Observationally constrained analysis of sulfur species in the marine troposphere

The NASA Earth Venture Suborbital (EVS-2) Atmospheric Tomography Mission (ATom) provided rich gas and aerosol measurements over the global oceans. In this study, we investigate the sulfur species of dimethyl sulfide (DMS), sulfur dioxide (SO2), methane sulfonic acid (MSA), and sulfate (SO4) that were measured during the ATom aircraft campaigns and simulated by five AeroCom models. This study focuses on remote regions over the Pacific, Atlantic, and Southern Oceans from near the surface to ~12 km altitude and covers all four seasons. We examine the vertical and seasonal variations of these sulfur species over tropical, mid-, and high latitude regions in both hemispheres. We identify their origins from land versus ocean and from anthropogenic versus natural sources with sensitivity studies by applying tagged tracers linking to emission types and regions. Using the GEOS model, we also investigate impact of cloud simulation (i.e., one-moment bulk cloud module, 1MOM vs two-moment cloud microphysics module, 2MOM) on the sulfur cycle and identify critical mechanisms of cloud impact by performing process-level budget analyses. Generally, SO4 has a better model-observation agreement than DMS, SO2 and MSA, and there are much larger DMS simulated concentrations close to the sea surface than measured, indicating all model DMS emissions may be too high. Anthropogenic emissions are the dominant source (44-60% of the total amount) for atmospheric SO4 simulated along ATom flight tracks in almost every altitude, followed by volcanic eruptions (18-33%) and oceanic sources (16-28%). GEOS SO4 simulations differ significantly between the 1MOM and 2MOM cloud schemes, with the sulfate chemical production via aqueous phase reactions seeming to be the critical process.