Which air dispersion model to use

EPA advocates CALPUFF for applications involving longer plume transport, typically 50 km or greater. Consequently, using CALPUFF for EPA regulatory applications for shorter distances may require appropriate examination by the authorities, although CALPUFF has been strongly favored for general applications lately. If you look back at the April 2000 EPA Guideline on Air Quality Models, it says that CALPUFF can also be used in special cases, including complicated stack emissions. The appropriate regulatory affair professionals will look at these on a case-by-case basis and help the regulatory and compliance consultants decide which is best for the situation.

CALPUFF, Aermod or ISC?

This can include domain size and potential for space- and time-varying three-dimensional fields of flow influenced by complex terrain, nonuniform distribution of land use and coastal effects. Additionally, calm or low wind speeds with variable directions may characterize the flows.

For cases which include a high degree of the three-dimensional flow changeability near boundary limits (either upslope or downslope or along winding river valleys) the steady-state assumption might not be very good beyond the limits of even a few thousand metres. Here, the CALPUFF air dispersion model would be far more accurate.

There's one more thing to take into account: when deciding which model is best for each situation, ask whether three-dimensional or temporal distribution of air contaminants matters. This question becomes valid when using the air dispersion model to evaluate risk or when results are to be used for the study of criteria air contaminants where only the peak concentration is important, independent of time or space.

Again, CALPUFF has received stronger support in later years, with the use of some steady-state air dispersion model software, such as ISC, being phased out completely in many jurisdictions.

The modelling software is available for free at this US government webpage: http://www.epa.gov/scram001/dispersion_prefrec.htm - and it is very complicated to learn. Manufacturers and design engineering firms often use atmospheric consultants to work with these tools. They understand the problems and find efficient solutions to avoid harm to the environment.

Need help with this? Try the services of a good air quality and emissions firm for your situation. Call Barry at Calvin Consulting at 403-547-7557 or email - info @ calvinconsulting.ca (remove spaces).

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