Abstract
Understanding how multiphase processes affect the iron-containing aerosol cycle is key to predict ocean biogeochemistry changes and hence the feedback effects on climate. For this work, the EC-Earth Earth system model in its climate-chemistry configuration is used to simulate the global atmospheric oxalate (OXL), sulfate (SO42−), and iron (Fe) cycles, after incorporating a comprehensive representation of the multiphase chemistry in cloud droplets and aerosol water. The model considers a detailed gas-phase chemistry scheme, all major aerosol components, and the partitioning of gases in aerosol and atmospheric water phases. The dissolution of Fe-containing aerosols accounts kinetically for the solution’s acidity, oxalic acid, and irradiation. Aerosol acidity is explicitly calculated in the model, both for accumulation and coarse modes, accounting for thermodynamic processes involving inorganic and crustal species from sea salt and dust. Simulations for present-day conditions (2000–2014) have been carried out with both EC-Earth and the atmospheric composition component of the model in standalone mode driven by meteorological fields from ECMWF’s ERA-Interim reanalysis. The calculated global budgets are presented and the links between the 1) aqueous-phase processes, 2) aerosol dissolution, and 3) atmospheric composition, are demonstrated and quantified. The model results are supported by comparison to available observations. We obtain an average global OXL net chemical production of 12.61 ± 0.06 Tg yr−1 in EC-Earth, with glyoxal being by far the most important precursor of oxalic acid. In comparison to the ERA-Interim simulation, differences in atmospheric dynamics as well as the simulated weaker oxidizing capacity in EC-Earth result overall in a ~30 % lower OXL source. On the other hand, the more explicit representation of the aqueous-phase chemistry in EC-Earth compared to the previous versions of the model leads to an overall ~20 % higher sulfate production, but still well correlated with atmospheric observations. The total Fe dissolution rate in EC-Earth is calculated at 0.806 ± 0.014 Tg Fe yr−1 and is added to the primary dissolved Fe (DFe) sources from dust and combustion aerosols in the model (0.072 ± 0.001 Tg Fe yr−1). The simulated DFe concentrations show a satisfactory comparison with available observations, indicating an atmospheric burden of ∼0.007 Tg Fe, and overall resulting in an atmospheric deposition flux into the global ocean of 0.376 ± 0.005 Tg Fe yr−1, well within the range reported in the literature. All in all, this work is a first step towards the development of EC-Earth into an Earth System Model with fully interactive bioavailable atmospheric Fe inputs to the marine biogeochemistry component of the model.
Highlights
We describe the multiphase chemistry scheme used to simulate the atmospheric OXL, SO42, and Fe cycles, along with the respective developments for the primary soil and combustion sources applied in the model
Since SSTs and sea-ice concentrations are prescribed in our EC-Earth atmosphere-only simulations, the long-term means of tropospheric temperatures and water vapor are not expected to differ significantly to ERA-Interim close to the surface levels, as indicated by the low differences in the oxidation by hydroxyl (OH) levels of the two simulations at low altitudes (Fig. S1b)
This work documents the implementation of a detailed multiphase chemistry scheme in the EC-Earth3 Earth system model, aiming to provide consistent estimates of the atmospheric concentrations of the Fe-containing aerosols, along with the species that modulate its atmospheric processing, i.e., OXL and SO42
Summary
Fog, and deliquescent aerosols host chemical reactions involving inorganic and organic polar atmospheric compounds (Calvert et al, 1985; Chameides and Davis, 1983; Collett et al, 1999; Donaldson and Valsaraj, 2010; Jacob, 1986; Lelieveld and Crutzen, 1991). These reactions result in the production of species that can neither be formed via gas-phase processes 50 directly, nor explained solely by primary sources. The atmospheric processing of Fe-containing minerals, i.e., the conversion from insoluble to soluble that is readily available Fe for marine organisms, is a central step in the atmospheric and marine Fe cycles and directly connected to atmospheric multiphase processes
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