Multiphase processes in the EC-Earth model and their relevance to the atmospheric oxalate, sulfate, and iron cycles

[摘要] Understanding how multiphase processes affect theiron-containing aerosol cycle is key to predicting ocean biogeochemistrychanges and hence the feedback effects on climate. For this work, theEC-Earth Earth system model in its climate–chemistry configuration is usedto simulate the global atmospheric oxalate (OXL), sulfate (SO 4 2 - ),and iron (Fe) cycles after incorporating a comprehensive representation ofthe multiphase chemistry in cloud droplets and aerosol water. The modelconsiders a detailed gas-phase chemistry scheme, all major aerosolcomponents, and the partitioning of gases in aerosol and atmospheric waterphases. The dissolution of Fe-containing aerosols accounts kinetically forthe solution's acidity, oxalic acid, and irradiation. Aerosol acidity isexplicitly calculated in the model, both for accumulation and coarse modes,accounting for thermodynamic processes involving inorganic and crustalspecies from sea salt and dust. Simulations for present-day conditions (2000–2014) have been carried outwith both EC-Earth and the atmospheric composition component of the model instandalone mode driven by meteorological fields from ECMWF's ERA-Interimreanalysis. The calculated global budgets are presented and the linksbetween the (1) aqueous-phase processes, (2) aerosol dissolution, and (3)atmospheric composition are demonstrated and quantified. The model resultsare supported by comparison to available observations. We obtain an averageglobal OXL net chemical production of 12.615  ±  0.064 Tg yr −1 inEC-Earth, with glyoxal being by far the most important precursor of oxalicacid. In comparison to the ERA-Interim simulation, differences inatmospheric dynamics and the simulated weaker oxidizing capacity inEC-Earth overall result in a ∼  30 % lower OXL source. Onthe other hand, the more explicit representation of the aqueous-phasechemistry in EC-Earth compared to the previous versions of the model leadsto an overall ∼  20 % higher sulfate production, but this is stillwell correlated with atmospheric observations. The total Fe dissolution rate in EC-Earth is calculated at 0.806  ±  0.014 Tg yr −1 and is added to the primary dissolved Fe (DFe) sourcesfrom dust and combustion aerosols in the model (0.072  ±  0.001 Tg yr −1 ). The simulated DFe concentrations show a satisfactory comparisonwith available observations, indicating an atmospheric burden of ∼ 0.007 Tg, resulting in an overall atmospheric deposition flux into theglobal ocean of 0.376  ±  0.005 Tg yr −1 , which is well within the rangereported in the literature. All in all, this work is a first step towardsthe development of EC-Earth into an Earth system model with fullyinteractive bioavailable atmospheric Fe inputs to the marine biogeochemistrycomponent of the model.

[学科分类] 土木及结构工程学