Abstract
Abstract. SOCOL-AERv1 was developed as an aerosol–chemistry–climate model to study the stratospheric sulfur cycle and its influence on climate and the ozone layer. It includes a sectional aerosol model that tracks the sulfate particle size distribution in 40 size bins, between 0.39 nm and 3.2 µm. Sheng et al. (2015) showed that SOCOL-AERv1 successfully matched observable quantities related to stratospheric aerosol. In the meantime, SOCOL-AER has undergone significant improvements and more observational datasets have become available. In producing SOCOL-AERv2 we have implemented several updates to the model: adding interactive deposition schemes, improving the sulfate mass and particle number conservation, and expanding the tropospheric chemistry scheme. We compare the two versions of the model with background stratospheric sulfate aerosol observations, stratospheric aerosol evolution after Pinatubo, and ground-based sulfur deposition networks. SOCOL-AERv2 shows similar levels of agreement as SOCOL-AERv1 with satellite-measured extinctions and in situ optical particle counter (OPC) balloon flights. The volcanically quiescent total stratospheric aerosol burden simulated in SOCOL-AERv2 has increased from 109 Gg of sulfur (S) to 160 Gg S, matching the newly available satellite estimate of 165 Gg S. However, SOCOL-AERv2 simulates too high cross-tropopause transport of tropospheric SO2 and/or sulfate aerosol, leading to an overestimation of lower stratospheric aerosol. Due to the current lack of upper tropospheric SO2 measurements and the neglect of organic aerosol in the model, the lower stratospheric bias of SOCOL-AERv2 was not further improved. Model performance under volcanically perturbed conditions has also undergone some changes, resulting in a slightly shorter volcanic aerosol lifetime after the Pinatubo eruption. With the improved deposition schemes of SOCOL-AERv2, simulated sulfur wet deposition fluxes are within a factor of 2 of measured deposition fluxes at 78 % of the measurement stations globally, an agreement which is on par with previous model intercomparison studies. Because of these improvements, SOCOL-AERv2 will be better suited to studying changes in atmospheric sulfur deposition due to variations in climate and emissions.
Highlights
The atmospheric sulfur cycle is of significance for climate, atmospheric chemistry, ecosystems, agriculture, and human health
The model succeeded in reproducing the observed background stratospheric aerosol extinctions compared to the Stratospheric Aerosol and Gas Experiment II (SAGE II) and Halogen Occultation Experiment (HALOE) measurements (Thomason, 2012), as well as the particle size distributions measured by optical particle counters (OPCs) in the midlatitudes (Deshler et al, 2003; Deshler, 2008)
We discuss the relevant impacts of each stage of code changes on the atmospheric sulfur cycle
Summary
The atmospheric sulfur cycle is of significance for climate, atmospheric chemistry, ecosystems, agriculture, and human health. H2SO4-containing particles are removed by wet and dry deposition, closing the atmospheric sulfur cycle (Kremser et al, 2016). SOCOL-AERv1 is a model with a sectional scheme that divides the sulfate aerosol size distribution into 40 bins (Sheng et al, 2015). The model succeeded in reproducing the observed background stratospheric aerosol extinctions compared to the Stratospheric Aerosol and Gas Experiment II (SAGE II) and Halogen Occultation Experiment (HALOE) measurements (Thomason, 2012), as well as the particle size distributions measured by optical particle counters (OPCs) in the midlatitudes (Deshler et al, 2003; Deshler, 2008). Despite the good agreement of SOCOL-AERv1 with stratospheric aerosol observations, several aspects of the tropospheric sulfur cycle are treated in a coarse manner. We compare the model with stratospheric aerosol observations, from both nonvolcanic background and post-Pinatubo periods, as well as with surface measurements of wet and dry deposition fluxes.
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