ELSEVIER Environmental So]iware 9 (1994) 61 66 © 1994 Elsevier Science Limited Printed in Great Britain. All rights reserved 0266-9838/94/$7.00 On local finite element refinements in multiscale air quality modeling Mehmet T. Odman MCNC, North Carolina Supercomputing Center, Research Triangle Park, North Carolina 27709-2889 USA & Armistead G. Russell Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA (Received 5 June 1992; revised version received 30 April 1993: accepted 28 July 1993) Abstract- Variable resolution is a highly desirable property in air quality models, especially in regional applications. Resolution can be increased in dense source regions by using finite element refinements. Here, the important principles that must be obeyed at refinement boundaries are discussed. Mass conservation is achieved by making the element basis functions continuous. Constraint relations that assure continuity for various refinement ratios are described. A second issue is to keep the refinement boundaries free of noise. Since coarse and fine elements act like different media, aliasing errors usually lead to noise waves. A non-linear filter is used to remove some of this noise. Tests are conducted with different refinement ratios to see the effect of increased resolution on accuracy. In general, refinements increase accuracy by reducing diffusion errors. The peak concentrations are overpredicted during the transition from the fine to the coarse grid. These overpredictions are smaller when the refinements are gradual. Key Words -- Finite element refinements, multiscale modeling, variable resolution. Software Availability Name o(the software: Urban and Regional Multiscale (URM) model Brief dega-iption; URM is a photochemical air quality model for use in urban and regional modeling. It allows variable resolution both in the horizontal and vertical domains. The LCC mechanism is used to describe the chemistry. Dgvelotx~Contact Addresses; Armistead G. Russell, Department of Mechanical Engineering, Carnegie-Mellon University, Pittsburgh, Pennsylvania, 15213 U.S.A. Phone: (412) 268-3614 Fax: (412) 268-3348 E-Mail: russeU @pollution.me.cmu.edu Melimet T. Odman, North Carolina Supercomputing Center, MCNC, Research Triangle Park, North Carolina, 27709- 2889, U.S.A. Phone: (919) 248-9235 E-Mail: odman @ncse.org Year first available: I:Iallaalr,,glaa~gk Ikaglam.L~amlagg Fax: (919) 248-9245 1992 32 Mbytes ROM, 512 Mbytes I/O Disk FORTRAN and C 512 Kbytes 61