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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/gmd-2019-58
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gmd-2019-58
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model evaluation paper 07 Mar 2019

Model evaluation paper | 07 Mar 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).

Revised treatment of wet scavenging processes dramatically improves GEOS-Chem 12.0.0 simulations of nitric acid, nitrate, and ammonium over the United States

Gan Luo, Fangqun Yu, and James Schwab Gan Luo et al.
  • Atmospheric Sciences Research Center, University at Albany

Abstract. The widely used community model GEOS-Chem 12.0.0 and previous versions have been recognized to significantly overestimate the concentrations of gaseous nitric acid, aerosol nitrate, and aerosol ammonium over the United States. The concentrations of nitric acid are also significantly over-predicted in most global models participating a recent model inter-comparison study. In this study, we show that most or all of this overestimation issue appears to be associated with wet scavenging processes. Replacement of constant in-cloud condensation water (ICCW) assumed in GEOS-Chem standard versions with one varying with location and time from the assimilated meteorology significantly reduces mass loadings of nitrate and ammonium during the wintertime, while the employment of an empirical washout rate for nitric acid significantly decreases mass concentrations of nitric acid and ammonium during the summertime. Compared to the standard version, GEOS-Chem with updated ICCW and washout rate significantly reduces the simulated annual mean mass concentrations of nitric acid, nitrate, and ammonium at surface mentoring network sites in US, from 2.04 to 1.03 μg m-3, 1.89 to 0.88 μg m-3, 1.09 to 0.68 μg m-3, respectively, in much better agreement with corresponding observed values of 0.83, 0.70, and 0.60 μg m-3, respectively. In addition, the agreement of model simulated seasonal variations of corresponding species with measurements is also improved. The updated wet scavenging scheme improves the skill of the model in predicting nitric acid, nitrate, and ammonium concentrations which are important species for air quality and climate.

Gan Luo et al.
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Short summary
GEOS-Chem 12.0.0 has been recognized to significantly overestimate the concentrations of gaseous nitric acid, aerosol nitrate, and aerosol ammonium over the United States. In this study, we show that most or all of this overestimation issue appears to be associated with wet scavenging processes. With the updated wet scavenging scheme in this work, we successfully improve the skill of the model in predicting the three species concentrations which are important for air quality and climate studies.
GEOS-Chem 12.0.0 has been recognized to significantly overestimate the concentrations of gaseous...
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