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So what exactly is air modeling?

Updated: Apr 13, 2021

Welcome to the Blue Sky Modeling Blog!

Here we’re going to talk all things air modeling, from the latest news/updates to technical details to tales from interesting modeling projects.

To kick off the BSM blog I figured we’d start with a basic concept—what is air dispersion modeling?

I’ll begin with a story from long ago in 1991 when I began my career with the Alabama Department of Environmental Management (a young me is shown to the right). During one of my first days there, the fellow who hired me was teaching me how to run a model. “OK,” he said, “type ‘12’ here, leave that one blank, over there put a ‘6.5’…” After a few minutes of that I finally asked him “Look, I can blindly type in all these numbers you’re dictating to me but what am I actually doing?” He looked at me and said, “I am really glad you asked that—lots of people just type the numbers in but it’s important to understand what you’re actually telling the model to do.”

I’ve carried this lesson with me for my entire career—that a model is a tool that is used to accomplish a goal, and a good modeler understands how to use it in different situations to accomplish that goal.

Think of a saw—at its most basic a saw cuts things. You don’t have to be a construction expert to understand that. However, a skilled woodworker realizes that there are different ways to apply the concept of a saw to solve different problems. A circular saw is great for cutting framing studs, but you wouldn’t want to use it to make a dining room table. A miter saw is great for cutting angles for trim, but you certainly wouldn’t want to use it to finish the leg of a chair. The person who is truly an expert at woodworking understands the different types of saws and how to apply them in different situations to achieve a desired goal.

Modeling is the same way. Sure, lots of people can type source information into the right spots, press “go,” and get some answers—but are they the right answers? Or a better question to ask is are they the best answers?

Just as the woodworker must first understand what they are building before choosing the tools and methods to best get the job done, the modeler must first understand the goals of the project before choosing the tools and methods to best get the job done. For example, the most common use of modeling is to assist with getting a permit—in doing so you want the modeling to be conservative or “worst-case” to clearly prove that the project isn’t going to result in pollutant concentrations that exceed applicable standards. How accurate the results are really doesn’t matter. If a source doesn’t always operate 24 hrs/day but sometimes it does, there may not be a need to take the time to adjust the model to accurately represent that—if your modeling assumes that source operates continuously and your modeling meets the standards, your work is done.

On the other hand, maybe that worst-case approach doesn’t demonstrate compliance. In that case you’ll want to take a step back and look at ways where you can adjust the analysis while still being technically sound. Maybe a source could be represented in the modeling as a buoyant line source instead of a series of point sources. Maybe you can make a case for receptors not being necessary in a certain area, or a different set of meteorological data being appropriate. Maybe you should consider using a different model entirely.

The point of all this is like a saw, a model is a tool. Just as there are different types of saws for different jobs there are different types of models for different tasks. But even after you select the proper model for the job, how you use it is important.

Yes, anybody can pick up a saw and make a table out of some wood. But a skilled woodworker knows the kind of wood to use and the kinds of saws to use to make table they want.

Yes, anybody can pick up a dispersion model and get some answers. But a skilled modeler knows how best to feed the model with information and which model to use to get the answer he or she wants.

Be sure to subscribe for future modeling musings!

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