Sub-module 3A, page 11
The equilibrium model
Mackay's Level I is the first model for this course. You will have to find the web site, register, and download the model. It will be installed on your machine. The initial download is a zipped exe program which is about 3 megs. After you download that, you double click it and it will install itself in your programs file. If you are on a university computer where you cannot save programs, you should probably have thumb drive then download to that drive and install the program there. So here is the site you want Level I model. You will see a number of links, but go the bottom of that page and click on "Register to Download Level I" then type in your name, etc. and you will eventually get a file downloaded. When you get it installed, you want to come back to this page, minimize it, then start the Level I program, minimize it, and work between this page and the program. I found the link to start the program on my Start Menu.
The program will determine equilibrium for chemicals in the environment. It provides a default environment for a large area that contain air, soil, water, aerosol, sediment and aquatic life. It will answer the question, where does the chemical go? Now if the program tells us that at equilibrium all the chemical will be in the air, we would not be surprised to not find any of the chemical some time after a spill. If it tells us the chemical will be in the sediment, that is where we should sample. The program says nothing about how fast equilibrium is achieved.
After you install the program and start it, you will see the main screen. You should first click on the help button to the right. That has a pretty good description of the program, which you should read. To do a simulation, click on the simulation ID button and name your data, then the chemical button. Here you can select the chemical you will be simulating. As you click on chemicals, note how the properties change. You will click on benzene when you are ready. (You could also add a chemical that is not on the list, if you knew some of its properties.) For the environment, you will see that the default is a very large environment. For starters, I wanted to show you an environment that was just air, water and fish. You must put a small number in each volume, it can't handle a zero volume. Here are the volume numbers I put in for benzene:
I left the Organic Carbon, Densities, and Lipid as defaults.
Finally I put in 1 kg for the emissions.
Here is the output in the Diagram mode.
It tells me that about 4% of the benzene is in the fish, 57% in the water, and 38% in the air. (The program uses the symbol "E" for exponent to the base 10, i.e., "1E +3" is one thousand and 5E-3 is 0.005.) Now this is only equilibrium if the 300 m^3 of air was somehow trapped over the water. The very large default numbers that come up when you open the program indicate a large air shed, perhaps over a city. If it was not windy, perhaps this would be a good equilibrium model. Once you get the program up and running and get a diagram similar to what I got, you will run the program some more. If you keep it running, you need only change the parameters you want to. For the first homework, you will go back to the chemical page and change the chemical from benzene to formaldehyde. Note how the percentages change. Where is most of the formaldehyde? [HW problem 7] Now try it again with 2,3,7,8-TCDD, an relatively insoluble chemical (this is the "dioxin" that the newspapers like to mention). Where is all the dioxin? [HW problem 8]
This is the end of Sub-module 3A.