the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Implementation of the ISORROPIA-lite Aerosol Thermodynamics Model into the EMAC Chemistry Climate Model 2.56: Implications for Aerosol Composition and Acidity
Alexandros Milousis
Alexandra P. Tsimpidi
Holger Tost
Spyros N. Pandis
Athanasios Nenes
Astrid Kiendler-Scharr
Vlassis A. Karydis
Abstract. This study explores the differences in performance and results by various versions of the ISORROPIA thermodynamic module implemented within the global atmospheric chemistry model EMAC. Three different versions of the module were used, ISORROPIA II v1, ISORROPIA II v2.3, and ISORROPIA-lite. First, ISORROPIA II v2.3 replaced ISORROPIA II v1 in EMAC to improve pH predictions close to neutral conditions. The newly developed ISORROPIA-lite has been added to EMAC alongside ISORROPIA II v2.3. ISORROPIA-lite is more computationally efficient and assumes that atmospheric aerosols exist always as supersaturated aqueous (metastable) solutions while ISORROPIA II includes the option to allow the formation of solid salts at low RH conditions (stable state). The predictions of EMAC by employing all three aerosol thermodynamic models were compared to each other and evaluated against surface measurements from three regional observational networks (IMPROVE, EMEP, EANET) in the polluted Northern Hemisphere. The differences between ISORROPIA II v2.3 and ISORROPIA-lite were minimal in all comparisons with the normalized mean absolute difference for the concentrations of all major aerosol components being less than 10 % even when different phase state assumptions were used. The most notable differences were lower aerosol concentrations predicted by ISORROPIA-lite in regions with relative humidity in the range of 20 % to 60 % compared to the predictions of ISORROPIA II v2.3 in stable mode. The comparison against observations yielded satisfactory agreement especially over the US and Europe, but higher deviations over East Asia, where the overprediction of EMAC for nitrate was as high as 4 μg m-3 (~ 20 %). The mean annual aerosol pH predicted by ISORROPIA-lite was on average less than a unit lower than ISORROPIA II v2.3 in stable mode, mainly for coarse mode aerosols over Middle East. The use of ISORROPIA-lite accelerated EMAC by 5 % compared to the use of ISORROPIA II v2.3 even if the aerosol thermodynamic calculations consume a relatively small fraction of the EMAC computational time. ISORROPIA-lite can therefore be a reliable and computationally effective replacement of the previous thermodynamic module in EMAC.
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Alexandros Milousis et al.
Status: open (until 02 Nov 2023)
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CEC1: 'Comment on gmd-2023-178', Juan Antonio Añel, 13 Sep 2023
reply
Dear authors,
I would like to highlight a couple of issues related to compliance with our code availability policy. The main problem here is that the ISORROPIA II v2.3 and ISORROPIA-lite v1.0 codes are stored in a repository that we can not accept. You must store them in one of the repositories that we can accept, which are listed in our policy.
Also, although we are aware of the licensing issues with MESSY, we would like to ask you to store its code in a Zenodo private repository. In this way, you continue having control of its distribution, and at the same time, they are assured the long-term archival and the availability of a DOI to cite it.
Then, please, reply to this comment with the DOI and links for the new repositories, and remember to add this information to any newly reviewed version of your manuscript.
Regards,
Juan A. Añel
Geosci. Model Dev. Executive Editor
Citation: https://doi.org/10.5194/gmd-2023-178-CEC1
Alexandros Milousis et al.
Alexandros Milousis et al.
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