Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Model description paper
24 Oct 2011
Review status
This discussion paper is a preprint. A revision of the manuscript for further review has not been submitted.
Description of EQSAM4: gas-liquid-solid partitioning model for global simulations
S. Metzger1, B. Steil1, L. Xu2, J. E. Penner2, and J. Lelieveld1,3,4 1Max Planck Institute for Chemistry, Mainz, Germany
2University of Michigan, Ann Arbor, Michigan, USA
3The Cyprus Institute, Nicosia, Cyprus
4King Saud University, Riyadh, Saudi Arabia
Abstract. We introduce version 4 of the EQuilibrium Simplified Aerosol Model (EQSAM4), which is part of our aerosol chemistry-microphysics module (GMXe) and chemistry-climate model (EMAC). We focus on the relative humidity of deliquescence (RHD) based water uptake of atmospheric aerosols, as this is important for atmospheric chemistry and climate modeling, e.g. to calculate the aerosol optical depth (AOD). Since the main EQSAM4 applications will involve large-scale, long-term and high-resolution atmospheric chemistry-climate modeling with EMAC, computational efficiency is an important requirement. EQSAM4 parameterizes the composition and water uptake of multicomponent atmospheric aerosols by considering the gas-liquid-solid partitioning of single and mixed solutes. EQSAM4 builds on analytical, and hence CPU efficient, aerosol hygroscopic growth parameterizations to compute the aerosol liquid water content (AWC). The parameterizations are described in the companion paper (Metzger et al., 2011) and only require a compound specific coefficient νi to derive the single solute molality and the AWC for the whole range of water activity (aw). νi is pre-calculated and applied during runtime by using internal look-up tables. Here, the EQSAM4 equilibrium model is described and compared to the more explicit thermodynamic model ISORROPIA II. Both models are imbedded in EMAC/GMXe. Box model inter-comparisons, including the reference model E-AIM, and global simulations with EMAC show that gas-particle partitioning, including semi-volatiles and water, is in good agreement. A more comprehensive box model inter-comparison of EQSAM4 with EQUISOLV II is subject of the revised publication of Xu et al. (2009), i.e. Xu et al. (2011).

Citation: Metzger, S., Steil, B., Xu, L., Penner, J. E., and Lelieveld, J.: Description of EQSAM4: gas-liquid-solid partitioning model for global simulations, Geosci. Model Dev. Discuss.,, in review, 2011.
S. Metzger et al.
Interactive discussionStatus: closed (peer review stopped)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
RC C1193: 'Review comment on "Reformulating atmospheric aerosol thermodynamics... by Metzger et al."', Ralph Lescroart, 16 Dec 2011 Printer-friendly Version 
RC C1254: 'Reviewer comments', Anonymous Referee #2, 28 Dec 2011 Printer-friendly Version Supplement 
AC C1812: 'Final reply', Swen Metzger, 26 Jun 2012 Printer-friendly Version 
S. Metzger et al.
S. Metzger et al.


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