The Extended Aerosol Inorganics Model Project

The purpose of this project is to provide reference thermodynamic models for gas/liquid/solid equilibrium calculations. The models are mainly for use in aerosol science research and teaching - particularly in air quality and climate science - but also for scientists and students with an interest in solution thermodynamics generally. Many of the data used to develop the model are tabulated on this site. See the model description for details of the physico-chemical system treated and the options available to users.

The Models

The phase equilibrium models of aerosol systems made available on this web site can be used to calculate the equilibrium state of chemical systems containing mixtures of organic compounds, water, and the ions H+, NH4+, Na+, SO42−, NO3, Cl, and Br. There is a small library of organic compounds with pre-assigned thermodynamic properties, which users can vary, if required. Users can also define their own organic compounds, and specify values of quantities such as the solubility product, Henry's law constant or vapour pressure, and activity coefficient model.

The models enable the distribution of water and the other components to be calculated between liquid, solid and vapour phases for ambient conditions (temperature, relative humidity) specified by the user. Up to two liquid phases can exist, one of which is aqueous and the other hydrophobic (see the model description for details). The models are applicable to bulk solutions as well as aerosols, and the chemical equilibrium problems that the model solves can be specified in a variety of ways to accommodate different needs.

The model can be used for bulk solution calculations in which species concentrations are input. This site includes a tutorial section, to help users to learn about how the models work, and basic thermodynamic principles.

Versions of the models that use file-based data input also exist. These run as normal programs, from the command line, on Windows PCs. These executable codes can be made available for special projects on application to the authors.

Click this link for a summary list of the published papers describing the model, and its development.


The chemical thermodynamic treatment of the inorganic systems in the E-AIM models was developed with support from the Natural Environment Research Council of the U.K. (NERC). We are also grateful to NATO and the British Council for small grants that contributed to this work, and resulted in the first web-based version of the Aerosol Inorganics Model in 1998.

Additions to the site, and the exploration of various ways of including organic compounds in the model were carried out with support from the U. S. Environmental Protection Agency (EPA), and in collaboration with EPA staff scientists in Research Triangle Park, North Carolina (see the note below).

The inclusion of organic compounds in the model code, its extension to a wider range of inorganic compounds, and the creation of the E-AIM web site are supported by a knowledge transfer grant from NERC (our partner organisation is the U.K. Met Office), by the European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI), and by a grant from the National Oceanographic and Atmospheric Administration (NOAA). The use of E-AIM in the development of atmospheric models is supported by the Atmospheric Science Program of the U.S. Department of Energy. The tabulations of thermodynamic data presented on the web site were compiled with the support of the ACCENT network (Atmospheric Composition Change, the European Network of Excellence). Work on the inclusion of amines in the model, and a review of amines detected in the atmosphere, has been supported by the Electric Power Research Institute (EPRI).

We would also like to acknowledge our collaborations, over several years, with John Seinfeld (at the California Institute of Technology) and Mike Kleeman (University of California at Davis). Both of these collaborations have contributed substantially to the project.

Note: the work has not been subject to the U.S. EPA’s peer and policy review, and does not necessarily reflect the views of the agency. No official endorsement should be inferred.