United States Environmental Protection Agency Atmospheric Sciences Research Laboratory Research Triangle Park NC 27711 Research and Development EPA/600/S8-85/005 Apr. 1985 v>EPA Project Summary An Interim User's Manual for the Advanced Scavenging Module: Version 1.2 J. M. Hales This report provides a user's manual for Version 1.2 of the Advanced Scavenging Module (ASM). It is an in- terim code and is intended primarily for coordinating development of the module with that of the evolving NCAR Regional Acid Deposition Model (RADM). The ASM is currently in evolu- tionary stages; the general framework provided by Version 1.2 is sufficiently well-established to provide the basis for future versions. The code supplied with this manual is a complete, opera- tional system, and was tested. The ASM is activated by two types of subroutine calls from the host code. Upon advancing to some ground-level position (x,y) on the host's numerical computation grid, the ASM is interrogated (using the first subroutine call) to produce the vertical distributions of storm features above that point. Following this, scavenging computations are per- formed repeatedly for each vertical grid position, using the second subroutine call. The primary outputs from these secondary ASM interroga- tions are the transformation rates associated with the physical and chemical components of the scaveng- ing process. These rates are returned to the host code and incorporated with its normal numerical integration procedure. This Project Summary was developed by EPA's Atmospheric Sciences Research Laboratory, Research Triangle Park, NC, to an- nounce key findings of the research project that fs fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction The Advanced Scavenging Module (ASM) is a conceptual framework and computer code for calculating the precipitation scavenging of reactive and nonreactive air pollutants. The module is intended to be used in conjunction with a regional, Eulerian "host" code, which ap- proximates numerically the appropriate equations of conservation and inter- rogates the ASM for needed input regard- ing wet-chemistry and scavenging proc- esses. The ASM can be considered an ad- vancement over its regional predecessors at this point in time, because it is struc- tured to allow a comparatively versatile depiction of individual physicochemical processes within the composite scaveng- ing sequence. This in turn presents the possibility of more accurate source- receptor analysis, and the fruitful in- vestigation of individual chemical con- tributions, nonlinear effects, and associated control strategies. The ASM is being prepared primarily for the National Center for Atmospheric Research (NCAR) Regional Acid Deposition Model (RADM) and an enhanced version of the existing STEM II code, but is sufficiently versatile to be incorporated with a number of addi- tional Eulerian models as well. This version of the module is not sub- mitted as a product that is ready for routine incorporation in a finalized regional model. It is intended, rather, to provide a systematic definition of information-exchange requirements, for ------- the purpose of helping to coordinate development in the overall regional model- ing effort. The Version 1.2 Scavenging Module described in this report takes the form of an executable system of subroutines, which may be interrogated by host codes for development and shake-down purposes. Major Features The two coordination points are par- ticularly important in this regard. The first of these is the development of the host- codes themselves, which must have a number of interactive linkages with the Scavenging Module. The second co- ordination point is with those individuals who are creating the wet-chemical con- version parameterizations for the RADM. In its present state the Scavenging Module provides a convenient substrate for interweaving these parameterizations with cloud-physics processes and gaseous-phase chemistry. Individuals working on both of these efforts should be totally aware of the protocols established in the Scavenging Module, so that a smooth coordination of these linkages will occur. In this context it should be noted that while many internal features of the Scavenging Module are not complete, the framework and information-exchange scheme is in a rather high state of development. Because of this, coordination with other modules and with the host codes can occur at this point with minimum fear of future back- tracking. The Advanced Scavenging Module bears a direct relationship with the evolv- ing reactive storm models in the PLUVIUS series, and many of the procedures and parameterizations employed by the Module are directly traceable to those used in the PLUVIUS codes. Two primary differences exist. The first of these is that the Module is subservient to the host code and is designed to work interactively with a number of outside modules, whereas the PLUVIUS models deal with the total system of conservation equa- tions. The second difference is that PLUVIUS codes generate storm systems on the basis of first principles, whereas the Scavenging Module synthesizes the storms on the basis of empirical formulae and look-up tables. This feature is ap- propriate to the Module for two major reasons: first, it allows a very rapid and computationally efficient generation of essential properties; and second, it pro- vides a convenient means for creating spatially- and temporally-averaged storm features. This is particularly important for the target models, because of temporal and spatial grid-mesh properties. Module Operation The ASM operates in two distinct modes, which may be termed the "storm- generation" and "scavenging" modes. Activation of these modes is controlled via a subroutine argument (MFUNCT), and a number of internal bypass options are available, depending on specific com- putations required by the particular host code in use. In storm-generation mode, the ASM creates vertical profiles of key storm parameters above some chosen position x,y at the surface. These parameters in- clude quantities of the condensed-water media and their associated interconversion rates, as well as a number of auxiliary variables (such as actinic flux) required for reactive scavenging calculations. Condensed-water media for this particular version of the ASM have been lumped in- to the three following categories: • cloud water, • rain, • snow. Vertical profiles of these condensed- water classes are estimated using em- pirical relationships. ASM Version 1.2 employs polynomial fitting functions for this purpose, in conjunction with the following "predictor variables," which must be supplied by the host code: sur- face precipitation rate, surface elevation, surface temperature, storm-type index, cloud-cover index, and cloud base eleva- tion. Cloud interconversion processes of potential importance to the scavenging process include: • cloud autoconversion to rain, • accretion of cloud water by rain, • riming of cloud water by snow, • deposition of water vapor to snow surfaces, • freezing of liquid water, • melting of snow, and • evaporation of condensed water. Transport processes included by the storm environment include: • vertical fall velocities of snow and rain, and • dispersion of snow and rain arising from differential settling of different sizes of hydrometeors. All of these properties are computed by ASM in storm-generation mode. The code is modularized to accommodate pro- gressive improvements in characteriza- tions of these features, and the present Version 1.2 employs the rather simple ex- pressions utilized by the PLUVIUS MOD 5.0 storm code. Since these expressions are described in the PLUVIUS User's Manual, they are not discussed at length in this report. The Version 1.2 described in this report has been written in standard FORTRAN 77 code and, other than for architectural features, has not been prepared for vec- torization on an array-processor. In par- ticular, many of the innermost loops con- tain conditional statements, which will prevent direct vectorization. This choice was made with Version 1.2 because the primary objective of this version is to coordinate development and illustrate in- formation exchange, and inclusion of the conditional statements results in a much more easy-to-follow text. A vectorized replica of Version 1.2 will be prepared for initial blending with the RADM on the NCAR Cray array processor. Upgraded versions of the Advanced Scavenging Module will become available periodically during the next two years. Conclusion Version 1.2 of the ASM should be con- sidered as a partial guide for host-code development and as a form for the im- plementation of wet chemical reaction schemes. The potential user is encour- aged to familiarize himself with the ASM by reproducing the example in the report, and progressively augmenting it as desired. While the ASM's subroutines will undergo extensive development in the future, the framework of the module is essentially at a final stage. Thus, it should be relatively easy to incorporate higher versions into existing host codes, once they are formatted to interact with Ver- sion 1.2. Several new and improved ver- sions are anticipated during the coming year. ------- J. M. Hales is with Battelle Northwest Laboratory, Richland, WA 99352. Jack L. Durham is the EPA Project Officer (see below). The complete report, entitled "An Interim User's Manual for the Advanced Scavenging Module: Version 1.2," Order No. PB85 173 9Q4/AS; Cost: $10.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield. VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Atmospheric Sciences Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 U.S. GOVERNMENT PRINTING OFFICE' 1985-559-016/27030 O.S.aPF'CiALL'AV United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 MAY 15-85 j ,";;.Aiepd 1 jSf. SiOCi & FEES W """ • / B VFTfwRS PERMirNo GT-3& i_ -i u r o ^ i I ' _ Official Business Penalty for Private Use $300 0000329 PS ------- |