Spreading in new directions
During the early development of air dispersion modeling, scientists created several basic models to predict the transport of air contaminants emitted from sources. Such models served an important function in assessing individuals' exposure to hazardous air pollutants (HAPs). The analyses involved the use of various mathematical formulas to determine the rise of a discharge plume after its release from an industrial stack or other source and the dilution of the pollutant concentration as it traveled downwind.
Yet, like strong shifting winds, the pressure of changing environmental laws is currently pushing the application of air dispersion modeling into many different areas. An increased understanding of the complex nature of HAPs' release and movement is also driving the rapid expansion of model types.
Environmental professionals are now using dozens of different computerized models. The selection of the correct model for a specific situation depends on many factors, including the acceptability of the model by environmental scientists and governmental regulators; the estimate's required precision; the input data's availability; and the user's proficiency in utilizing the model.
The U.S. Environmental Protection Agency (EPA) maintains a Web site at www.epa.gov/scram001/index.htm, a source of information on air quality models that support regulatory programs mandated by the Clean Air Act. Documentation and guidance for these modeling software programs are major features of this Web site.
To inform environmental professionals of recent advances in modeling, EPA plans to hold the 7th Conference on Air Quality Modeling in July in Washington, D.C. EPA will announce the conference's exact date in the Federal Register at least 30 days in advance. For more information about this conference, contact EPA's Dennis Atkinson at (919) 541-0518.
As part of the conference, EPA will solicit attendees' comments on the agency's proposal to add three new modeling techniques to Appendix W of 40 Code of Federal Regulations (CFR) Part 51. One of the new models under consideration, CALPUFF, is a multi-layer, multispecies nonsteady-state puff dispersion model that simulates the effects of time- and space-varying meteorological conditions on pollutant transport, transformation and removal. This model can be applied on scales of tens of meters to hundreds of kilometers.
Another new model EPA is evaluating is the latest version of the Industrial Source Complex Short Term Model (ISCST3). Referred to as ISC-PRIME, this test model incorporates plume rise model enhancements (PRIME), which is a set of algorithms evaluated as the next generation building downwash model.
Finally, the last model under review is the fruit of a collaboration between two groups. The American Meteorological Society and the EPA Regulatory Model Improvement Committee recently formed the joint committee, AERMIC, designed to introduce state-of-the art modeling concepts into EPA's air quality models. AERMIC's focus is on a new platform for regulatory steady-state plume modeling. The modeling system has three components: AERMOD - the air dispersion model; AERMET - the meteorological data preprocessor; and AERMAP - the terrain data preprocessor.
IMAGE COURTESY OF BREEZE GRAPHICS®, TRINITY CONSULTANTS
This article originally appeared in the 06/01/1999 issue of Environmental Protection.