 model will not be able to do the following :

3 Explicitly determine maximum impacts from multiple sources, except for the procedure to handle multiple nearby stacks by merging emissions into a single "representative" stack (See Merged Parameters for Multiple Stacks). With the exception of the 24-hour estimate for complex terrain impacts, the results from SCREEN are estimated maximum 1-hour concentrations. Page 3

4 Screen3 View Contents Introduction Source Inputs Title Source Type Dispersion Coefficient Source Inputs Point Source Inputs Flare Release Inputs Area Source Inputs Volume Source Inputs Screen3 Options Running SCREEN3 Model Graphic Results Editor Technical Support Page 4

5 ... Title Title : A one line title, up to 79 characters, must be provided for each source run. This is a descriptive title for the project and it will appear in the output file generated by EPA's SCREEN3 model. Page 5

6 ... Source Type : Source Type For each run, the user has to select one of the four options that best identifies the source being modeled: Point : Localized sources such as stacks and isolated vents. Flare : Localized, point source, where a high release heat rate occurs, such as in flares and flames. Area : Sources where emissions are spread over an area such as a landfill. Volume : Three-dimensional type source such as fugitive leaks on an industrial facility. Page 6

7 ... Dispersion Coefficient Dispersion Coefficient : Either Urban or Rural dispersion coefficients can be selected for the source being modeled. In Screen3 View, the default is the Rural option. The classification of a site as urban or rural should be based on one of the procedures described on the EPA document Guidelines on Air Quality Models (Revised) (1987) (EPA 1987). See Urban/Rural Classification for these procedures. Page 7

8 Urban/Rural Classification The following was compiled from Section 2.4 of "SCREEN3 Model User's Guide" (EPA 1995b).and Section of the "Guideline on Air Quality Models (Revised)" (EPA 1987). The selection of either urban or rural dispersion coefficients should be based upon the land use procedure or population density procedure : 1. Land Use Procedure : Circumscribe a 3 km radius circle, Ao, about the source using meteorological land use typing scheme, (a) if land use types I1, I2, C1, R2, and R3 account for 50 % or more of Ao, select Urban option, (b) otherwise use the Rural option. 2. Population Density Procedure : Compute the average population density, p, per square kilometer with Ao as defined above, (a) If p > 750 people/km2, select the Urban option, (b) If p <= 750 people/km2, select the Rural option. Of the two methods above, the land use procedure is considered a more definitive criteria. The population density procedure should be used with caution and should not be applied to highly industrialized areas where the population density may be low and thus a rural classification would be indicated, but the area is sufficiently built-up so that the urban land use criteria would be satisfied. In this case, the classification should already be "urban" and urban dispersion parameters should be used. References : (1) U.S. Environmental Protection Agency, 1995a. SCREEN3 Model User's Guide, EPA-454/B U.S. Environmental Protection Agency. Research Triangle Park, NC (Section 2.4). (2)..U.S. Environmental Protection Agency, 1995b. Guideline On Air Quality Models (Revised), EPA-450/ R. U.S. Environmental Protection Agency. Research Triangle Park, NC (Section 8.2.8). Page 8

9 ... Point Source Inputs Point Source Inputs : For a Point source, the user must provide the following information : See Unit Buttons for explanation on how to convert the Unit System (Metric or English) for each source input. Emission Rate [g/s or lb/h] : Enter the emission rate of the pollutant. Stack Height [m or ft] : Enter the stack height above ground. Stack Inside Diameter [m or ft] : Enter the stack inside diameter. Stack Gas Exit Velocity [m/s or lb/h] or Stack Gas Exit Flow Rate [m3/s or ACFM] : Either the stack gas exit velocity or the stack gas exit flow rate should be given. In Screen3 View, the user has to select the Velocity or Flow Rate option from the drop-down list box and select the desired unit by clicking the unit button. The exit velocity can be determined from the following formula: Vs = 4 V p ds**2 Vs = Exit Velocity V = Flow Rate ds = Stack Inside Diameter Page 9 Stack Gas Exit Temperature [K or F] : Enter the temperature of the released gas. If this data is not available, it may be approximated from guidelines that yield typical values for those parameters for existing sources. Ambient Air Temperature (default 293 K) [K or F] : Enter the average atmospheric temperature in the vicinity of the source. Ambient air temperature data are collected hourly at NWS (National Weather Service) stations and are available from NCDC or from the SCRAM BBS. If no ambient temperature data are available, assume a default value of 293

10 degrees Kelvin (K). For non-buoyant releases, the user should input the same value for the stack temperature and ambient temperature. Receptor Height Above Ground [m or ft] : This may be used to model impacts at flagpole receptors. A flagpole receptor is defined as any receptor located above ground level, e.g., to represent the roof or balcony of a building. The default value is assumed to be 0.0 m (i.e., ground-level receptors). Options Available for Point Sources : Building Downwash Complex Terrain Simple Terrain Automated Distances Discrete Distances Choice of Meteorology Fumigation Page 10

11 ... Area Source Inputs Area Source Parameters : The Area source can be approximated by a rectangular area. Areas which have irregular shapes can be simulated by dividing the area source into multiple rectangles that approximate the geometry of the area source. The following are the inputs requested for Area sources : See Unit Buttons for explanation on how to change the Unit System (Metric or English) for each source input. Page 11 Emission Rate [g/(s-m2) or lb/(h-ft2)] : Enter the emission rate of the pollutant. The emission rate for area sources is input as an emission rate per unit area. Source Release Height [m or ft] : Enter the source release height above ground. Larger Side Length of Rectangular Area [m or ft] : Enter the larger side of the rectangular source. Smaller Side Length of Rectangular Area [m or ft] : Enter the smaller side of the rectangular source. Receptor Height Above Ground [m or ft] : This may be used to model impacts at flagpole receptors. A flagpole receptor is defined as any receptor which is located above ground level, e.g., to represent the roof or balcony of a building. The default value is assumed to be 0.0 m (i.e., ground-level receptors). Search Through Range of Wind Directions? (Yes or No) : Since the concentration at a particular distance downwind from a rectangular area is dependent on the orientation of the area relative to the wind direction, the SCREEN model provides the user with two options for treating wind direction. In Screen3 View these two options are represented by the Yes and No options. Yes : By selecting this option, EPA s SCREEN model will search through a range of wind

12 directions to find the maximum concentration. The range of directions used in the search is determined from a set of look-up tables based on the aspect ratio of the area source, the stability category, and the downwind distance. This is the regulatory default option and should be used for most applications. No : By selecting this option, the user must specify a wind direction orientation relative to the long axis of the rectangular area. This option may be used to estimate the concentration at a particular receptor location relative to the long area. If this option is selected, then the next input option Wind Direction Relative to Long Dimension becomes available and user must input a wind direction. See explanation on next input option. Wind Direction Relative to Long Dimension [deg] : This option is only available if user has selected the No for the Search Through Range of Wind Directions? option. In this input field, the user has to input a wind direction orientation relative to the long axis of the rectangular area. Options Available for Area Sources : Automated Distances (for Flat Simple Terrain only) Discrete Distances (for Flat Simple Terrain only) Choice of Meteorology Note 1 : The following options are not available when modeling Area sources: Complex Terrain, Elevated Simple Terrain, Building Downwash, and Fumigation. Page 12

13 Screen3 View Contents Introduction Source Inputs Screen3 Options Available SCREEN Options Building Downwash Option Complex Terrain Option Simple Terrain Option Automated Distances Option Discrete Distances Option Choice of Meteorology Fumigation Option Running SCREEN3 Model Graphic Results Editor Technical Support Page 13

14 ... Simple Terrain Option Simple Elevated Terrain or Simple Flat Terrain Option : When modeling simple terrain you are given the option of modeling either: Simple Flat Terrain : where terrain heights are assumed not to exceed stack base elevation. If this option is used, then terrain height is considered to be 0.0 m. Simple Elevated Terrain : where terrain heights exceed stack base but are below stack height. If this option is used, then the terrain height above stack base should be specified. If terrain heights above physical stack height are entered, then Screen3 View gives a warning message and the user has to re enter a valid height value. To model Simple Flat Terrain or Simple Elevated Terrain, you can choose either or both of the distance options (Automated Distances or Discrete Distances). Make sure to select the appropriate option (Flat Terrain or Elevated Terrain). Each selection requires different inputs (see Automated Distances Option and Discrete Distances Option). When modeling with Simple Terrain screening (Flat Terrain or Elevated Terrain), the user is given the option of selecting from three choices of meteorology (see Choice of Meteorology). Page 14 Note 1: The simple elevated terrain screening procedure assumes that the plume elevation above sea level is not affected by the elevated terrain. Concentration estimates

15 are made by reducing the calculated plume height by the user-supplied terrain height above the stack base. Neither the plume height nor the terrain height are allowed to go below zero. (EPA 1995b) Note 2: For relatively uniform elevated terrain, or as a "first cut" conservative estimate of terrain effects, you should input the maximum terrain elevation (above stack base) within 50 km of the source, and exercise the automated distance array option out to 50 km. (EPA 1995b) Note 3 : For isolated terrain features a separate calculation can be made using the discrete distance option for the distance to the terrain feature. The terrain height should be input as the maximum height of the feature above stack base. (EPA 1995b) Note 4 : Where terrain heights vary with distance from the source, the SCREEN model can be run on each of several concentric rings using the minimum and maximum distance inputs of the automated distance option. You can then use the maximum terrain elevation above the stack base within each ring for terrain height input. (EPA 1995b) Note 5 : In SCREEN, terrain heights are not allowed to decrease with distance. If terrain decreasing with distance can be justified for a particular source, then the distance rings would have to be modeled using separate SCREEN runs, and the results combined. The overall maximum concentration would then be the controlling value. The optimum ring sizes will depend on how the terrain heights vary with distance. As a "first cut" it is suggested that ring sizes of about 5 km be used (i.e., 0-5 km, 5-10 km, etc.). The application of SCREEN to evaluating the effects of elevated terrain should be done in consultation with the permitting agency. (EPA 1995b) Other Topics : Building Downwash Option Complex Terrain Option Automated Distances Option Discrete Distances Option Choice of Meteorology Fumigation Option Page 15

16 ... Automated Distances Option Automated Distances Option : The Automated Distances option gives the user the option of using a pre-selected array of 50 distances ranging from 100 m out to 50,000 m (50 km) using the following increments: For the Automated Distances option, the SCREEN model calculates the maximum concentration across a range of meteorological conditions for the minimum distance given. SCREEN then computes the concentration for each distance in the array larger than the minimum and less than or equal to the maximum. SCREEN also uses an iteration routine to determine the maximum value associated with that distance to the nearest meter. To model with Automated Distances option, follow the steps below: Step 1 - Check the Automated Distances box, if this box is not already selected. Since this option is the most commonly used by air modelers, when you first start a Screen3 View project, the Automated Distances check box will be already selected for you. If you do not want this option you have to deselect it. Step 2 - Input the following information on the Automated Distances tab, depending if you have chosen the Flat Terrain or Elevated Terrain option: For Flat Terrain, input the following : Page 16

17 Automated Distances tab Min. Distance [m or ft]: For most applications, this distance should correspond to the minimum distance to the plant boundary or fenceline. The smallest value allowed is 1.0 meter, for Area sources is 0.0 meter, and the maximum 50,000 meters. Max. Distance [m or ft]: This value should be large enough to ensure that the maximum concentration beyond the fenceline is determined. The smallest value allowed is 1.0 meter, for Area sources is 0.0 meter, and the largest value allowed is 50,000 meters (50 km). Screen3 View will make sure you do not enter values outside this range and that the maximum distance value be always greater than the minimum distance value. For Elevated Terrain, input the following (option not available for Area sources) : Page 17 Automated Distances tab Terrain Height Above Stack Base [m or ft]: This is the height of the terrain above the stack base. This value should always be smaller or equal to the effective stack height. Screen3 View will alert you if the height you enter is in a valid range. Minimum Distance [m or ft]: For most applications, this distance should correspond to the minimum distance to the plant boundary or fenceline. The smallest value allowed is 1.0

18 meter. Maximum Distance [m or ft]: This value should be large enough to ensure that the maximum concentration beyond the fenceline is determined. The smallest value allowed is 1.0 meter and the largest value allowed is 50,000 meters (50 km). Screen3 View will make sure you do not enter values outside this range and that the maximum distance value you entered is greater than the minimum distance value. Note 1 : For Area sources, distances are measured from the center of the rectangular area. Any value for the minimum distance can be given since concentrations within the area source can be estimated. Note 2 : For Volume sources, concentrations within the volume source cannot be estimated. The SCREEN model will give a concentration of zero for distances, measured from the center of the volume, of less than 2.15 σyo (σyo=initial lateral dimension). Note 3 : The user can input the minimum site boundary distance as the minimum distance for calculation and obtain a concentration estimate at the site boundary and beyond, while ignoring distances less than the site boundary. Note 4 : It is recommended that the maximum distance be set sufficiently large initially to ensure that the maximum concentration is found. This distance will depend on the source, however, the user can input a distance of 50,000 m (50 km) to examine the entire array. Other Topics : Building Downwash Option Complex Terrain Option Simple Terrain Option Discrete Distances Option Choice of Meteorology Fumigation Option Page 18

19 ... Discrete Distances Option Discrete Distances Option : The Discrete Distances option allows the user to find the maximum impact at specific locations of interest, such as nearby residences, hospitals, or schools, and may also be used for long-range transport estimates out to 100 km. Any number of distances (equal or greater than 1.0 m) can be input and the maximum concentration for each distance will be calculated. To model with Discrete Distances option, follow the steps below : Step 1: Check the Discrete Distances box. Step 2: Input the following information on the Discrete Distances tab, depending if you have selected simple Flat Terrain or simple Elevated Terrain option: For simple Flat Terrain, input the following : Discrete Distances tab Page 19 Distance from Source [m or ft]: The smallest value allowed is 1.0 meter, for Area sources

20 is 0.0 meter, and the maximum value is 100,000 meters (100 km). For simple Elevated Terrain, input the following (option not available for Area sources): Discrete Distances tab Terrain Height Above Stack Base [m or ft]: This is the height of the terrain above stack base. This value should be always smaller or equal to the effective stack height. Screen3 View will alert you if the height you enter is in a valid range. Distance from Source [m or ft]: The smallest value allowed is 1.0 meter and the maximum value is 100,000 meters (100 km). Screen3 View will make sure you do not enter values outside this range. Note 1 : SCREEN model will accepts distances out to 100 km for long-range transport estimates. However, for distances greater than 50 km, SCREEN sets the minimum 10-meter wind speed at 2 m/s to avoid unrealistic transport times. (EPA 1995b) Note 2 : For Area sources, distances are measured from the center of the rectangular area. Any value for the minimum distance can be given since concentrations within the area source can be estimated. Other Topics : Building Downwash Option Complex Terrain Option Simple Terrain Option Automated Distances Option Choice of Meteorology Fumigation Option Page 20

21 Screen3 View Contents Introduction Source Inputs Screen3 Options Running SCREEN3 Model Project Status Detais Graphic Results Editor Technical Support Page 21

22 ... Project Status Dialog Box You can only run EPA's SCREEN3 model when you have finished inputting all the necessary information for your project. Follow the steps below to Run your project: 1. Click on the [Run] button located on the menu toolbar or select Run from the menu bar. The Run command is available to you at any time, if you are either in the Source Inputs or in the Screen3 Options window. 2. The Run command displays the Project Status dialog box, which contains: the full path and name of the input and output file, a summary of all options you have selected for this run, and a message that identifies if your project is complete or not. If any information is missing, the [Run] button is disabled and the [Details] button is enabled allowing you to see the missing information. Page If your project is complete, note that the message on the bottom panel of the Project Status dialog box reads Your Project Input is Complete. You can RUN Now!!!. 4. When you press the [Run] button located on the Project Status dialog box, a DOS window appears showing EPA s SCREEN3 model processing the input file. When the run is

23 completed the message on the Project Status dialog box changes to Click [Close] when SCREEN3 finish running. Click the [Close] button to see the SCREEN3 results. 5. If your project is not complete, than the message on the bottom panel reads Your Project is NOT Complete!! See Details". Press the [Details] button. In the Details dialog box, check what information is missing, input the missing information and then run the project. Page 23

24 Screen3 View Contents Introduction Source Inputs Screen3 Options Running SCREEN3 Model Graphic Results Introduction to the Graphical Results Toolbar Buttons List of Available Plots Options Buttons Editor Technical Support Page 24

25 ... List of Available Plots In the Graphic Results window, a list of the available plots can be found on the drop-down list box located below the toolbar menu. To display the plot on the screen, select one of the available plots from the list. 1. Click on the drop down list located right below the toolbar to see the list of plots you have available for the current project. The plot displayed on the chart area is the first plot of the list. The plot description contained on the list is defined by : a) The first part defines the option selected (e.g., Complex Terrain, Automated Distances) followed by Vs. (versus) Concentration. b) The second part defines the terrain height being used (e.g., 30. m). For the Complex Terrain Vs. Concentration plot, the terrain height is variable. 2. Click on all the items of the drop down list to see the plots available. You can also open the drop down list and use the up and down arrow keys on your keyboard to scroll through the list of available plots. You can only display one plot at a time. Page 25

26 Screen3 View Contents Introduction Source Inputs Screen3 Options Running SCREEN3 Model Graphic Results Editor Available Options How to Read SCREEN3 Output Files Technical Support Page 26

27 ... How to Read SCREEN3 Output Files Follow the steps below and look at the correspondent numbers on the figures for explanation on how to read SCREEN3 output files. The output file shown below is for a point source example that incorporates building downwash calculations. 1. Date and time that the model was executed. 2. SCREEN model version number and version date. 3. User-specified title for the run. 4. Summary of the inputs for the particular source being modeled. In this example, simple terrain calculations were performed for a point source using urban dispersion coefficients and considering the effects of building downwash. 5. Calculated values for the buoyancy flux and momentum flux parameters. 6. SCREEN identifies which choice of meteorology was selected for this run. In this example, Full Meteorology was selected. Steps 7 to 20 (SCREEN AUTOMATED DISTANCES) Steps 21 to 25 (CAVITY CALCULATION & SUMMARY OF RESULTS) Page 27