Screening models

Klamt A 1995. Conductor-like Screening Model for Real Solvent A New Approach to the Quantitativt Calculation of Solvation Phenomena. Journal of Physical Chemistry 99 2224-2235. 

The conductor-like screening model (COSMO) is a continuum method designed to be fast and robust. This method uses a simpler, more approximate equation for the electrostatic interaction between the solvent and solute. Line the SMx methods, it is based on a solvent accessible surface. Because of this, COSMO calculations require less CPU time than PCM calculations and are less likely to fail to converge. COSMO can be used with a variety of semiempirical, ah initio, and DFT methods. There is also some loss of accuracy as a result of this approximation. 

COSMO (conductor-like screening model) a method for including solvation effects in orbital-based calculations... 

Perry, S. G., Paumier, J. O., and Burns, D. J., Evaluation of the EPA Complex Terrain Dispersion Model (CTDMPLUS) with the Lovett Power Plant Data Base, pp 189-192 in "Preprints of Seventh Joint Conference on Application of Air Pollution Meteorology with AWMA," Jan. 14-18,1991, New Orleans, American Meteorological Society, Boston, 1991. Bums, D. ]., Perry, S. G., and Cimorelli, A. ]., An advanced screening model for complex terrain applications, pp. 97-100 in "Preprints of Seventh Joint Conference on Application of Air Pollution Meteorology with AWMA," Jan. 14-18, 1991, New Orleans, American Meteorological Society, Boston, 1991. 

As noted, the SCREEN model is written as an interactive program for the PC. Therefore, SCREEN is normally executed by simply typing SCREEN from any drive and directory 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... 

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, which can then be compared with the EXAMPLE.OUT file provided on the program. 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 the following, the last run will be exactly duplicated ... 

The SCREEN model uses free format to read the numerical input data, with the exception of the 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... 

The sidebar discussion presents the order of regulatory options within the SCREEN model for point sources. 

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 distances 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 50,000 m 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. 

The SCREEN model calculates plume rise for flares based on an effective buoyancy flux parameter. An ambient temperature of 293° K 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. 

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 must determine the initial dimensions of the volume source plume before exercising the SCREEN model volume source. Table 3 provides guidance on determining these inputs. 

The use of the methods of Briggs to estimate plume rise are relied on in the SCREEN model. Stack tip downwash is estimated following Briggs (1973, p.4) for all sources except those employing the Schulman-Scire downwash algorithm. Buoyancy flux for non-flare point sources is calculated from ... 

In addition to SCREENS, you can also download TSCREEN, VISCREEN, and CTSCREEN. TSCREEN is a screening model for determining maximum short-term impact from toxic releases. Click the filename to download the file. 

CTSCREEN is a complex terrain screening model of CTDMPLUS. Click the filename (highlighted in blue) to download the file ... 

Erode, R.W., 1991. A Comparison of SCREEN Model Dispersion Estimates with Estimates From a Refined Dispersion Model. Seventh Joint Conference on Applications of Air Pollution Meteorology with A WMA, 93-96. 

Schulman,L.L. and Scire, J.S., 1993. Building Downwash Screening Modeling for the Downwind Recirculation Cavity. Air and Waste, August, 1122-1127. 

Chapter 5 describes simplified methods of estimating airborne pollutant concentration distributions associated with stationary emission sources. There are sophisticated models available to predict and to assist in evaluating the impact of pollutants on the environment and to sensitive receptors such as populated areas. In this chapter we will explore the basic principles behind dispersion models and then apply a simplified model that has been developed by EPA to analyzing air dispersion problems. There are practice and study problems at the end of this chapter. A screening model for air dispersion impact assessments called SCREEN, developed by USEPA is highlighted in this chapter, and the reader is provided with details on how to download the software and apply it. 

Another method is a series of exhaust dilution equations based on Wilson and Lamb " and a series of earlier papers summarized in ASHRAE. This method is based on wind tunnel tests on simplified buildings and is intended to provide conservative (low dilution) results. Wilson and Lamb compared the model to actual field data collected at a university campus and found that the model did indeed predict dilutions similar to measured worst-case dilutions suitable for a screening model. However, many cases resulted in conservative Linderpredictions of dilutions. ... 

Schulman, L. L., and J.S. Scire. 1993. Building downwash screening model for the downwind recirculation cavity. /. Air and Waste Management Association, vol. 43, p. 1122. 

EPA. 1995. SCREEN Model User s Guide. U.S. Environmental Protection Agency, Washington, D.C. 

PTPLU is a point-source dispersion Gaussian screening model for estimating maximum surface concentrations for one-liour concentrations. 

Stenberg, P., Norinder, U., Luthman, K., Artursson, P. Experimental and computational screening models for the prediction of intestinal drug absorption. 

COSMO-RS conductor-like screening model for realistic solvation... 

In 1995, one of the authors (A.K.) introduced the state of a molecule embedded in a perfect conductor as an alternative reference state, which is almost as clean and simple as the vacuum state. In this state the conductor screens all long-range Coulomb interactions by polarization charges on the molecular interaction surface. Thus, we have a different reference state of noninteracting molecules. This state may be considered as the North Pole of our globe. Due to its computational accessibility by quantum chemical calculations combined with the conductor-like screening model (COSMO) [21] we will denote this as the COSMO state. 

Klamt, A. Conductor-like screening model for real solvents a new approach to the quantitative calculation of solvation phenomena. J. Phys. Chem. 1995, 99, 2224-2235. 

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