Preprints
https://doi.org/10.5194/gmd-2023-178
https://doi.org/10.5194/gmd-2023-178
Submitted as: model evaluation paper
 | 
07 Sep 2023
Submitted as: model evaluation paper |  | 07 Sep 2023
Status: this preprint is currently under review for the journal GMD.

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, and 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.

Alexandros Milousis et al.

Status: open (until 02 Nov 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CEC1: 'Comment on gmd-2023-178', Juan Antonio Añel, 13 Sep 2023 reply

Alexandros Milousis et al.

Alexandros Milousis et al.

Viewed

Total article views: 229 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
178 47 4 229 10 1 1
  • HTML: 178
  • PDF: 47
  • XML: 4
  • Total: 229
  • Supplement: 10
  • BibTeX: 1
  • EndNote: 1
Views and downloads (calculated since 07 Sep 2023)
Cumulative views and downloads (calculated since 07 Sep 2023)

Viewed (geographical distribution)

Total article views: 212 (including HTML, PDF, and XML) Thereof 212 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 23 Sep 2023
Download
Short summary
This study aims to evaluate the newly developed ISORROPIA-lite aerosol thermodynamic module within the EMAC model and explore discrepancies in global atmospheric simulations of aerosol composition and acidity by utilizing different aerosol phase states. Even though local differences were found in regions where the RH ranged from 20 % to 60 %, on a global scale the results are similar. Therefore, ISORROPIA-lite can be a reliable and computationally effective replacement of ISORROPIA-II in EMAC.