Air Quality Models: Architecture

By way of example, we conducted a somewhat unscientific survey. From the Support Center for Regulatory Air Models (SCRAM) web page, we looked at the seven air quality regulatory models that are considered as being "preferred" by the Environmental Protection Agency. The table below shows these models, with a brief description, a checkmark if they can be run on a desktop PC (i.e., are "PC-executable"), and the type of source code the program was programmed in originally:

Model Name	Model Description	PC executable?	Source code language
BLP (Bouyant Line Plume )	a Gaussian plume dispersion model designed to handle unique modeling problems associated with aluminum reduction plants, and other industrial sources where plume rise and downwash effects from stationary line sources are important.		FORTRAN
CALINE3	a steady-state Gaussian dispersion model designed to determine air pollution concentrations at receptor locations downwind of "at-grade," "fill," "bridge," and "cut section" highways located in relatively uncomplicated terrain.		FORTRAN
CDM2 (Climatological Dispersion Model)	a climatological steady-state Gaussian plume model for determining long-term (seasonal or annual) arithmetic average pollutant concentrations at any ground-level receptor in an urban area.		FORTRAN
CTDMPLUS (Complex Terrain Dispersion Model Plus Algorithms for Unstable Situations)	a refined point source gaussian air quality model for use in all stability conditions for complex terrain. The model contains, in its entirety, the technology of CTDM for stable and neutral conditions.		FORTRAN
ISC3 (Industrial Source Complex Model)	a steady-state Gaussian plume model which can be used to assess pollutant concentrations from a wide variety of sources associated with an industrial complex. This model can account for the following: settling and dry deposition of particles; downwash; point, area, line, and volume sources; plume rise as a function of downwind distance; separation of point sources; and limited terrain adjustment. ISC3 operates in both long-term and short-term modes.		FORTRAN
OCD (Offshore and Coastal Dispersion Model)	a straight line Gaussian model developed to determine the impact of offshore emissions from point, area or line sources on the air quality of coastal regions. OCD incorporates overwater plume transport and dispersion as well as changes that occur as the plume crosses the shoreline. Hourly meteorological data are needed from both offshore and onshore locations.		FORTRAN
RAM (Gaussian-Plume Multiple Source Air Quality Algorithm)	a steady-state Gaussian plume model for estimating concentrations of relatively stable pollutants, for averaging times from an hour to a day, from point and area sources in a rural or urban setting. Level terrain is assumed.		FORTRAN
UAM-IV (Urban Airshed Model IV)	an urban scale, three dimensional, grid type numerical simulation model. The model incorporates a condensed photochemical kinetics mechanism for urban atmospheres. UAM-IV is designed for computing ozone (O3) concentrations under short-term, episodic conditions lasting one or two days resulting from emissions of oxides of nitrogen (NOx), volatile organic compounds (VOC), and carbon monoxide (CO). The model treats VOC emissions as their carbon-bond surrogates.		FORTRAN

While all of these codes are currently available as PC-executables, there is clearly a "price" to pay by doing so. The following table, extracted from a paper on regional air quality modeling by Khanh T. Tran and Fabrice Cuq, shows a benchmark comparision table for running the Urban Airshed Model (UAM) on various machines, beginning with a desktop PC and moving down to a high-performance computer:

The graph at the right (click to see full-sized) shows this data visually. It should be much more apparent from this bar graph that, while it is possible to run "larger" models such as the Urban Airshed Model on desktop platforms, that some serious consideration needs to be undertaken by the air quality modeler about the effective use of time and resources.