Short description of model

ISORROPIA and ISORROPIA II are models that calculates the composition and phase state of an ammonia -sulfate -nitrate -chloride -sodium -calcium -potassium -magnesium -water inorganic aerosol in thermodynamic equilibrium with gas phase precursors. ISORROPIA was originally developed at the Division of Marine and Atmospheric Chemistry of the Rosenstiel School of Marine and Atmospheric Science, University of Miami, and ISORROPIA-II at the Schools of Earth & Atmospheric Sciences and Chemical & Biomolecular Engineering at the Georgia Institute of Technology. The objectives were to develop a computationally efficienct and rigorous aerosol thermodynamics module for usage in regional and global aerosol models. The complete theory of ISORROPIA, together with a detailed description of the equations solved, the activity coefficient calculation methods and the computational algorithms used can be found in Nenes et al., 1998a,b and Fountoukis and Nenes, 2007 . The performance and advantages of ISORROPIA over the usage of other thermodynamic equilibrium codes has been assessed in numerous studies (e.g., Nenes et al. 1998b; Ansari and Pandis, 1999ab; Yu et al., 2005). It has been evaluated wth numerous in-situ data sets (e.g., Nowak et al., in press; Yu et al., 2005; Fountoukis et al., 2009).

ISORROPIA (ISORROPIA-II) can solve for two classes of problems:

Forward (or "closed system") problems, in which known quantities are temperature, relative humidity and the total (i.e. gas+aerosol) concentrations of NH3, H2SO4, Na, (Ca, K, Mg), HCl and HNO3. Such computations are needed when the total concentrations of precursors are solved for in a model.

Reverse (or "open system") problems, in which known quantities are temperature, relative humidity and the aerosol phase concentrations of NH3, H2SO4, Na, (Ca, K, Mg), HCl and HNO3. Such computations are needed in detailed models of aerosol dynamics, such as MADM (Pilinis et al.,2000 ).

In both types of problems, the aerosol can be either in a thermodynamically stable state (where salts precipitate once the aqueous phase becomes saturated) or in a metastable state (where the aerosol is composed only of a supersaturated aqueous phase).

The source code of ISORROPIA is written primarily in FORTRAN 77. The only extensions to the ANSI standard implemented were the usage of INCLUDE statements, trailing comments, and variable names with length larger than 6 characters (but not larger than 9). These extensions are supported by the majority of FORTRAN 77 compilers, and are also included in the Fortran 90 standard, so they should not pose any portability problems. The model has extensively been tested on many platforms (DEC Alpha, HP and IBM RISC workstations under UNIX, Intel-based PC’s under MS-DOS and Windows 95) and compilers (both FORTRAN 77 and Fortran 90). The results during these tests were found to be independent of the system used.

Since its original release in 1997 (version 1.0), the code has been widely used in air quality and global aerosol modeling studies. As a result, it is constantly being updated and expanded. It's most recent extension, known as ISORROPIA II, incorporate a larger number of aerosol species (Ca, Mg, K salts) and was developed with support from NOAA. ISORROPIA-II is designed to be a superset of ISORROPIA, and uses the exact same routines as ISORROPIA to compute the equilibrium composition when crustal species are not present (i.e., when concentration of Ca, K, Mg are zero). This means that replacing ISORROPIA with ISORROPIA-II should produce identical results, except for when crustal species are present.

ISORROPIA is slowly being phased out and replaced by ISORROPIA-II. Updates to the source code of ISORROPIA 1.7 will be discontinued June 1, 2010 (although the source code and manual for 1.7 will be available for download), but support will be provided for ISORROPIA-II. Users of ISORROPIA are recommended to download and test ISORROPIA-II at their earliest convenience. Those that choose not to update the source code to ISORROPIA-II will still continue to recieve support (as routines of 1.7 are incorporated in ISORROPIA-II) but will have to manually maintain their copy (starting June 1, 2010).

A code (called HETV) which is based on the algorithms of ISORROPIA for sulfate, nitrate and ammonium aerosol systems has been developed. This code is optimized for running on vectorized architectures.

User support

For questions or to report bugs, please send an e-mail to either Athanasios Nenes ( or Christos Fountoukis ( When reporting bugs, please provide the specific input (i.e. precursor concentrations, T, RH) together with the output generated from the code, the computer platform and compiler options used. If relevant, provide the line of the code where the error was generated.

ISORROPIA mail list

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Download the latest versions of the codes

Notice: By downloading these codes, you agree to abide with these terms of usage. If you do not agree to any of these terms, you may not download the codes.

ISORROPIA (NH3, H2SO4, Na, HCl and HNO3 systems)

- Stand-alone executable ( that runs under Windows 9x/NT/2000/ME/XP (Last updated: May 26, 2009)

- Source code (e-mail to request the password) (Last updated: May 26, 2009)

- ISORROPIA manual (Last updated: May 26, 2009).

ISORROPIA-II (NH3, H2SO4, Na, Ca, K, Mg, HCl and HNO3 systems)

- Stand-alone executable ( that runs under Windows 9x/NT/2000/ME/XP (Last updated: May 26, 2009)

- Source code (e-mail to request the password) (Last updated: May 26, 2009)

- ISORROPIA-II manual (Last updated: May 26, 2009).


The development of the first release of the code (version 1.0) was done with support from the Environmental Protection Agency under grant R-824793010, from the National Science Foundation under grant ATM-9625718, and from the ONR studentship by grant N000149510807.

Versions 1.1 to 1.6 were developed with the contributions of many people. In particular we would like to acknowledge the contributions (in alphabetical order): Asif Ansari, Veronique Bouchet, Prakash Bhave, Bill Hutzel, Kevin Kapaldo, Bonyoung Koo, Sonia Kreidenweis, Paul Makar, Federico San Martini, Chris Nolte, Betty Pun, Armistad Russell, Uma Shankar, Jason West, Douglas Waldron, Ashraf Zakey, Yang Zhang. The feedback and bug reports from many other individuals using the code is greatly appreciated.

Versions 1.7 and 2.0 was developed with support from the National Oceanic and Atmospheric Administration (NOAA) under contract NMRAC000-5-04017. We would also like to acknowledge the contributions of Prakash Bhave and Chris Nolte.

Version 2.1 is maintained by the authors without formal support from funding agencies.


Ansari AS, Pandis SN (1999a) An analysis of four models predicting the partitioning of semivolatile inorganic aerosol components, Aeros.Sci.Tech., 31, 129-153

Ansari AS, Pandis SN (1999b) Prediction of multicomponent inorganic atmospheric aerosol behavior, Atmos.Env., 33, 745-757

Fountoukis, C. and Nenes, A. (2007) ISORROPIA II: A Computationally Efficient Aerosol Thermodynamic Equilibrium Model for K+, Ca2+, Mg2+, NH4+, Na+, SO42-, NO3-, Cl-, H2O Aerosols, Atmos.Chem.Phys., 7, 4639–4659 (Online Publication, Journal reprint) Note

Fountoukis, C., Nenes, A., Sullivan, A., Weber, R., VanReken, T., Fischer, M., Matias, E., Moya, M. Farmer, D., and Cohen, R. (2009) Thermodynamic characterization of Mexico City Aerosol during MILAGRO 2006, Atmos. Chem. Phys., 9, 2141-2156 (Online Publication, Journal reprint) Note

Makar, P.A., Bouchet, V.S., and Nenes, A. (2003) Inorganic Chemistry Calculations using HETV – A Vectorized Solver for the SO4-NO3-NH4 System Based on the ISORROPIA Algorithms, Atmos.Env., 37, 2279-2294, (Journal reprint) Note

Nenes A, Pandis SN, Pilinis C (1998a). ISORROPIA: A new thermodynamic equilibrium model for multiphase multicomponent inorganic aerosols, Aquat.Geoch., 4, 123-152 (Preprint, Journal reprint) Note

Nenes A., Pilinis C., and Pandis S.N. (1998b) Continued Development and Testing of a New Thermodynamic Aerosol Module for Urban and Regional Air Quality Models, Atmos. Env., 33, 1553-1560 (Journal reprint) Note

J.B. Nowak, L.G. Huey, A.G. Russell, J. A. Neuman, D. Orsini, S.J. Sjostedt, A.P. Sullivan, D.J. Tanner, R.J. Weber, A. Nenes, E. Edgerton, and F.C. Fehsenfeld, Analysis of Urban Gas-phase Ammonia Measurements from the 2002 Atlanta Aerosol Nucleation and Real-time Characterization Experiment (ANARChE), J.Geoph.Res., 111, D17308, doi:10.1029/2006JD007113. (Preprint, Journal reprint) Note

Pilinis, C., Capaldo, K.P., Nenes, A., Pandis, S.N. (2000) MADM - A New Multicomponent Aerosol Dynamics Model, Aerosol Sci. Tech., 32(5), 482-502 (Journal reprint) Note

Yu, S.,Dennis, R., Roselle, S., Nenes, A., Walker, J.T., Eder, B., Schere, K., Swall, J. and Robarge, W. (2005) An assessment of the ability of 3-D air quality models with current thermodynamic equilibrium models to predict aerosol NO3-. J.Geoph.Res.,110, D07S13, doi:10.1029/2004JD004718, 2005 (Preprint, Journal reprint) Note

Want more information? Try these links:

Athanasios Nenes Webpage

Spyros Pandis Webpage

Christodoulos Pilinis Webpage

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Last modified: May 26, 2009