Air Modelling

by Shoeb
(Dhaka, Bangladesh)

Air dispersion model sketch

Air dispersion model sketch

Q: I need help with air modelling. I want to model air pollution at a point surrounded by several stacks. What will I do and how? Please help.....

Barry's Response - Shoeb:

You can download a model called ISC3 or ISC3prime from There's a simplified version called SCREEN3.

Although SCREEN3 is old and no longer recognized for official purposes, I still like it for quick assessments when helping plant engineers in early design stages. It's great for students, new users, and people who don't have a lot of expensive data. It's fun and you'll learn the basics.

SCREEN3 estimates air pollution concentrations downwind of a point source like a chimney. Including new or modified sources that need permits, it helps evaluate air quality impacts.

A Gaussian dispersion model is used in SCREEN3 to estimate air pollution concentrations at receptors downwind of the source. Weather conditions, source characteristics, and topography all go into predicting pollutants' dispersion in the atmosphere. It's convenient because it uses theoretical weather data instead of hourly weather data.

SCREEN3 is usually used in the early stages of an air quality assessment to estimate potential impacts. If you need a more detailed analysis, you can use AERMOD.

SCREEN3 is free, and the EPA provides technical support. Users can also input data and interpret results using software tools and resources.

Downwash happens when a building causes a localized increase in pollutant concentrations on its downwind side. It happens when air is forced over a building, creating a low pressure area behind it. Learn how to include the results of the BPIP and BPIPprm programs from this same site if there are buildings near your stack.

Building Downwash

Put your stacks and points of interest (receptors) where they belong. A meteorological data set is needed for higher-level models like AERMOD and CALPUFF. It should be for the stack area.

Dispersion Modeling for Regulatory Purposes - AERMOD and CALPUFF estimate air pollution from industrial facilities, power plants, and transportation. Several factors can affect the cost and time for having a project like this completed, including the complexity of the input data and the size of the study area. Some general observations:

- AERMOD is generally faster and cheaper than CALPUFF because it uses a simpler modeling approach. Aermod is a Gaussian dispersion model based on emissions rates, stack heights, and weather. CALPUFF usually takes less time to set up and run.

- In contrast, CALPUFF is a Lagrangian dispersion model that can handle more complex terrain and meteorological conditions, so it's better for studies with large study areas or complicated terrain. Due to its complexity, CALPUFF takes longer to set up and run than AERMOD.

- Both models require expertise to set up and run, and the input data has to be accurate and current. Depending on how complex the study area is, costs can also vary.

While AERMOD is generally faster and cheaper than CALPUFF, the choice depends on your specific study needs and study area complexity. You can download one from my region's government if you need an example. See and select one. The standard in most jurisdictions since 2010 or so has become AERMOD and/or CALPUFF, for considerably more sophisticated air modelling.

Have fun with this.

Professional Air Quality Dispersion Modelling - In the event that you require these results, but the air modelling becomes too complex for you to undertake, please email for further assistance.

Search this site for more information now.

Comments for Air Modelling

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by: kapol

I think you have got the exact answer for you doubts and the question that you have asked was very relevant according to the circumstances. I didn't know much regarding air modeling, but after visiting this blog I think I have got some important points.

Barry's Response - Thanks K, glad I could help.

by: debasish

please guide me how i will prepare a model for air pollution for a mines. i have taken 10 samples with in 10 kms, it is ahilly mining with a predominant wind direction north east .

Barry's Response - Go to the US government SCRAM site and download SCREEN3 for air pollution modeling:

Assume the mine opening is a smoke stack with zero height, its actual diameter and room temperature. See if you can guess at an emission rate for the stuff you are concerned about (such as dust, coded as PM). Play with it a while and see what you get.

Air modelling
by: Anonymous

It a shame that air modeling wasn't more used throughout the history as acid rain was result of lack of it. good answer barry!

Barry's Response - Seems to be getting more well-known these days.

good resources
by: Anonymous

I think you answered her question and provided her with some good links. It is a very interesting question and I was interested to read your answer.

Hope the project goes well!

Barry's Response - I try to help when I can.

Will it work?
by: Anonymous

The design did not look attractive and convincing at the first impression.However hope you get some information soon.

Barry's Response - This is an old website. The original design (for which some elements are still in use) was from March 2003.

by: Steve Dave

My initial impression wasn't a good one. The first thing I saw was what looked to be an MSPaint drawing. Then I noticed the strange pattern on the banner. Then the poor quality of the buttons on the left. The poorly-placed Google Ads distracted from the text, as well. It all immediately drained any interest I might have in the website. I am far from motivated to browse the rest of the site. If I were, however, to search the site, I would hope that the other pages, if not of a better quality, were concise and well-laid out to get across what they needed to before my interest further waned.

Barry's Response - Some of us are scientists, some are web-designers. We all have our capabilities.

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