Atmospheric Dispersion (Part 2)

Gaussian Plume Model
Included in the long list of assumptions for this equation are as follows:

• Constant emission rate
• No wind sheer in vertical or horizontal
• Infinite plume, independent of plume history
• Diffusion negligible downwind
• The dispersion in crosswind and vertical take Gaussian form about the centerline
• Reflective plume surfaces
• Pollutants remain suspended in air following turbulent atmospheric disturbance

More complex calculations can be done with decaying pollutants and plume rise, however the most applicable solutions are those concerning concentrations downwind. These can all be coupled with air quality analysis techniques to give tangible, low variance, results. The references listed below used Pasquill-Gifford-Turner coefficients for diffusion. The following is the general form of the Gaussian Plume equation,

Averaging Times
As part of analysis, often times it is useful to do a time-average of the plume being modeled. This is particularly the case when size of and concentrations in the plume are of interest for the span of a day, week, season, year, etc.

This figure helps to visualize the impact that time-averaging has on a Gaussian plume curve. 

Limitations of the Model
Gaussian plume does not account for inversion conditions chemical transformation, wet deposition, or inhomogeneous terrain. Modifications can be and have been made which make the approach and application to these equations more objective and flexible.

My dad has monitored the air quality in the Jacksonville metropolitan area for more than two decades. Part of his job is to ensure that local businesses aren't putting out any harmful, or large concentrations of, chemicals into the atmosphere. Specially situated monitoring stations do most of the heavy lifting as far as data collection is concerned. Most of his day is spent keeping tract of the ozone condition.  I'll have to ask him if he uses any of the models that we've learned about in class...


http://dept.ceer.utexas.edu/ceer/che357/PDF/Lectures/gaussian_plume_modeling.pdf