ISORROPIA II
Overview
The ISORROPIA II package performs aerosol thermodynamical equilibrium. It partitions nitrate (HNO3 and NIT) and ammonia (NH3 and NH4) between the gas and aerosol phases. Inputs to the partitioning routine include temperature and RH. ISORROPIA II has significant benefits over previous implementations of ISORROPIA, especially for partitioning of nitrate at low RH.
Authors and collaborators:
- Thanos Nenes (Georgia Tech) -- Principal Investigator
- Havala O. T. Pye (Caltech)
Implementation notes
As of Jan 27, 2010, ISORROPIA II is currently being implemented into GEOS-Chem v8-02-05 (version in testing).
Code structure
The main-level Code directory has now been divided into several subdirectories:
GeosCore/ GEOS-Chem "core" routines GeosTomas/ Parallel copies of GEOS-Chem routines that reference TOMAS GeosUtil/ "Utility" modules (e.g. error_mod.f, file_mod.f, time_mod.f, etc. Headers/ Header files (define.h, CMN_SIZE, CMN_DIAG, etc.) ISOROPIA/ Directory where ISORROPIA II code resides KPP/ KPP solver directory structure bin/ Directory where executables are placed doc/ Directory where documentation is created help/ Directory for GEOS-Chem Help Screen lib/ Directory where library files are placed mod/ Directory where module files are placed obsolete/ Directory where obsolete versions of code are archived
ISORROPIA II consists of the following files:
Files in ISOROPIA/ subdirectory: --------------------------------- Makefile Makefile for ISORROPIA II code isoropiaIIcode.f Source code file with ISORROPIA II routines isrpia.inc ISOROPIA II header file with common blocks Files in GeosCore/ subdirectory: -------------------------------- isoropiaII_mod.f "Interface" code between GEOS-Chem and ISORROPIA II
Additional Documentation
Havala Pye (havala@caltech.edu) wrote:
- Documentation (including a user manual) for ISORROPIAII can be found on the ISORROPIA website.
- isoropiaIIcode.f is essentially ISOFWD.FOR and ISOCOM.FOR of the ISORROPIA II box model pasted together.
- For more information on ISORROPIA II, see
- Fountoukis, C. and Nenes, A.: ISORROPIA II: a computationally efficient thermodynamic equilibrium model for K+–Ca2+–Mg2+–NH4+–Na+–SO42−–NO3−–Cl−–H2O aerosols, Atmos. Chem. Phys., 7, 4639-4659, 2007. pdf
- The implementation by Pye et al. 2009 JGR did not include Ca, K, or Mg since dust emissions were not used.
--Bob Y. 10:28, 29 January 2010 (EST)
Validation
Text to be added
Previous issues now resolved
Outstanding issues
Aerosol pH
This issue is somewhat resolved.
Havala Pye (havala@caltech.edu) wrote:
- At the GEOS-Chem User's meeting (2009) Becky Alexander and her student Eric noted that ISORROPIAII sometimes returns a negative H+ concentration. In my tests, the negative values occurred in N. India and Western Russia area during limited times of the year. A quick fix has been implemented. A condition I tracked down was returning a negative [H+] when solving the HSO4 = H + SO4 equilibrium (CALCHS4 in isorropiaIIcode.f) when the actual answer should have been ~1e-27 mol/m3. (I plugged the same input values into a spreadsheet and it returned the same negative answer so it seems like a numerical precision issue.) For my case study, it came down to subtracting two numbers of very similar value (first 8 digits the same) which resulted in a negative. I put in a fix to reset H+ to 1d-30 in CALCHS4 if it goes negative.
--Bob Y. 10:29, 29 January 2010 (EST)