Quick Start Guide

Here we briefly summarise how to do thermodynamic calculations using the E-AIM model. Simple worked examples are given. Other essential information on the site includes:

The project page on which we state the purpose of the E-AIM models, list our published papers, and acknowledge the support of funding agencies.
The model description page explains the physical system being modelled, the liquid and solid phases assumed to be present, and the methods used to calculate thermodynamic properties (activity coefficients) in the liquid phase(s). This page references the papers in the peer-reviewed literature that describe the development of the models.
The help page for the properties of the organic compounds in the system explains in detail each of the thermodynamic properties that the user can enter. This should be read together the model description (see link above) for a full understanding of how the model works.
The published papers that describe the data and theory on which E-AIM is based.

In addition, descriptions of the different types of calculation that can be done with the models are linked to each problem input page.

Contents of this page

1. Benefits of registration.
2. What the model can do.
3. Calculating the equilibrium state of a system containing inorganic compounds and water.
4. Calculating the equilibrium state of a system containing organic compounds, inorganic ions, and water.
5. Browser requirements.

1. User Registration

All parts of the site, and all types of calculation, are open to users who choose not to register. However, people whose studies include organic compounds may wish to save the properties of any compounds that they define for later use. This can be done if they register with the site.

When registered users are logged in they can save organic compound definitions to their own private 'library'. These compounds will be available to them whenever they return in the future.

Registered users are also provided with a library code, which they can distribute to others: this code gives access to compounds in the library that the owner designates as 'public'. This facility enables colleagues and students to use these compounds in their own calculations, but they are not able to change the definitions in the library.

Users can register with the site and login from a link on the Available Compounds page, and from the E-AIM home page.

2. What the Model Can Do

There are three types of calculation that E-AIM can do, and each one has its own input page:

A "simple" calculation in which the user specifies the relative humidity, temperature, and moles of ions and organic components present. The model then determines the equilibrium composition of the aerosol, listing the composition of any liquid phase and also the solids present. Values of the partial pressures of trace gases such as H2SO4 and NH3 that would be in equilibrium with the condensed phase are also presented. It is possible to prevent the formation of selected solids, and so investigate the properties of metastable states.
Comprehensive calculations, in which total amounts of water, ions, organic compounds and trace gases per m³ of atmosphere are equilibrated between vapour, solid and liquid phases. Liquid/solid and liquid/gas equilibria can be turned on or off for individual species. It is also possible to equilibrate the system to the vapour pressure of water over ice.
Aqueous solutions and liquid mixtures. Here the models calculate the thermodynamic properties of an aqueous solution or liquid mixture, whose composition (as mol per kg of water) and temperature are input.

Input pages for each of these types of calculation can be accessed from the main pages of the models. There are also pages for the "batch" input of data (many problems at a time), and parametric calculations in which one quantity is varied across a range.

3. Calculations for Inorganic Systems

First, go to the main calculation page for your selected inorganic model:

Model I: H⁺ - SO4²⁻ - NO3⁻ - Cl⁻ - Br⁻ - H2O (180 to 330 K)

Model II: H⁺ - NH4⁺ - SO4²⁻ - NO3⁻ - H2O (180 to 330 K)

Model III: H⁺ - NH4⁺ - Na⁺ - SO4²⁻ - NO3⁻ - Cl⁻ - H2O (at 298.15 K only)

Model IV: H⁺ - NH4⁺ - Na⁺ - SO4²⁻ - NO3⁻ - Cl⁻ - H2O (≤263 to 330 K, depending on composition)

The only difference between these models is the inorganic ions that are included. The same facilities for organic compounds are available for all models.

Next, choose the input page for the type of problem that you have (these selections are unchanged from the previous version of AIM). For a system containing only inorganic compounds, enter the amounts of species in the boxes provided, select the options you need, and press the 'Run' button to do the calculation. Here is a simple example for a system consisting of HNO3 and water:

Go to the main page of Model I, (there is a link on the E-AIM home page).
Enter "0.5" in the relative humidity field, and "1" in both the hydrogen and nitrate fields.
Click on the "Run" button. The result of this equilibration of 1 mole of HNO3 to 50% relative humidity at 298.15 K is an aqueous solution of 12.94 mol kg^-1 HNO3. The equilibrium pHNO3 above the solution is 0.01563 atm. There are no solids.
Changing the temperature to 240 K and re-running the model yields solid HNO3 · 3H2O. The equilibrium pHNO3 above the solid (for 50% relative humidity) is given as 0.2458E-6 atm. This is calculated from the equilibrium between the solid and vapour phase HNO3 and H2O. As a further example, see what happens if the model is run again with HNO3 · 3H2O formation switched off.

Other calculation pages for Model I (accessed from the links at the top of the page you have just used) allow more comprehensive control of the calculation. For example, they enable you to calculate the properties of aqueous solutions of known composition, and properties of systems over a range of conditions (these are called parametric calculations).

4. Calculations for Mixed Inorganic/Organic Systems

First, go to the calculation page for the inorganic model that includes the ions you are interested in. If your chemical system contains only organic compounds, then go to an input page for either Model I or Model II.

Next, press the 'Manage Compounds' button below the input boxes for the ions. This will take you to the Available Compounds page, where you can select compounds from a small library that is provided (or from your own library if you are a registered user), or create the compounds and define their properties yourself. In this example we will assume that you use the library of existing compounds.

Select each compound that you want to use from the drop-down box and press "Add to system". They will appear on the page, beneath the drop-down box. You can view, and also change, the thermodynamic properties of the compounds by clicking on the "View/Edit" links provided for each one. A "Remove" link is also provided so you can exclude the compound from the chemical system (though it still exists in the library, and can be selected again if necessary).

Press the "Return to calculation" button to go back to the problem input page that you started from. You will find that input boxes for the amounts of each organic compound, and options buttons to control their behviour, are now present on the page.

Fill in the in the input boxes for the amounts of inorganic and organic species present, select the options you require and press "Run" to do the calculation.

If you go to another model or calculation page the same set of organic compounds you have just selected will automatically be present. You can return to the Available Compounds page to change them at any time, using the 'Manage Compounds' button. Here is a simple example for a system consisting of HNO3, glutaric acid, and water:

Go to the main page for Model I. Press the button "Manage Compounds" which can be found just after the input fields for the inorganic ions.
From the drop-down selection box choose "Glutaric acid (fitted equation)" and press the button "Add to system". An entry for glutaric acid should then appear on the page, which means that it will now be included in the chemical system treated by the E-AIM model.
The 6 character short names will be used to identify the acid and its anions (produced by dissociation) in the E-AIM model output.
Return to the Model I input page by pressing the button "Return to calculation". You should find an input box for the amount, in moles, of glutaric acid after those for the inorganic ions. (If you go to the Model I page for "Comprehensive" calculations you will also find buttons that enable the dissociation of the acid in aqueous solution to be switched on or off.)
Now define a similar problem to the one for the inorganic system, but this time at 298.15 K: enter "0.8" in the relative humidity field, "1" in both the hydrogen and nitrate fields, and "1" in the glutaric acid amount field. This defines a system containing 1 mole of HNO3 and 1 mole of glutaric acid at a relative humidity of 0.8 (ie., 80%).
Click the "Run" button. The result is an aqueous solution containing 4.05 mol kg^-1 of HNO3 and glutaric acid, and very low concentrations of the glutarate and hydrogen glutarate ions. This is because the dissociation of the organic acid is suppressed by the H⁺ from the nitric acid.
There are a few important things to note. First, there is no equilibrium gas phase partial pressure of glutaric acid listed. This is not because the acid is non-volatile, but because no Henry's law constant or liquid vapour pressure is present in the database for the acid. A value can easily be entered by returning to the Available Compounds page , clicking the link "View/Edit" for glutaric acid and then entering the appropriate value in the Volatility section of the page.

Second, an equivalent relative humidity of 0.787 has been calculated using the Zdanovskii-Stokes-Robinson relationship, and is given near the top of the results page. This is obtained by taking the calculated amount of liquid water in the system (13.696 moles) and determining what the ZSR-based water activity (and therefore relative humidity) would be, treating the system as containing two solute components: the HNO3 + the very small amounts of glutaric acid anions, and undissociated glutaric acid.

In this example we used a single, water soluble, organic compound which existed only in the aqueous phase. It is possible to specify multiple organic compounds to be included in calculations and, depending on their properties, a hydrophobic phase may also occur in the aerosol. See the model description page for details.

5. Browser Requirements

Security and privacy settings on your browser may restrict your ability to use some features of the E-AIM site:

Both cookies and JavaScript must be enabled on your browser in order to do calculations that include organic compounds. The cookies set by the E-AIM site will expire at the end of your session. Don't worry if you are not sure about this: the site tests to see whether both features are present on pages where they are required.
There are no special browser requirements for doing calculations with systems containing only inorganic compounds, or for viewing data pages.

We have tested the operation of the site using Internet Explorer versions 6 and 7, Firefox v2.0, Opera v8 and Safari (Windows beta test version). The site was developed using Firefox.