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Screen3 Model User's Guide - Environmental Protection Agency

1. SIMPLE TERRAIN 715 3 800 0 BUILDING CAVITY 1 3168 142 DIST CAVITY LENGTH BUILDING CAVITY 2 1691 101 DIST CAVITY LENGTH REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS 24 Figure 3 SCREEN Point Source Example with Building Downwash Page 2 of 2 25 This page is intentionally left blank 26 Figure 4 Enter Velocity m s or Flow Rate or m 3 s Exit Enter Stack Gas Exit Temperature Enter Ambient Temperature Enter Receptor Height Above Ground m Enter Urban Rural Option U Urban R Rural Flow Chart of Inputs and Outputs for SCREEN Point Source Page 1 of 2 Consider No Downwash Enter Y or N Yes Enter Building Height m Enter Horizontal Building Dimension m Min Enter Horizontal Building Dimension m Max 27 Make Complex Ter No 24 hour Calc Enter Y or N Yes Print Out Plume Height and Dist to Final Rise m Enter Terrain Height m and Distance to Terrain m ls Terrain No Height gt 0 Yes Print Complex Terrain 24 hr Concentration Out More SCREEN with Yes Simp Terrain Enter Y or Enter Choice of Meteorology Enter Choice of Meteorology Full Met 2 Sin
2. Z M DWASH 100 0000 0 0 0 0 00 00 00 NA 200 0000 0 0 0 0 00 00 00 NA 300 631 6 1 1 5 21 480 0 125 11 90 71 82 09 SS 400 517 4 1 1 5 2 1 480 0 140 59 118 85 113 59 55 500 494 6 6 10 2 0 10000 0 113 08 50 21 50 05 SS 600 578 0 6 10 2 010000 0 113 08 59 27 54 62 55 700 638 4 6 10 2 010000 0 113 08 68 06 59 18 55 800 715 3 6 10 2 010000 0 113 08 76 59 65 44 55 22 900 699 4 6 10 2 0 10000 0 113 08 84 89 68 33 SS 1000 681 9 6 10 2 0 10000 0 113 08 92 97 71 13 SS MAXIMUM 1 CONCENTRATION OR BEYOND 100 M 800 715 3 6 1 0 2 010000 0 113 08 76 59 65 44 SS DWASH MEANS NO CALC MADE CONC 0 0 DWASH NO MEANS NO BUILDING DOWNWASH USED DWASH HS MEANS HUBER SNYDER DOWNWASH USED DWASH SS MEANS SCHULMAN SCIRE DOWNWASH USED DWASH NA MEANS DOWNWASH NOT APPLICABLE X 3 LB Figure 3 SCREEN Point Source Example with Building Downwash Page 1 of 2 23 XXX CAVITY CALCULATION 1 XXX CAVITY CALCULATION 2 CONC UG M 3 3168 CONC UG M 3 1691 CRIT WS 10M 5 3 32 CRIT WS 10M 5 7 77 CRIT WS HS 5 5 26 CRIT WS HS M S 12 32 DILUTION WS M S 2 63 DILUTION WS M S 6 16 CAVITY HT 114 88 CAVITY 105 20 CAVITY LENGTH 142 41 CAVITY LENGTH 101 30 ALONGWIND DIM M 80 00 ALONGWIND DIM 100 00 SUMMARY OF SCREEN MODEL RESULTS CALCULATION MAX CONC DISTTO TERRAIN PROCEDURE UG M 3
3. 454 95 004 SCREEN3 Model User s Guide U S ENVIRONMENTAL PROTECTION AGENCY Office of Air Quality Planning and Standards Emissions Monitoring and Analysis Division Research Triangle Park North Carolina 27711 September 1995 DISCLAIMER The information in this document has been reviewed in its entirety by the U S Environmental Protection Agency EPA and approved for publication as an EPA document Any mention of trade names products or services does not convey and should not be interpreted as conveying official EPA approval endorsement or recommendation ii The SCREEN3 Model User s Guide is update to Appendix A of Screening Procedures for Estimating the Air Quality Impact of Stationary Sources EPA 1988 which was later revised and published as a separate document EPA 1995a The SCREEN3 model includes several modifications and enhancements to the original SCREEN model including updates to the code to ensure consistency with the dispersion algorithms in the Industrial Source Complex ISC3 model EPA 19955 Also three new non regulatory options were added to the code Although attempts are made to thoroughly check computer programs with a wide variety of input data errors are occasionally found Any suspected errors and technical questions regarding the use of the SCREEN3 model should be directed to Chief Air Quality Modeling Group OAQPS EMAD MD 14 Research Triangle Park NC 27
4. SCREEN can not explicitly determine maximum impacts from multiple sources except for the procedure to handle multiple nearby stacks by merging emissions into a single representative Stack Section 2 2 The user is directed to the MPTER Pierce and Turner 1980 or ISC EPA 1995b models on EPA s Support Center for Regulatory Air Models SCRAM Bulletin Board System BBS to model short term impacts for multiple sources With the exception of the 24 hour estimate for complex terrain impacts the results from SCREEN are estimated maximum 1 hour concentrations To handle longer period averages the screening procedures document contains recommended adjustment factors to estimate concentrations out to 24 hours from the maximum 1 hour value Section 4 2 Step 5 For seasonal or annual averages Section 4 4 of the screening procedures document contains a procedure using hand calculations but the use of ISCLT EPA 1995b or another long term model on the SCRAM BBS is recommended 1 6 How will SCREEN results compare to hand calculations from the document The SCREEN model is based on the same modeling assumptions that are incorporated into the screening procedures and nomographs and for many sources the results will be very comparable with estimated maximum concentrations differing by less than about 5 percent across a range of source characteristics However there are a few differences of which the user should be aware For some sources
5. o 1 where 3 concentration g m emission rate g s 3 141593 stack height wind speed m s lateral dispersion parameter m vertical dispersion parameter m receptor height above ground m plume centerline height m mixing height m summation limit for multiple reflections of plume off of the ground and elevated inversion usually lt 4 H IO x I N 6 MC C we H N lt 43 Note that for stable conditions and or mixing heights greater than or equal to 10 000m unlimited mixing is assumed and the summation term is assumed to be zero Equation 1 is used to model the plume impacts from point sources flare releases and volume releases in SCREEN The SCREEN volume source option uses a virtual point source approach as described in Volume II Section 1 2 2 of the ISC model user s guide EPA 1995b The user inputs the initial lateral and vertical dimensions of the volume source as described in Section 2 7 above The SCREEN model uses a numerical integration algorithm for modeling impacts from area sources as described in Volume II Section 1 2 3 of the ISC model user s guide EPA 1995b area source is assumed to be a rectangular shape and the model can be used to estimate concentrations within the area 3 2 Worst Case Meteorological Conditions SCREEN examines a range of stability classes and wind speeds to identify the worst case meteorological conditions i
6. on PCs allows for the redirection of input that is normally provided via the keyboard to be read from a file instead As an example to run the sample problem provided on the disk one would type SCREEN3 EXAMPLE DAT at the DOS prompt The SCREEN model will then read the responses to its prompts from the EXAMPLE DAT file rather than from the keyboard The output from this run will be stored in a file called SCREEN OUT which can then be compared with the EXAMPLE OUT file provided on the program disk The file containing the redirected input data may be given any valid DOS pathname To facilitate the creation of the input file for the SCREEN model SCREEN has been programmed to write out all inputs provided to a file called SCREEN DAT during execution Therefore at the completion of a run if the user types SCREEN3 SCREEN DAT the last run will be duplicated exactly Alternatively the SCREEN DAT file may be edited as an ASCII file using a text or line editor and selected input parameters changed before rerunning the model Since the original SCREEN DAT file will overwritten each time the model is run it is advisable to save the modified inputs under a different file name Some cautions are needed regarding the use of redirected input with SCREEN Because of the way some input errors are handled by SCREEN the SCREEN DAT file may contain some of the errors from the original input While SCREEN DAT should still reproduce the corr
7. The momentum flux which is used in estimating plume rise for building downwash effects is calculated from Fa v d T 4T 7 The ISC user s guide EPA 1995b describes the equations used to estimate buoyant plume rise and momentum plume rise for both unstable neutral and stable conditions Also described are transitional plume rise and how to estimate the distance to final rise Final plume rise is used in SCREEN for all cases with the exception of the complex terrain screening procedure and for building downwash effects The buoyant line source plume rise formulas that are used for the Schulman Scire downwash scheme are described in Section 1 1 4 11 of Volume II of the ISC user s guide EPA 19955 These formulas apply to sources where lt H 0 54 For sources subject to downwash but not meeting this criterion the downwash algorithms of Huber and Snyder EPA 1995b are used which employ the Briggs plume rise formulas referenced above 3 4 Dispersion Parameters The formulas used for calculating vertical C and lateral dispersion parameters for rural and urban sites are described in Section 1 1 5 of Volume II of the ISC user s guide EPA 19955 3 5 Buoyancy Induced Dispersion 47 Throughout the SCREEN model with the exception of the Schulman Scire downwash algorithm the dispersion parameters o and o are adjusted to account for the effects of buoyancy induced dispersion as follows Y Qui um
8. particularly taller sources with greater buoyancy the differences in estimated concentrations will be larger with the hand calculation exceeding the SCREEN model result by as much as 25 percent These differences are described in more detail below The SCREEN model can provide estimated concentrations for distances less than 100 meters down to one meter as in other regulatory models whereas the nomographs used in the hand calculations are limited to distances greater than or equal to 100 meters The SCREEN model is also not limited to plume heights of 300 meters whereas the nomographs are In both cases caution should be used in interpreting results that are outside the range of the nomographs In addition SCREEN examines a full range of meteorological conditions including all stability classes and wind speeds see Section 3 to find maximum impacts whereas to keep the hand calculations tractable only a subset of meteorological conditions stability classes A C and E or F likely to contribute to the maximum concentration are examined The use of a full set of meteorological conditions is required in SCREEN because maximum concentrations are also given as a function of distance and because A C and E or F stability may not be controlling for sources with building downwash not included in the hand calculations SCREEN explicitly calculates the effects of multiple reflections of the plume off the elevated inversion and off the grou
9. EMISSION RATE G S 1000 00 FLARE STACK HEIGHT M 100 0000 TOT HEAT RLS CAL S 100000 08 RECEPTOR HEIGHT M 0000 URBAN RURAL OPTION RURAL EFF RELEASE HEIGHT M 110 1150 BUILDING HEIGHT 0000 MIN HORIZ BLDG DIM M 0000 HORIZ BLDG DIM M 0000 BUOY FLUX 165 803 M 4 S 3 MOM FLUX 101 103 M 4 S 2 XX FULL METEOROLOGY SCREEN AUTOMATED DISTANCES TERRAIN HEIGHT 0 M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES DIST CONC UIOM USTK MIX PLUME SIGMA SIGMA UG M 3 STAB M S CM S HTM Y M Z M DWASH 250 7733E 04 5 1 0 2 310000 0 233 54 38 05 36 05 NO 300 2501 03 1 3 0 3 5 960 0 344 28 78 46 57 07 NO 400 1 283 1 3 0 3 5 960 0 344 28 100 36 80 87 NO 500 66 54 1 3 0 3 5 960 0 344 28 121 51 113 75 NO 600 407 0 1 3 0 3 5 960 0 344 28 142 09 161 96 NO 700 741 2 1 3 0 3 5 960 0 344 28 162 21 220 50 NO 800 944 9 1 1 5 1 8 579 5 578 45 210 37 308 17 900 1303 1 1 5 1 8 579 5 578 45 231 47 386 36 NO 1000 1449 1 1 5 1 8 579 5 578 45 247 92 473 16 NO 1100 1448 1 1 5 1 8 579 5 578 45 263 50 571 19 NO 1200 1387 1 1 5 1 8 579 5 578 45 279 21 680 86 NO 1300 1315 1 1 5 1 8 579 5 578 45 295 03 802 07 29 1400 1248 1 1 5 1 8 579 5 578 45 310 90 934 77 1500 1187 1 1 5 1 8 579 5 578 45 326 80 1078 93 1600 1132 1 1 5 1 8 579 5 578 45 342 72 1234 58 1700 1082 1 1 5 1 8 579 5 578 45 358 64 1401 74 N
10. Onlock 1982 have shown that the TIBL factor A ranges from about 2 to 6 For screening purposes A is conservatively set equal to 6 since this will minimize the distance to plume TIBL intersection and therefore tend to maximize the concentration estimate As with the inversion break up case the distance to maximum ground level concentration is determined by iteration The equation used for the shoreline fumigation case is Xnax h 2072 7 6 2 Xs 16 where downwind distance to maximum concentration m x shortest distance from source to shoreline m h plume centerline height m vertical dispersion parameter incorporating buoyancy induced dispersion m Plume height is based on the assumed F stability and 2 5 m s wind 51 Speed and the dispersion parameter incorporates the effects of buoyancy induced dispersion x is less than 200m then no shoreline fumigation calculation is made since the plume may Still be influenced by transitional rise and its interaction with the TIBL is more difficult to model The maximum ground level concentration due to shoreline fumigation X is also calculated from Turner s 1970 Equation 5 2 gt X Q 2n u o h 8 h 2o 14 with o and o incorporating the effects of buoyancy induced dispersion Even though the calculation of Xw above accounts for the distance from the source to the shoreline in x extra caution should be
11. Source Gaussian Dispersion Algorithm EPA 600 8 86 042 U S Environmental Protection Agency Research Triangle Park NC Available only from NTIS NTIS Accession Number PB87 145 363 Pierce T E and D B Turner 1980 User s Guide for MPTER A Multiple Point Gaussian Dispersion Algorithm With Optional Terrain Adjustment EPA 600 8 80 016 U S Environmental Protection Agency Research Triangle Park NC Randerson D 1984 Atmospheric Boundary Layer In Atmospheric Science and Power Production Randerson D ed DOE TIC 27601 U S Department of Energy Washington D C Schulman L L and Scire J S 1993 Building Downwash Screening Modeling for the Downwind Recirculation Cavity Air and Waste August 1122 1127 Turner D B 1964 A Diffusion Model for an Urban Area Journal of Applied Meteorology 3 83 91 Turner D B 1970 Workbook of Atmospheric Dispersion Estimates Revised Sixth printing Jan 1973 Office of Air Programs Publication No AP 26 60
12. Urban Enter V R Rural N or No STOP Figure 10 Flow Chart of Inputs and Outputs for SCREEN Volume Source 42 3 TECHNICAL DESCRIPTION Most of the techniques used in the SCREEN model are based on assumptions and methods common to other EPA dispersion models For the sake of brevity lengthy technical descriptions that are available elsewhere are not duplicated here This discussion will concentrate on how those methods are incorporated into SCREEN and on describing those techniques that are unique to SCREEN 3 1 Basic Concepts of Dispersion Modeling SCREEN uses a Gaussian plume model that incorporates source related factors and meteorological factors to estimate pollutant concentration from continuous sources is assumed that the pollutant does not undergo any chemical reactions and that no other removal processes such as wet or dry deposition act on the plume during its transport from the source The Gaussian model equations and the interactions of the source related and meteorological factors are described in Volume of the ISC user s guide EPA 1995b and in the Workbook of Atmospheric Dispersion Estimates Turner 1970 The basic equation for determining ground level concentrations under the plume centerline is X Q 212 0 0 exp 340 21 Soy exp z h o 21 2 exp X z h 2Nz o 21 exp z h 2Nz o 21 exp z h 2Nz o 21 exp z h 2Nz
13. Urban rural option U urban rural Wind direction search option if no specify desired angle Note that the emission rate for area sources is input as an emission rate per unit area in units of g s m These units are consistent with the ISCST model 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 The first option which should be used for most applications of SCREEN and is the regulatory default is for the model to search through a range of wind 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 The SCREEN model also provides the user an option to specify a wind direction orientation relative to the long axis of the rectangular area The second option may be used to estimate the concentration at a particular receptor location relative to the area The output table for area sources includes the wind direction associated with the maximum concentration at each distance The user has the same options for handling distances and the same choices of meteorology as described above for point sources 16 but no complex terrain elevated simple terrain building downwash or
14. e the combination of wind speed and stability that results in the maximum ground level concentrations The wind speed and Stability class combinations used by SCREEN are given in Table 2 10 meter wind speeds given in Table 2 are adjusted to Stack height by SCREEN using the wind profile power law exponents given in Table 3 1 of the screening procedures document For release heights of less than 10 meters the wind speeds listed in Table 2 are used without adjustment For distances greater than 50 km available with the discrete distance option SCREEN sets 2 m s as the lower limit for the 10 meter wind speed to avoid unrealistic transport times Table 2 includes some cases that may not be considered standard stability class wind speed combinations namely E with winds less than 2 m s and F with winds greater than 3 m s The combinations of E and winds of 1 1 5 m s are often excluded because the algorithm developed by Turner 1964 to determine stability class from routine National Weather Service NWS observations excludes cases of E stability for wind speeds less than 4 knots 2 m s These combinations are included in SCREEN because they are valid combinations that could appear in a data set using on site meteorological data with another stability class method wind speed of 6 knots the highest speed for F stability in Turner s scheme measured at a typical NWS anemometer height of 20 feet 6 1 meters corresponds to a 10 meter win
15. equal to 20 m s then a cavity concentration is calculated otherwise the cavity concentration is assumed to be zero Concentrations within the cavity X are estimated by the following approximation Hosker 1984 X Q 1 5 u 10 where emission rate g s A H W cross sectional area of the building normal to the wind m 48 crosswind dimension of the building m u wind speed m s For u a value of one half the stack heiqht critical wind speed is used but not greater than 10 m s and not less than 1 m s Thus the calculation of X is linked to the determination of a critical wind speed The concentration X is assumed to be uniform within the cavity cavity length measured from the lee side of the building is estimated by the following Hosker 1984 1 for short buildings L h lt 2 11 1 0 B W h 2 for long buildings L h gt 2 1 75 W 12 1 0 0 25 W h where h building height m alongwind building dimension m crosswind building dimension m 2 0 3 7 0715 and 0 15 0 305 L h V X LI The equations above for cavity height concentration cavity length are all sensitive to building orientation through the terms L W and A Therefore the entire cavity procedure is performed for two orientations first with the minimum horizontal dimension alongwind and second with the maximum horizon
16. fumigation calculations are made for area sources Distances are measured from the center of the rectangular area Since the numerical integration algorithm can estimate concentrations within the area source the user can enter any value for the minimum distance Figure 7 shows an example of SCREEN for an area source using both the automated and discrete distance options Figure 8 provides a flow chart of inputs options and outputs for area sources 2 7 Volume Source Example The fourth source type option in SCREEN is for volume sources which is selected by entering V or v for source type The volume source algorithm is based on a virtual point Source approach and may be used for non buoyant sources whose emissions occupy some initial volume The inputs requested for volume sources are as follows Volume Source Inputs Emission rate g s Source release height m Initial lateral dimension of volume m Initial vertical dimension of volume m Receptor height above ground m Urban rural option U urban rural The user must determine the initial dimensions of the volume source plume before exercising the SCREEN model volume source Table 1 provides guidance on determining these inputs Since the volume source algorithm cannot estimate concentrations within the volume source the model will give a concentration of zero for distances measured from the center of the volume of less than 2 15 o Figure 9 shows an example
17. or N Distance No Yes with New Ter Ht Enter Y or N Bldg Make Print Out Print Out Yes Downwash No Fumigation Inversion Cavity Considered Calcs Enter Break up Resuts Y or N Fumigation Conc 8 Dist Make Shoreine Fumi Cak Y Print Out Enter Min Yes Maximum Distance Shoreline from Source Fumigation to Shoreline Con amp Dist STOP Figure 6 Flow Chart of Inputs and Outputs for SCREEN Flare Release Page 2 of 2 34 09 07 95 12 00 00 SCREEN3 MODEL RUN VERSION DATED 95250 AREA SOURCE EXAMPLE SIMPLE TERRAIN INPUTS SOURCE TYPE EMISSION RATE G S M 2 250000 02 SOURCE HEIGHT M 5 0000 LENGTH OF LARGER SIDE M 200 0000 LENGTH OF SMALLER SIDE M 200 0000 RECEPTOR HEIGHT M 0000 URBAN RURAL OPTION MODEL ESTIMATES DIRECTION TO CONCENTRATION BUOY FLUX 000 M 4 S 3 FLUX 000M 4 S 2 FULL METEOROLOGY K K K SCREEN AUTOMATED DISTANCES TERRAIN HEIGHT 0 M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES DIST C0MC UIOM USTK MIX HT PLUME MAX DIR M UG M 3 STAB M S M S M HT M DEG 150 4067 05 5 1 0 1 010000 0 5 00 43 200 3784E 05 5 1 0 1 0 100000 5 00 45 300 2430 05 5 1 0 1 0 100000 5 00 45 400 1755 05 5 1 0 1 0 10000 0 5 00 45 500 1356 05 5 1 0 1 0 100000 5 00 45 600
18. than the plume height h then the mixing height used in calculating the concentration is set equal to h 1 For stable conditions the mixing height is set equal to 10 000m to represent unlimited mixing 3 3 Plume Rise for Point Sources The use of the methods of Briggs to estimate plume rise are discussed in detail in Section 1 1 4 of Volume II of the ISC user s guide EPA 1995b These methods are also incorporated in the SCREEN model Stack tip downwash is estimated following Briggs 1973 p 4 46 for all sources except those employing the Schulman Scire downwash algorithm Buoyancy flux for non flare point sources is calculated from gv d T T 47 5 which is described in Section 4 of the screening procedures document and is equivalent to Briggs 1975 p 63 Equation 12 Buoyancy flux for flare releases is estimated from F 1 66 x 10 x H 6 where H is the total heat release rate of the flare cal s This formula was derived from Equation 4 20 of Briggs 1969 assuming T 293K p 1205 g m 0 24 cal gK and that the sensible heat release rate 0 0 45 The sensible heat rate is based on the assumption that 55 percent of the total heat released is lost due to radiation Leahey and Davies 1984 The buoyancy flux for flares is calculated in SCREEN by assuming effective stack parameters of v 20 m s T 1 273K and solving for an effective stack diameter d 9 88 x 10 Q
19. the prompts should be self explanatory Section 3 provides background technical information as a reference for those who want to know more about how SCREEN makes certain calculations The discussion in Section 3 is intended to be as brief as possible with reference to other documents for more detailed descriptions 1 2 Purpose of SCREEN The SCREEN model was developed to provide an easy to use method of obtaining pollutant concentration estimates based on the screening procedures document By taking advantage of the rapid growth in the availability and use of personal computers PCs the SCREEN model makes screening calculations accessible to a wide range of users 1 3 What is needed in order to use SCREEN SCREEN will run on an IBM PC compatible personal computer with at least 256K of RAM You will need at least one 5 1 4 inch double sided double density 360K or a 5 1 4 inch high density 1 2MB disk drive The program will run with or without a math coprocessor chip Execution time will be greatly enhanced with a math coprocessor chip present about a factor of 5 in computer time and will also benefit from the use of a hard disk drive SCREEN will write a date and time to the output file provided that a real time clock is available 1 4 What will SCREEN do SCREEN runs interactively on the PC meaning that the program asks the user a series of questions in order to obtain the necessary input data and to determine which opt
20. 1091 05 5 1 0 1 0 100000 5 00 45 700 9028 5 1 0 1 0 1000000 5 00 45 800 7629 5 1 0 1 010000 5 00 45 900 6559 5 1 0 1 0 1000000 5 00 44 1000 5718 5 1 0 1 0 1000000 5 00 45 MAXIMUM 1 CONCENTRATION OR BEYOND 150 M 1 010000 0 5 00 45 168 4178 05 5 1 0 35 Figure 7 SCREEN Area Source Example Page 1 of 2 36 262626 26 XC 26 26 26 26 XC R 26 26 SCREEN DISCRETE DISTANCES TERRAIN HEIGHT 0 M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES DIST C0MC UI0M USTK MIX HT PLUME MAX DIR M UG M 3 STAB M S M S M HT M DEG 5000 718 1 5 1 0 1 010000 0 5 00 38 10000 321 3 5 1 0 1 010000 0 5 00 1 20000 150 4 5 1 0 1 010000 0 5 00 31 50000 71 25 4 1 0 1 0 320 0 5 00 11 29 gt F gt F 26 XC 2 XC R 26 26 26 XC SUMMARY SCREEN MODEL RESULTS CALCULATION MAX CONC DIST TO TERRAIN PROCEDURE UG M 3 MAX M HT M SIMPLE TERRAIN 4178 05 168 0 REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS 37 Figure 7 SCREEN Area Source Example Page 2 of 2 38 START Enter Source Type A for Area Source Enter Emission Rate g s m 2 Enter Source Release Height m Enter Length of Larger Side tor Rectangular Area Enter Length of Smaller Side tor Rectan
21. 192 9 161 1 32 9 415 02 200 2000 284 3 284 3 192 9 0000 00 40 0 200 5000 91 39 91 39 192 9 0000 0 0 0 0 200 10000 37 36 37 36 192 9 0000 0 0 0 0 29 gt F gt F 26 XC 26 26 26 26 XC R 26 SUMMARY SCREEN MODEL RESULTS CALCULATION DISTTO TERRAIN PROCEDURE UG M 3 MAX M HT M COMPLEX TERRAIN 2843 2000 200 24 HR CONC 20 LLELLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLDLLLLLLLEL REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLDLLLLLLLEL Figure 2 SCREEN Point Source Example for Complex Terrain 21 09 07 95 12 00 00 XXX SCREEN3 MODEL RUN VERSION DATED 95250 POINT SOURCE EXAMPLE WITH BUILDING DOWNWASH SIMPLE TERRAIN INPUTS SOURCE TYPE POINT EMISSION RATE G S 100 000 STACK HEIGHT M 100 0000 STK INSIDE DIAM M 2 0000 STK EXIT VELOCITY M S 15 0000 STK GAS EXIT TEMP 450 0000 AMBIENT AIR TEMP 293 0000 RECEPTOR HEIGHT M 0000 URBAN RURAL OPTION URBAN BUILDING HEIGHT M 80 0000 MIN HORIZ BLDG DIM 80 0000 HORIZ BLDG DIM 100 0000 BUOY FLUX 51 319 M 4 S 3 MOM FLUX 146 500 M 4 S 2 FULL METEOROLOGY SCREEN AUTOMATED DISTANCES TERRAIN HEIGHT 0 M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES DIST CONC UIOM USTK MIX PLUME SIGMA SIGMA UG M 3 STAB M S M S M HTM
22. 711 Copies of the SCREEN3 model may be obtained from the National Technical Information Service 5 U S Department of Commerce 5285 Port Royal Road Springfield VA 22161 telephone 703 487 4650 or may be downloaded from the Support Center for Regulatory Air Models SCRAM Bulletin Board System BBS The SCRAM BBS may be accessed at 919 541 5742 Questions related to connecting to SCRAM should be directed to the TTN Helpline at 919 541 5384 111 ACKNOWLEDGEMENTS This report has been funded by the United States Environmental Protection Agency EPA under contract 68D00124 to Pacific Environmental Services Inc Mr Roger W Brode Pacific Environmental Services Inc is the principal contributor to the SCREEN3 Model User s PES Guide In addition this document was reviewed and commented upon by Mr Dennis G Atkinson EPA OAQPS Mr James L Dicke EPA OAQPS Revisions to EPA OAQPS and Mr John S Irwin the original SCREEN3 User s Guide were reviewed and commented upon by Dennis G Atkinson EPA OAQPS the SCREEN3 Work Assignment Manager and Mr Peter A Eckhoff EPA OAQPS iv PREFACE CONTENTS ACKNOWLEDGEMENTS FIGURES TABLES 1 INTRODUCTION l Overview of User S Guide Purpose of SCREEN What is needed in order to use SCREEN What will SCREEN do What will SCREEN not do How will SCREEN results compare to hand
23. A C and E or F may also not give the maximum concentration when building downwash is considered The second choice is to input a single stability class 1 2 B 6 F SCREEN will examine a range of wind speeds for that stability class only Using this option the user is able to determine the maximum concentrations associated with each of the individual procedures a c in Step 4 of Section 4 2 The third choice is to specify a single stability class and wind Speed The last two choices were originally put into SCREEN to facilitate testing only but they may be useful if particular meteorological conditions are of concern However they are not recommended for routine uses of SCREEN The mixing height used in SCREEN for neutral and unstable conditions classes A D is based on an estimate of the mechanically driven mixing height The mechanical mixing height z m is calculated Randerson 1984 as m 2 0 3 u f 2 where u friction velocity m s Coriolis parameter 9 374 x 107 s at 40 latitude Using a log linear profile of the wind speed and assuming a surface roughness length of about 0 3m u is estimated from the 10 meter wind speed U as IX 0 1 3 Substituting for u in Equation 2 we have 320 4 The mechanical mixing height is taken to be the minimum daytime mixing height To be conservative for limited mixing calculations if the value of z from Equation 3 is less
24. National Technical Information Service Springfield Virginia 22151 Briggs G A 1973 Diffusion Estimation for Small Emissions NOAA ATDL Contribution File No 79 Draft Oak Ridge TN Briggs G A 1975 Plume Rise Predictions In Lectures on Air Pollution and Environmental Impact Analysis Haugen D A ed American Meteorological Society Boston MA pp 59 111 Brode R W 1991 Comparison of SCREEN Model Dispersion Estimates with Estimates From a Refined Dispersion Model Seventh Joint Conference on Applications of Air Pollution Meteorology with A amp WMA 93 96 Burt E W 1977 Valley Model User s Guide EPA 450 2 77 018 U S Environmental Protection Agency Research Triangle Park NC Environmental Protection Agency 1977 Guidelines for Air Quality Maintenance Planning and Analysis Volume 10 Revised Procedures for Evaluating Air Quality Impact of New Stationary Sources EPA 450 4 77 001 OAQPS Number 1 2 029R Research Triangle Park NC Environmental Protection Agency 1983 Regional Workshops on Air Quality Modeling A Summary Report Addendum EPA 450 4 82 015 U S Environmental Protection Agency Research Triangle Park NC Environmental Protection Agency 1987a Guideline On Air Quality Models Revised and Supplement A EPA 450 2 78 027R U S Environmental Protection Agency Research Triangle Park NC Environmental Protection Agency 1987b Analysis and Evaluation of Statistical Coastal Fumi
25. O 1800 1036 1 1 5 1 8 579 5 578 45 374 55 1580 46 1900 993 9 1 1 5 1 8 579 5 578 45 390 43 1770 78 2000 957 5 1 1 0 1 2 813 6 812 62 432 95 1978 42 NO MAXIMUM 1 CONCENTRATION BEYOND 250 M 1046 1461 1 1 5 1 8 579 5 578 45 254 91 515 82 DWASH MEANS NO CALC MADE CONC 0 0 DWASH NO MEANS NO BUILDING DOWNWASH USED DWASH HS MEANS HUBER SNYDER DOWNWASH USED DWASHZSS MEANS SCHULMAN SCIRE DOWNWASH USED DWASH NA MEANS DOWNWASH NOT APPLICABLE X 3 LB Figure 5 SCREEN Flare Release Example Page 1 of 2 30 LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLEL SUMMARY OF SCREEN MODEL RESULTS CALCULATION MAX CONC DIST TERRAIN PROCEDURE UG M 3 SIMPLE TERRAIN 1461 1046 0 REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS K K K K K K K K K K K 31 Figure 5 SCREEN Flare Release Example Page 2 of 2 32 Type SCREENS to START Enter Source Type F for Flare Release Enter Emission Rate g s Enter Flare Release Height m Enter Total Heat Released cal s Enter Receptor Height Above Ground m Enter Urban Rural Option U Urban R Rural Consider No Downwash Enter Y or N Yes Enter Bullding Height m Enter Horizontal Building Dimension m Enter Horizo
26. OF pO hy e 8 Ou C 2 3 5 2 5 where Ah is the distance dependent plume rise Note that for inversion break up and shoreline fumigation distances are always beyond the distance to final rise and therefore Ah final plume rise 3 6 Building Downwash 3 6 1 Cavity Recirculation Region The cavity calculations are a revision of the procedure described in the Regional Workshops on Air Quality Modeling Summary Report Appendix C EPA 1983 and are based largely on results published by Hosker 1984 If non zero building dimensions are input to SCREEN for either point or flare releases then cavity calculations will be made as follows The cavity height h m is estimated based on the following equation from Hosker 1984 h hy 1 0 1 6 exp I 3L hj 9 where h building height m L alongwind dimension of the building m Using the plume height based on momentum rise at two building heights downwind including stack tip downwash a critical i e minimum stack height wind speed is calculated that will just put the plume into the cavity defined by plume centerline height cavity height The critical wind speed is then adjusted from Stack height to 10 meter using a power law with an exponent of 0 2 to represent neutral conditions no attempt is made to differentiate between urban or rural sites or different stability classes If the critical wind speed adjusted to 10 meters is less than or
27. OLLOWING DISTANCES DIST CONC UIOM USTK MIX PLUME SIGMA SIGMA M UG M 3 STAB M S M S M HT M Y M Z M DWASH 100 0000 0 0 0 00 00 00 200 239 5 6 1 0 1 010000 0 10 00 55 68 21 40 NO 300 224 1 6 1 0 1 010000 0 10 00 58 61 21 82 NO 400 209 1 6 1 0 1 010000 0 10 00 61 51 22 40 NO 500 195 7 6 1 0 1 010000 0 10 00 64 41 22 90 NO 600 183 8 6 1 0 1 010000 0 10 00 67 28 23 52 NO 700 173 0 6 1 0 1 010000 0 10 00 70 15 24 00 NO 800 163 2 6 1 0 1 010000 0 10 00 73 00 24 60 NO 900 154 4 6 1 0 1 010000 0 10 00 75 84 25 12 NO 1000 146 3 6 1 0 1 010000 0 10 00 78 66 25 64 NO MAXIMUM 1 CONCENTRATION OR BEYOND 100 M 109 257 5 6 1 0 1 010000 0 10 00 53 04 20 78 40 DWASH MEANS NO CALC MADE CONC 0 0 DWASH NO MEANS NO BUILDING DOWNWASH USED DWASH HS MEANS HUBER SNYDER DOWNWASH USED DWASH SS MEANS SCHULMAN SCIRE DOWNWASH USED DWASH NA MEANS DOWNWASH NOT APPLICABLE X 3 LB SUMMARY SCREEN MODEL RESULTS K K K CALCULATION DISTTO TERRAIN PROCEDURE UG M 3 SIMPLE TERRAIN 257 5 109 0 LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLEL REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS ig FR R R R RR R R R R R K K RER K K K K R K K K K K K K K K K K K Figure 9 SCREEN Volume Source Example 41 Type SCREENS to START Enter Choic
28. Source Characteristics Building Downwash Option Complex Terrain Option Simple Elevated or Flat Terrain Option Choice of Meteorology Automated Distance Array Option Discrete Distance Option Fumigation Option Rural Only Corresponding Section in Screening Procedures Document Section 4 5 1 Section 4 5 2 Section 4 2 Section 4 2 Step 4 Section 4 2 Step 4 Section 4 3 for Distances lt 50km Section 4 5 6 for Distances gt 50km Section 4 5 3 These options also apply to Area Sources Section 4 5 4 Figure 1 Point Source Options in SCREEN 19 09 07 95 12 00 00 SCREEN3 MODEL RUN VERSION DATED 95250 POINT SOURCE EXAMPLE WITH COMPLEX TERRAIN COMPLEX TERRAIN INPUTS SOURCE TYPE POINT EMISSION RATE G S 100 000 STACK HT M 100 0000 STACK DIAMETER M 2 5000 STACK VELOCITY M S 25 0000 STACK GAS TEMP 450 0000 AMBIENT AIR TEMP 293 0000 RECEPTOR HEIGHT M 0000 URBAN RURAL OPTION RURAL BUOY FLUX 133 643 4 5 3 MOM FLUX 635 851 4 5 2 FINAL STABLE PLUME HEIGHT 192 9 DISTANCE TO FINAL RISE M 151 3 VALLEY 24 HR CALCS SIMPLE TERRAIN 24 CALCS TERR MAX 24 HR PLUME HT PLUME HT HT DIST CONC CONC ABOVESTK CONC ABOVESTK U10M USTK M M UG M 3 UG M 3 BASE M UG M 3 HGT M SC M S 150 1000 243 4 243 4
29. W and the distance of the stack from the centerline is x producing a ratio of 4 Note that the ratio is always a positive number Ratios greater than 5 indicate that the stack is not on the roof x HL 5 Spouse 5 0 HL 5 0 56 25 necp reris 5 5 HL 4 NOTE PROGRAMMERS The SCREEN model executable provided SCRAM was compiled using the Microsoft FORTRAN Compiler Version 5 1 was compiled with the emulator library meaning that the executable file SCREEN3 EXE will run with or without a math coprocessor chip minimum of 256 KB of RAM is required to execute the model Provided in a compressed file on SCRAM are the executable file SCREEN3 EXE the FORTRAN source code files SCREEN3A FOR SCREEN3B FOR SCREEN3C FOR MAIN INC and DEPVAR INC a sample input file EXAMPLE DAT an associated output file EXAMPLE OUT and this document the SCREEN3 Model User s Guide in WordPerfect 5 1 format SCREEN3R WPF Also included is a READ ME file with instructions on extracting SCREEN The SCREEN model provided was compiled with the following Microsoft FORTRAN compile command FL FPi Gt FeSCREEN3 EXE SCREEN3A FOR SCREEN3B FOR SCREEN3C FOR where the FPi compile option specifies the emulator library and causes floating point operations to be processed using in line instructions rather than library CALLs us
30. above stack base If terrain heights above physical stack height are entered by the user for this option they are chopped off at the physical stack height The simple elevated terrain screening procedure assumes that the plume elevation above sea level is not affected by the elevated terrain Concentration estimates are made by reducing the calculated plume height by the user supplied terrain height above stack base Neither the plume height nor terrain height are allowed to go below zero The user can model simple elevated terrain using either or both of the distance options described below i e the automated distance array or the discrete distance option When the simple elevated terrain calculations for each distance option are completed the user will have the option of continuing simple terrain calculations for that option with a new terrain height For flat terrain the user will not be given the option to continue with a new terrain height For conservatism and to discourage the user from modeling terrain heights that decrease with distance the new terrain height for the automated distances cannot be lower than the previous height for that run The user is still given considerable flexibility to model the effects of elevated terrain below stack height across a wide range of situations For relatively uniform elevated terrain or as a first cut conservative estimate of terrain effects the user should input the maximum terrain elevatio
31. array option is used The option is terminated by entering a distance of zero 0 SCREEN will accept distances out to 100 km for long range transport estimates with the discrete distance option However for distances greater than 50 km SCREEN sets the minimum 10 meter wind speed at 2 m s to avoid unrealistic transport times 2 4 7 Fumigation Option Once the distance dependent calculations are completed SCREEN will give the user the option of estimating maximum concentrations and distance to the maximum associated with inversion break up fumigation and shoreline fumigation The option for fumigation calculations is applicable only for rural inland sites with stack heights greater than or equal to 10 meters within 3 000m onshore from a large body of water The fumigation algorithm also ignores any potential effects of elevated terrain Once all calculations are completed SCREEN summarizes the maximum concentrations for each of the calculation procedures considered Before execution is stopped whether it is after complex terrain calculations are completed or at the end of the simple terrain calculations the user is given the option of printing a hardcopy of the results Whether or not a hardcopy is printed the results of the session including all input data and concentration estimates are stored in a file called SCREEN OUT This file is opened by the model each time it is run If a file named SCREEN OUT already exists then its content
32. ban and rural refer to Section 8 2 8 of Appendix W to 40 CFR Part 51 Guideline on Air Quality Models Figure 1 presents the order of regulatory options within the 9 SCREEN model for point sources and is annotated with the corresponding sections from the screening procedures document In order to obtain results from SCREEN corresponding to the procedures in Step 4 of Section 4 2 the user should select the full meteorology option the automated distance array option and if applicable for the source the simple elevated terrain option The simple elevated terrain option would be used if the terrain rises above the stack base elevation but is less than the height of the physical stack These as well as the other options in Figure 1 are explained in more detail below A flagpole receptor is defined as any receptor which is located above local ground level e g to represent the roof or balcony of a building 2 4 1 Building Downwash Option There are two downwash options available with this model a regulatory and a non regulatory option Both are discussed below 2 4 1 1 Regulatory Building Downwash Option Following the basic input of source characteristics a SCREEN prompt asks if building downwash is to be considered and if so prompts for building height minimum horizontal dimension and maximum horizontal dimension in meters are presented The downwash screening procedure assumes that the building can be approximated by a si
33. by adding flags and a value to the line in the input file containing the source type input 1 9 What constitutes the requlatory default in SCREEN Regulatory default consists of 1 entering the appropriate input source characteristics 2 selecting the appropriate regulatory options see Figure 1 and 3 then using the recommended SCREEN defaults Discussion of the SCREEN inputs regulatory options and defaults can be found in Section 2 of this document and throughout Section 4 of the Screening Procedures document See References Regulatory default does not include the use of any of the three new non regulatory options mentioned in Section 1 8 2 TUTORIAL 2 1 What is needed e compatible with at least 256 bytes of RAM and 5 1 4 inch double sided double density or high density disk drive Diskette provided with SCREEN software or files downloaded from the SCRAM BBS e Hard or floppy disk drive minimum of 1 MB memory available Math coprocessor chip optional but recommended Blank diskette for use in making a backup copy of software 2 2 Setup on the PC Using the DISKCOPY command of DOS Disk Operating System or similar routine make a backup copy of the SCREEN software Store the original SCREEN software diskette in a safe location The DISKCOPY command will also format the blank disk if needed The following set up instructions assume that the user has a System with a hard disk drive an
34. calculations from the document How does SCREEN differ from PTPLU PTMAX and PTDIS What changes have been incorporated into SCREEN What constitutes regulatory default in SCREEN 2 TUTORIAL 2 OO OO What is needed Setup on the PC Executing the Model Point Source Example Flare Release Example Area Source Example Volume Source Example Non Regulatory Options 3 TECHNICAL DESCRIPTION UJ Q WW 0 N S Basic Concepts of Dispersion Modeling Worst Case Meteorological Conditions Plume Rise for Point Sources Dispersion Parameters Buoyancy Induced Dispersion Building Downwash Fumigation Complex Terrain 24 hour Screen 4 NOTE TO PROGRAMMERS 5 REFERENCES 111 1V vii Oe FIGURES Figure Page Te Point Source Options in SCREEN x 09 19 2 SCREEN Point Source Example for Complex Terrain 20 SCREEN Point Source Example with Building Downwash 21 4 Flow Chart of Inputs and Outputs for SCREEN Point Source Re Fist cst dr e IE 24 5 SCREEN Flare Release Example 26 6 Flow Chart of Inputs and Outputs for SCREEN Flare Release a omoare i w Wya x GRO X po 9 4 4 wo 28 7 SCREEN Area Source Example 30 8 Flow Chart of Inputs and Output
35. d speed of 4 m s under F stability Therefore the combination of F and 4 m s has been included 44 Table 2 Wind Speed and Stability Class Combinations Used by the SCREEN Model 10 m Wind Speed Stability m s Class 1 15 2 25 3 35 4 45 5 8 10 15 201 D ue qae GU SE I X3 cde det we D ques E dBe The user has three choices of meteorological data to examine The first choice which should be used in most applications is to use Full Meteorology which examines all six Stability classes five for urban sources and their associated wind speeds Using full meteorology with the automated distance array described in Section 2 SCREEN prints out the maximum concentration for each distance and the overall maximum and associated distance The overall maximum concentration from SCREEN represents the controlling 1 hour value corresponding to the result from Procedures a c in Step 4 of Section 4 2 Full meteorology is used instead of the A C and E or F subset used by the hand calculations because SCREEN provides maximum 45 concentrations function of distance and stability classes A C and E or F may not be controlling for all distances The use of
36. d the pkunzip decompression program resident on the hard disk drive The pkunzip program can be obtained via the Support Center for Regulatory Air Models SCRAM Bulletin Board System BBS by accessing the archivers dearchivers option under system utilities on the top menu Insert the SCREEN diskette in floppy drive A and enter the following command at the DOS prompt from drive C either from the root directory or a subdirectory PKUNZIP A SCREEN3 This command will decompress the six files from the SCREEN diskette and place them on the hard disk The hard disk will now contain the executable file of SCREEN called SCREEN3 EXE well as the FORTRAN source files SCREEN3 FOR and MAIN INC an example input file EXAMPLE DAT an associated output file EXAMPLE OUT and this document the SCREEN3 Model User s Guide in WordPerfect 5 1 format SCREEN3 WPF 2 3 Executing the Model The SCREEN model is written as an interactive program for the PC as described earlier Therefore SCREEN is normally executed by simply typing SCREEN from any drive and directory 7 that contains the SCREEN3 EXE file and responding to the prompts provided by the program However a mechanism has been provided to accommodate the fact that for some applications of SCREEN the user might want to perform several runs for the same source changing only one or a few input parameters This mechanism takes advantage of the fact that the Disk Operating System DOS
37. e Enter Choice of Meteorology of Meteorology Enter Title 1 Full Met 1 Full Met 2 Stab 2 Single Stab 3 8ing Wind Speed 3 Sing Stab amp Wind Speed Enter Enter Min and Source Use Use Enter Min and Type V for Max Dist Yes Automated Mex Dist for Volume Source Automated Distances Distances Automated Distance Enter Y Enter Y Distance Array m or N or M Array m No Print Out Print Out Enter Maximum Maximum Emission Rate Concentrations Concentrations g s by Distance by Distance Print Print Out Overall Max Overall Max Concentration Concentration end Distance end Distance Enter Initial User User Enter Terrain Lateral Enter Specified Specified Height Above Enter Dimension of Distance from Distances Distances Stack Base Distance from Source Source Enter Y m Source or No Enter Initial Is Print Out Vertical Distance Summary ef Distance Dimension of from Source psaN Terrain from Source Source gt Heights Used gt Enter Print Out Receptor Maximum Maximum Height Above Concentration Concentration Ground at Specified at Specified m Distance Distance Enter Print Urban Rural Yes Hardcopy Option Results U
38. e exit velocity flow rate option The default choice for this input is stack gas exit velocity which SCREEN will read as free format However if the user precedes the input with the characters VF in columns 1 3 then SCREEN will interpret the input as flow rate in actual cubic feet per minute ACFM Alternatively if the user inputs the characters VM in columns 1 3 then SCREEN will interpret the input as flow rate in m s user can input either upper or lower case characters for VF and VM The flow rate values are then converted to exit velocity in m s for use in the plume rise equations based on the diameter of the stack SCREEN allows for the selection of urban or rural dispersion coefficients The urban dispersion option is selected by entering a U lower or upper case in column 1 while the rural dispersion option is selected by entering an R upper or lower case in column 1 For compatibility with the previous version of the model SCREEN also allows for an input of 1 to select the urban option or a 2 to select the rural option Determination of the applicability of urban or rural dispersion is based upon land use or population density In general if 50 percent or more of an area 3 km around the source satisfies the urban criteria Auer 1978 the site is deemed in an urban setting Of the two methods the land use procedure is considered more definitive For more detailed guidance on land use classification for ur
39. eat release rate These effective Stack parameters are somewhat arbitrary but the resulting buoyancy flux estimate is expected to give reasonable final plume rise estimates for flares However since building downwash estimates depend on transitional momentum plume rise and transitional buoyant plume rise calculations the selection of effective stack parameters could influence the estimates Therefore building downwash estimates should be used with extra caution for flare releases more realistic stack parameters can be determined then the estimate could alternatively be made 15 with the point source option of SCREEN doing so care should be taken to account for the vertical height of the flame in specifying the release height see Section 3 Figure 5 shows an example for a flare release and Figure 6 shows a flow chart of the flare release inputs options and output 2 6 Area Source Example The third source type option in SCREEN is for area sources which is selected by entering A or a for source type The area source algorithm in SCREEN is based on a numerical integration approach and allows for the area source to be approximated by a rectangular area The inputs requested for area sources are as follows Area Source Inputs Emission rate g s m Source release height m Length of larger side of the rectangular area m Length of smaller side of the rectangular area m Receptor height above ground m
40. ect results it will be easier to work with the file if the original input does not contain any errors More importantly since the inputs requested by SCREEN depend on the options selected it is not advisable to edit the SCREEN DAT file and try to change the options selected An experienced user may be able to do this especially with the help of the input flow charts provided later in this section but it may be easier simply to rerun SCREEN with the new options 2 4 Point Source Example When running SCREEN for a point source or for flare releases and area sources discussed below the user is first asked to provide a one line title up to 79 characters that will appear on the output file The user will then be asked to 8 identify the source type and should enter P or p for a point source the model will identify either upper or lower case letters and will repeat the prompt until a valid response is given For a point source the user will be asked to provide the following inputs Point Source Inputs Emission rate g s Stack height m Stack inside diameter m Stack gas exit velocity m s or flow rate ft min or m s Stack gas temperature K Ambient temperature K use default of 293K if not known Receptor height above ground may be used to define flagpole receptors m Urban rural option U urban rural The SCREEN model uses free format to read the numerical input data with the exception of th
41. ed for faster execution the Gt option specifies the data threshold for storing data in a new segment and the FeSCREEN3 EXE option Specifies the name of the executable file SCREEN3 uses the FORTRAN default unit number of 5 five for reading input from the keyboard and 6 six for writing to the screen The unit number for the disk output file SCREEN OUT is set internally to 9 and the unit number for writing inputs to the data file SCREEN DAT is set to 7 These unit numbers are assigned to the variables IRD IPRT IOUT and IDAT respectively and are initialized in BLOCK DATA at the end of the SCREEN3 FOR source file The Microsoft version of SCREEN also uses the GETDAT and GETTIM system routines for retrieving the date and time These routines require the variables to be INTEGER 2 and they may differ on other compilers The following simple change can be made to the SCREEN source file SCREEN3A FOR in order to create a version that will accept a user specified output filename instead of automatically writing to the file SCREEN OUT An ASCII text editor or a wordprocessor that has an ASCII or nondocument mode may be used to edit the source file Delete the letter C from Column 1 on lines 262 to 265 They should read as follows WRITE IPRT 94 WRITE IPRT ENTER FOR OUTPUT FILE READ IRD 95 OUTFIL 95 FORMAT A12 57 With this change if the user specified filename already exists it will be overwritten If d
42. epresent a 24 hour average by multiplying by a factor of 0 4 while the VALLEY 24 hour estimate incorporates the 0 25 factor used in the VALLEY model Calculations continue for each terrain height distance combination entered until a terrain height of zero is entered The user will then have the option to continue with simple terrain calculations or to exit the program should be noted that SCREEN will not consider building downwash effects in either the VALLEY or the simple terrain component of the complex terrain Screening procedure even if the building downwash option is selected SCREEN also uses a receptor height above ground of 0 0m i e no flagpole receptors in the complex terrain option even if a non zero value is entered The original receptor height is saved for later calculations Refer to Section 3 for more details on the complex terrain screening procedure 2 4 3 Simple Elevated or Flat Terrain Option The user is given the option in SCREEN of modeling either simple elevated terrain where terrain heights exceed stack base but are below stack height or simple flat terrain where terrain heights are assumed not to exceed stack base elevation If the user elects not to use the option for simple terrain screening with terrain above stack base then flat terrain is assumed and 11 the terrain height is assigned a value of zero If the simple elevated terrain option is used SCREEN will prompt the user to enter a terrain height
43. esired the OPEN statement on line 267 may also be changed to read as follows OPEN IOUT FILE OUTFIL STATUS NEW ERR 94 With this additional change the program will continue to prompt for the input filename until a filename that doesn t already exist is entered by the user Before recompiling make any other changes that may be necessary for the particular compiler being used It should be noted that without optimization the source file may be too large to compile as a single unit In this case the SCREEN3A FOR and SCREEN3B FOR files may need to be split up into separate modules that can be compiled separately and then linked together The SCREEN model code has also been successfully compiled with the Lahey F77 EM 32 Fortran compiler with the following compile commands F77L3 SCREEN3A FOR NO NW D1LAHEY F77L3 SCREEN3B FOR NO NW where the NO option suppresses the printing of compile options NW suppresses certain warning messages and DILAHEY defines LAHEY for implementing the conditional compile block of Lahey specific statements for retrieving the system date and time for the output file Follow the instructions with the Lahey compiler for linking the model to create an executable file 58 5 REFERENCES Auer Jr A H 1978 Correlation of Land Use and Cover with Meteorological Anomalies Journal of Applied Meteorology 17 5 636 643 Briggs G A 1969 Plume Rise USAEC Critical Review Series TID 25075
44. gation Models EPA 450 4 87 002 U S Environmental Protection Agency Research Triangle Park NC Environmental Protection Agency 1988 Screening Procedures for Estimating the Air Quality Impact of Stationary Sources Draft for Public Comment EPA 450 4 88 010 U S Environmental Protection Agency Research Triangle Park NC 59 Environmental Protection Agency 1995a Screening Procedures for Estimating the Air Quality Impact of Stationary Sources Revised EPA 450 R 92 019 U S Environmental Protection Agency Research Triangle Park NC Environmental Protection Agency 1995b Industrial Source Complex ISC3 Dispersion Model User s Guide EPA 454 B 95 003b U S Environmental Protection Agency Research Triangle Park NC Hosker R P 1984 Flow and Diffusion Near Obstacles Atmospheric Science and Power Production Randerson D ed DOE TIC 27601 U S Department of Energy Washington D C Leahey D M and M J E Davies 1984 Observations of Plume Rise from Sour Gas Flares Atmospheric Environment 18 917 922 Misra P K and S Onlock 1982 Modelling Continuous Fumigation of Nanticoke Generating Station Plume Atmospheric Environment 16 479 482 Pierce T E D B Turner J A Catalano and F V Hale 1982 PTPLU A Single Source Gaussian Dispersion Algorithm User s Guide EPA 600 8 82 014 U S Environmental Protection Agency Research Triangle Park NC Pierce T E 1986 Addendum to PTPLU A Single
45. ge Stab 3 Sing Stab amp Wind Speed 3 6 Stab Wind Speed Print Out Enter Min and Use Use Enter Terrain Print Out Maximum Max Dist for Yes Automated Automated Yes Height Above Maximum Concentrations Automated Distances Distances Stack Base Concentrations by Distance Distance Enter Y Enter by Distance Array N Print Out Overall Max Concentration and Distance Print Out User User Print Out Maximum Enter Yes Specified Specified Enter Maximum Concentration Distance from Distances Distances Distance from Concentration at Specified Source Enter Y Enter Y Source at Specified Distance or N or N Distance No Yes with New Ter Ht Enter Y or N Bldg Make Print Out Print Out Yes Downwash No Fumigation Inversion Cavity Considered Calcs Enter Break up Resuts Y or N Fumigation Conc 8 Dist Make Shoreine Fumi Cak Y Print Out Enter Min Yes Maximum Distance Shoreline from Source Fumigation to Shoreline Con amp Dist STOP Figure 4 Flow Chart of Inputs and Outputs for SCREEN Point Source Page 2 of 2 28 09 07 95 12 00 00 SCREEN3 MODEL RUN VERSION DATED 95250 FLARE RELEASE EXAMPLE SIMPLE TERRAIN INPUTS SOURCE TYPE FLARE
46. gular Area m Enter Receptor Height Above Ground m Enter Urban Rural Option U Urban R Rural Enter Choice ot Meteorology Use Enter Min and Yes Automated Max Dist for Distances Automated Enter 4 Distance or N Array m Wind Speed Enter Wind Print Out Direction Maximum Relative to Concentrations Long Dimension by Distance deg Print Out Overall Max Concentration and Distance U T Specified Enter Distances Distance from Enter Y Source m er N Is Distance from Source gt 0 Print Maximum Concentration at Specified Distance Out Print Out Summary ot Results Print Hardcopy Results Enter Y N Print Hardcopy of Results Figure 8 Flow Chart of Inputs and Outputs for SCREEN Area Source 39 09 07 95 12 00 00 XXX SCREEN3 MODEL RUN VERSION DATED 95250 VOLUME SOURCE EXAMPLE SIMPLE TERRAIN INPUTS SOURCE TYPE VOLUME EMISSION RATE G S 1 00000 SOURCE HEIGHT M 10 0000 INIT LATERAL DIMEN 50 0000 INIT VERTICAL DIMEN 20 0000 RECEPTOR HEIGHT 0000 URBAN RURAL OPTION RURAL BUOY FLUX 000 M 4 S 3 FLUX 000M 4 S 2 FULL METEOROLOGY SCREEN AUTOMATED DISTANCES TERRAIN HEIGHT OF 0 M ABOVE STACK BASE USED FOR F
47. height and width are HR H HC WR 0 6 H 1 1 W and measured from the lee face of the building The length of the recirculation region is calculated using the formula LR 1 8W L H 1 0 0 24W H with the restriction that L H is set equal to 0 3 if L H 0 3 and L H is set equal to 3 0 if L H 3 0 The ground level concentration in the recirculation region is calculated assuming the mass fraction of the plume below HR at the downwind end of the region is captured into the region The calculation assumes a Gaussian distribution of the vertical mass of the plume at that point using the following formula Og Cadet pin The cavity concentration C is then calculated as a fraction of the plume content using the following empirical formula f Q B w A us where f is the mass fraction of the plume captured in the recirculation region B is an empirical constant approximately equal to 16 wy is the stack exit speed A is the stack exit face area u is the upwind wind speed at roof level s is the stretched string distance between the Stack base and the receptor The position of the stack on the roof is taken into consideration ratio is calculated based on the distance of the Stack from a centerline of the building perpendicular to the wind flow for each of two orientations divided by the along wind flow length of the building Below is an example where the along wind flow length is H
48. ions to exercise SCREEN can perform all of the single source short term calculations in the screening procedures document including estimating maximum ground level concentrations and the distance to the maximum Step 4 of Section 4 2 SPD incorporating the effects of building downwash on the maximum concentrations for both the near wake and far wake regions Section 4 5 1 estimating concentrations in the cavity recirculation zone Section 4 5 1 estimating concentrations due to inversion break up and shoreline fumigation Section 4 5 3 and determining plume rise for flare releases Step 1 of Section 4 2 The model can incorporate the effects of simple elevated terrain on maximum concentrations Section 4 2 and can also estimate 24 hour average concentrations due to plume impaction in complex terrain using the VALLEY model 24 hour screening procedure Section 4 5 2 Simple area sources be modeled with SCREEN using a numerical integration approach The SCREEN model can also be used to model the effects of simple volume Sources using a virtual point source procedure The area and volume source algorithms are described in Volume II of the ISC model user s guide EPA 1995b SCREEN model can also calculate the maximum concentration at any number of user specified distances in flat or elevated simple terrain Section 4 3 including distances out to 100km for long range transport Section 4 5 6 1 5 What will SCREEN not do
49. ke a VALLEY 24 hour estimate assuming F or E and 2 5 m s and also estimate the maximum concentration across a full range of meteorological conditions using simple terrain procedures with terrain chopped off at physical stack height and select the higher estimate Calculations continue until a terrain height of zero is entered For the VALLEY model concentration SCREEN will calculate a sector averaged ground level concentration with the plume centerline height h as the larger of 10 0m or the difference between plume height and terrain 52 height The equation used is X 2 032 Q exp s0 5 h o 17 Note that for screening purposes concentrations are not attenuated for terrain heights above plume height The dispersion parameter Oe incorporates the effects of buoyancy induced dispersion BID For the simple terrain calculation SCREEN examines concentrations for the full range of meteorological conditions and selects the highest ground level concentration Plume heights are reduced by the chopped off terrain height for the simple terrain calculation To adjust the concentrations to 24 hour averages the VALLEY screening value is multiplied by 0 25 as done in the VALLEY model and the simple terrain value is multiplied by the 0 4 factor used in Step 5 of Section 4 2 3 9 Non requlatory Options 3 9 1 Brode 2 Mixing Height Option The Brode 2 Mixing Height Brode 1991 option calculates a mixing height that is calcu
50. lated based on the calculated plume height the anemometer height wind speed and a stability dependent factor which is compared to a stability dependent minimum mixing height The algorithm is expressed as ZI MAX ZI 1 0 ZI where ZI is 300m for A 100m for B and 30m for both C and D stabilities and ZI is 0 01 for A 0 02 tor 0 03 for C and 0 04 for D stability Brode found that the results of using this algorithm appear to provide a fairly consistent level of conservatism relative to the ISCST model 3 9 2 Variable Anemometer Height Option The anemometer height is used in adjusting the wind speed to Stack height wind speed for cavity calculations based on the following power law function UO UOTEN AMAX1 10 HS ZREF 0 20 01 UITEN AMAX1 10 HS ZREF 0 20 where UOTEN initial wind speed value set to 20 m s UITEN initial wind speed value set to 1 m s HS stack height ZREF anemometer height 53 UOTEN is adjusted downward speed is adjusted upward in speed in an iterative process until the minimum wind speed UC that will entrain the plume into a building s cavity is found The critical wind speed is then adjusted to the anemometer height using the reverse of the power law above as follows UC10M UC ZREF AMAX1 10 HS9 0 20 where UC10M represents the critical wind speed at anemometer height ZREF The variables HANE and ZREF are used inte
51. m concentrations will usually be less than about 10 percent For elevated sources with relatively large buoyancy the inclusion of BID may be expected to decrease the estimated maximum concentration by as much as 25 percent 1 7 How does SCREEN differ from PTPLU PTMAX and PTDIS The PT series of models have been used in the past to obtain results for certain screening procedures in Volume 10R EPA 1977 The SCREEN model is designed specifically as a computerized implementation of the revised screening procedures and is much more complete than the earlier models as described above SCREEN model also requires less manual postprocessing than the earlier models by listing the maximum concentrations in the output However many of the algorithms in SCREEN are the same as those contained in PTPLU 2 0 Pierce 1986 For the same source parameters and for given meteorological conditions the two models will give comparable results SCREEN also incorporates the option to estimate concentrations at discrete user specified distances which was available with PTDIS but is not included in PTPLU 1 8 What changes have been incorporated into SCREEN The SCREEN3 model dated 95250 includes one major revision to the previous version of SCREEN dated 92245 finite line segment algorithm for modeling area sources has been replaced with a numerical integration algorithm based on the ISCST EPA 1995b model new algorithm allows
52. m Equation 5 2 of Turner 1970 50 X Q 2n u o h 8 26 1 14 where is the emission rate g s and other terms are defined above dispersion parameters and o incorporate the effects of buoyancy induced dispersion If the distance to the maximum fumigation is less than 2000m then SCREEN sets X 0 since for such short distances the fumigation concentration is not likely to exceed the unstable limited mixing concentration estimated by the simple terrain screening procedure 3 7 2 Shoreline Fumigation For rural sources within 3000m of a large body of water maximum shoreline fumigation concentrations can be estimated by SCREEN stable onshore flow is assumed with stability class A8 Az 0 035 K m and stack height wind speed of 2 5 m s Similar to the inversion break up fumigation case the maximum ground level shoreline fumigation concentration is assumed to occur where the top of the stable plume intersects the top of the well mixed thermal internal boundary layer TIBL An evaluation of coastal fumigation models EPA 1987b has shown that the TIBL height as a function of distance inland is well represented in rural areas with relatively flat terrain by an equation of the form h A x 15 where h height of the TIBL m TIBL factor containing physics needed for TIBL parameterization including heat flux x inland distance from shoreline m Studies e g Misra and
53. mple rectangular box Wake effects are included in any calculations made using the automated distance array or discrete distance options described below Cavity calculations are made for two building orientations first with the minimum horizontal building dimension alongwind and second with the maximum horizontal dimension alongwind The cavity calculations are summarized at the end of the distance dependent calculations Refer to Section 3 6 for more details on the building downwash cavity and wake screening procedure 2 4 1 2 Non Regulatory Building Downwash Option A Schulman Scire Building Downwash Cavity option can be selected along with two other non regulatory options by entering the appropriate flag SS on the line containing the source type input The program will later ask for the building height minimum horizontal dimension and maximum horizontal dimension in meters as is done for the regulatory cavity option However for this option only the program will ask for the position of the Source on the building with respect to the two building orientations mentioned in 2 4 1 1 The response will need to be in the form of a ratio of the stack distance from a building centerline drawn perpendicular to the wind over the horizontal dimension of the side of the building which is parallel to the wind The program will show a figure on how to calculate the 10 correct ratio for a particular orientation 2 4 2 Complex Terrain Opti
54. n above stack base within 50 km of the source and exercise the automated distance array option out to 50 km For isolated terrain features a separate calculation can be made using the discrete distance option for the distance to the terrain feature with the terrain height input as the maximum height of the feature above stack base Where terrain heights vary with distance from the source then the SCREEN model can be run on each of several concentric rings using the minimum and maximum distance inputs of the automated distance option to define each ring and using the maximum terrain elevation above Stack base within each ring for terrain height input As noted above the terrain heights are not allowed to decrease with distance in SCREEN If terrain decreasing with distance in all directions 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 but as a first cut it is suggested that ring sizes of about 5 km be used i e 0 5km 5 10km etc The application of SCREEN to evaluating the effects of elevated terrain should be done in consultation with the permitting agency 2 4 4 Choice of Meteorology 12 For simple elevated or flat terrain screening the user will be given the option of selecting f
55. nd when calculating concentrations under limited mixing conditions To account for these reflections the hand calculation screening procedure Procedure a of Step 4 in Section 4 2 SPD increases the calculated maximum concentrations for A stability by a factor ranging from 1 0 to 2 0 The factor is intended to be a conservative estimate of the increase due to limited mixing and may be slightly higher about 5 to 10 percent than the increase obtained from SCREEN using the multiple reflections depending on the source Also SCREEN handles the near neutral high wind speed case Procedure b by examining a range of wind speeds for stability class C and selecting the maximum In contrast the hand calculations are based on the maximum concentration estimated using stability class C with a calculated critical wind speed and a 10 meter wind Speed of 10 m s This difference should result in differences in maximum concentrations of less than about 5 percent for those 3 sources where the near neutral high wind speed case is controlling The SCREEN model results also include the effects of buoyancy induced dispersion BID which are not accounted for by the hand calculations except for fumigation The inclusion of BID in SCREEN may either increase or decrease the estimated concentrations depending on the source and distance For sources with plume heights below the 300 meter limit of the hand calculations the effect of BID on estimated maximu
56. ntal Building Dimension m Make Complex Ter 24 hour Calc Enter Y or N No Yes Print Out Plume Height and Dist to Final Rise m Enter Terrain Helght m and Distance to Terrain m le Terrain Height No Yes Print Complex Terrain 24 hr Concentration Out More SCREEN with Simp Terrain Enter Y or N Yes No Figure 6 Flow Chart of Inputs and Outputs for SCREEN Flare Release Page 1 of 2 33 Enter Choice of Meteorology Enter Choice of Meteorology Full Met 2 Singe Stab 3 Sing Stab amp Wind Speed 3 6 Stab Wind Speed Print Out Enter Min and Use Use Enter Terrain Print Out Maximum Max Dist for Yes Automated Automated Yes Height Above Maximum Concentrations Automated Distances Distances Stack Base Concentrations by Distance Distance Enter Y Enter by Distance Array N Print Out Overall Max Concentration and Distance Print Out User User Print Out Maximum Enter Yes Specified Specified Enter Maximum Concentration Distance from Distances Distances Distance from Concentration at Specified Source Enter Y Enter Y Source at Specified Distance or N
57. of SCREEN for a volume Source and Figure 10 provides a flow chart of inputs options and outputs for volume sources 17 1 SUMMARY OF SUGGESTED PROCEDURES FOR ESTIMATING INITIAL LATERAL DIMENSIONS AND INITIAL VERTICAL DIMENSIONS FOR VOLUME SOURCES za Description of Source Initial Dimension a Initial Lateral Dimensions Single Volume Source length of side divided by 4 3 b Initial Vertical Dimensions o Surface Based Source h 0 O vertical dimension of Source divided by 2 15 Elevated Source h 0 on or building height divided Adjacent to a Building by 2 15 Elevated Source h gt 0 not on o vertical dimension of or Adjacent to a Building source divided by 4 3 2 8 Non requlatory Options On the same source type input line the program allows the input of three additional input N nn n and SS Where nn n represents a numerical anemometer height such as 7 5 meters These input when entered cause the program to use the non regulatory Brode 2 Mixing Height 1991 option N a user Specified anemometer height nn n and or a non regulatory building downwash cavity option Schulman and Scire 1993 55 SCREEN printout While additional input is required for the Schulman Scire Building Downwash Cavity option as was discussed in Section 2 4 1 2 no additional input data are required for the other two options 18 Order of Options in SCREEN Input
58. on The complex terrain option of SCREEN allows the user to estimate impacts for cases where terrain elevations exceed stack height If the user elects this option then SCREEN will calculate and print out a final stable plume height and distance to final rise for the VALLEY model 24 hour screening technique This technique assumes stability class F E for urban and a stack height wind speed of 2 5 m s For complex terrain maximum impacts are expected to occur for plume impaction on the elevated terrain under stable conditions The user is therefore instructed to enter minimum distances and terrain heights for which impaction is likely given the plume height calculated and taking into account complex terrain closer than the distance to final rise If the plume is at or below the terrain height for the distance entered then SCREEN will make a 24 hour concentration estimate using the VALLEY screening technique If the terrain is above stack height but below plume centerline height for the distance entered then SCREEN will make a VALLEY 24 hour estimate assuming E or F and 2 5 m s and also estimate the maximum concentration across a full range of meteorological conditions using simple terrain procedures with terrain chopped off at physical stack height The higher of the two estimates is selected as controlling for that distance and terrain height both estimates are printed out for comparison The simple terrain estimate is adjusted to r
59. pheric Dispersion Estimates Turner 1970 The distance to maximum fumigation is based on an estimate of the time required for the mixing layer to develop from the top of the stack to the top of the plume using Equation 5 5 of Turner 1970 u LC u IL C R A Az h hj h 2 13 where downwind distance to maximum concentration m time required for mixing layer to develop from top of stack to top of plume 6 u wind speed 2 5 m s assumed ambient air density 1205 g m at 20 C specific heat of the air at constant pressure 0 24 cal gK R net rate of sensible heating of an air column by solar radiation about 67 cal m s A Az vertical potential temperature gradient assume 0 035 K m for F stability h height of the top of the plume m h 2o h is the plume centerline height h physical stack height m vertical dispersion parameter incorporating buoyancy induced dispersion m The values of u and A Az are based on assumed conditions of stability class F and stack height wind speed of 2 5 m s for the Stable layer above the inversion The value of h incorporates the effect of buoyancy induced dispersion on o however elevated terrain effects are ignored The equation above is solved by iteration starting from an initial guess of 5 000m The maximum ground level concentration due to inversion break up fumigation X is calculated fro
60. r f to the question on source type the user selects the flare release option This option is similar to the point source described above except for the inputs needed to calculate plume rise The inputs for flare releases are as follows Flare Release Inputs Emission rate g s Flare stack height m Total heat release rate 1 Receptor height above ground m Urban rural option U urban rural The SCREEN model calculates plume rise for flares based on an effective buoyancy flux parameter An ambient temperature of 293K is assumed in this calculation and therefore none is input by the user It is assumed that 55 percent of the total heat is lost due to radiation Plume rise is calculated from the top of the flame assuming that the flame is bent 45 degrees from the vertical SCREEN calculates and prints out the effective release height for the flare SCREEN provides the same options for flares as described earlier for point sources including building downwash complex and or simple terrain fumigation and the automated and or discrete distances The order of these options and the user prompts are the same as described for the point source example While building downwash is included as an option for flare releases it should be noted that SCREEN assumes an effective stack gas exit velocity v of 20 m s and an effective stack gas exit temperature T of 1 273K and calculates an effective Stack diameter based on the h
61. rchangeably 3 9 3 Schulman Scire Building Downwash Cavity Option A non regulatory building downwash cavity algorithm Schulman and Scire 1993 has been added as a non regulatory option This option is based on the diffusing plume approach with fractional capture of the plume by the near wake recirculation cavity Extensive parameterization is used to define a building length scale roof recirculation cavity maximum height of the roof cavity and the length of the downwind recirculation cavity as measured from the lee face of the building A building length scale for flow and diffusion is defined as R BS exp 2 3 BL exp 1 3 where BS is the smaller of the building height and projected width for the minimum side orientation BL is the larger of the building height and projected width for the maximum side orientation The length of the roof recirculation cavity is estimated as LC 0 9 The roof cavity will reattach to the roof if LC lt L where L is the downwind length of the roof The maximum height of the roof cavity is defined as HC 2 0 22 R at x 0 5 R where x is the downwind distance The program uses two algorithms to determine the height and width of the downwind recirculation cavity or near wake If the roof cavity reattaches to the roof the height and width are HR H where H is the building height 54 where is the projected width normal to the wind If the roof cavity does not reattach the
62. rom three choices of meteorology 1 full meteorology all stability classes and wind speeds 2 specifying a single stability class or 3 specifying a single stability class and wind speed Generally the full meteorology option should be selected The other two options were originally included for testing purposes only but may be useful when particular meteorological conditions are of concern Refer to Section 3 for more details on the determination of worst case meteorological conditions by SCREEN 2 4 5 Automated Distance Array Option The automated distance array option of SCREEN gives the user the option of using a pre selected array of 50 distances ranging from 100m out to 50 km Increments of 100m are used out to 3 000m with 500m increments from 3 000m to 10 km 5 km increments from 10 km to 30 km and 10 km increments out to 50 km When using the automated distance array SCREEN prompts the user for a minimum and maximum distance to use which should be input in free format i e separated by a comma or a space SCREEN then calculates the maximum concentration across a range of meteorological conditions for the minimum distance given 1 meter and then for each distance in the array larger than the minimum and less than or equal to the maximum Thus 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 dis
63. s for SCREEN Area Source oW ee u I Re owe Wl de S de up 32 97 SCREEN Volume Source Example 33 10 Flow Chart of Inputs and Outputs for SCREEN Volume Source 2 96 ux OX VES OE i de Sg 224 TABLES Page Summary of Suggested Procedures for Estimating Initial Lateral Dimensions and Initial Vertical Dimensions for Volume Sources 18 Wind Speed and Class Combinations Used 52 the 47 37 SCREEN Model vii H H H 1 INTRODUCTION 1 1 Overview of User s Guide It will be easier to understand this user s guide and the SCREEN model if you are already familiar with the Screening Procedures for Estimating the Air Quality Impact of Stationary Sources EPA 1995a This introduction should answer most of your general questions about what the SCREEN model can and cannot do and explain its relationship to the Screening Procedures Document SPD above Section 2 provides several examples of how to run the SCREEN model and will also help the novice user get started The point source example provides the most detailed description and should be read before the other examples If you are already familiar with personal computers and with the screening procedures you probably will not have much trouble simply running SCREEN and experimenting with it It runs interactively and
64. s will be overwritten and lost Thus if you wish to save results of a particular run then change the name of the output file using the DOS RENAME command e g type REN SCREEN OUT SAMPLE1 OUT or print the file using the option at the end of the program If SCREEN OUT is later printed using the DOS PRINT command the FORTRAN carriage controls will not be observed Instructions are included in Section 4 for simple modifications to the SCREEN code that allow the user to specify an output filename for each run Figure 2 shows an example using the complex terrain screen only Figure 3 shows an example for an urban point source which uses the building downwash option the DWASH column of the output NO indicates that no downwash is included HS means that Huber Snyder downwash is included SS means that Schulman Scire downwash is included and NA means that downwash is not applicable since the downwind distance is less than 3L A blank in the DWASH column means that no calculation was mad for that distance because the concentration was so small 14 Figure 4 presents flow chart of all the inputs and various options of SCREEN for point sources Also illustrated are all of the outputs from SCREEN If a cell on the flow chart does not contain the words Enter or Print out then it is an internal test or process of the program and is included to show the flow of the program 2 5 Flare Release Example By answering F o
65. tal dimension alongwind For screening purposes this is thought to give reasonable bounds on the cavity estimates The first case will maximize the cavity height and therefore minimize the critical wind speed However the A term will also be larger and will tend to reduce concentrations The highest concentration that potentially effects ambient air should be used as the controlling value for the cavity procedure 3 6 2 Wake Region The calculations for the building wake region are based on the ISC model EPA 1995b The wake effects are divided into two regions one referred to as the near wake extending from 3L to 101 L is the lesser of the building height h maximum projected width and the other as the far wake for distances greater than 10L For the SCREEN model the maximum projected width is calculated from the input minimum and maximum 49 horizontal dimensions as 12 W2 remainder of the building wake calculations in SCREEN are based on the ISC user s guide EPA 19955 It should be noted that unlike the cavity calculation the comparison of plume height due to momentum rise at two building heights to wake height to determine if wake effects apply does not include stack tip downwash This is done for consistency with the ISC model 3 7 Fumigation 3 7 1 Inversion Break up Fumigation The inversion break up screening calculations are based on procedures described in the Workbook of Atmos
66. tances less than the site boundary If the automated distance array is used then the SCREEN model will use an iteration routine to determine the maximum value and associated distance to the nearest meter If the minimum and maximum distances entered do not encompass the true maximum concentration then the maximum value calculated by SCREEN may not be the true maximum Therefore 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 and some trial and error may be necessary however the user can input a distance of 50 000m to examine the entire array The iteration routine stops after 50 iterations and prints out a message if the maximum is not found Also since there may be several local maxima in the concentration distribution associated with different wind speeds it is possible that SCREEN will not identify the overall maximum in its iteration This is not likely to be a frequent occurrence but will be more likely for stability classes C and D due to the larger number of wind speeds examined 2 4 6 Discrete Distance Option The discrete distance option of SCREEN allows the user to 13 input specific distances Any number of distances gt 1 meter can be input by the user and the maximum concentration for each distance will be calculated The user will always be given this option whether or not the automated distance
67. the user to model rectangular area sources with aspect ratios length width of up to 10 1 new algorithm also provides estimates of concentration within the area source itself and also includes three non regulatory options Three new non regulatory optional features have been added to this model The first feature is the inclusion of an alternative mixing height algorithm Brode 1991 The alternative mixing height is determined by using the maximum of a predetermined mixing height or a value adjusted slightly higher than the plume height whichever is greater Both the mixing height and adjustment values to the plume height are based on stability class Selection of this algorithm results in 4 concentrations that are generally more conservative than output from the ISCST3 model The second feature allows the optional input of an anemometer height in place of the default height of 10 meters This affects the stack top wind speeds for Choice of Meteorology selections 1 and 2 For Choice of Meteorology selection 3 the user is prompted to entered a 10 meter wind speed which is unaffected by any optionally entered anemometer height The third feature is the inclusion of an alternative building cavity algorithm Schulman and Scire 1993 published concentration results using this algorithm model the sampled wind tunnel test concentrations better than the regulatory algorithm for the range selected The options are activated
68. used in interpreting results as the value of x increases use of A 6 in Equations 15 and 16 may not be conservative in these cases since there will be an increased chance that the plume will be calculated as being below the TIBL height and therefore no fumigation concentration estimated Whereas a smaller value of A could put the plume above the TIBL with a potentially high fumigation concentration Also this Screening procedure considers only TIBLs that begin formation at the shoreline and neglects TIBLs that begin to form offshore 3 8 Complex Terrain 24 hour Screen The SCREEN model also contains the option to calculate maximum 24 hour concentrations for terrain elevations above stack height final plume height and distance to final rise are calculated based on the VALLEY model screening technique Burt 1977 assuming conditions of F stability E for urban and a stack height wind speed of 2 5 m s Stack tip downwash is incorporated in the plume rise calculation The user then inputs a terrain height and a distance m for the nearest terrain feature likely to experience plume impaction taking into account complex terrain closer than the distance to final rise If the plume height is at or below the terrain height for the distance entered then SCREEN will make a 24 hour average concentration estimate using the VALLEY screening technique If the terrain is above stack height but below plume centerline height then SCREEN will ma

Screen3 Model User's Guide - Environmental Protection Agency

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