Global models overestimate giant sea salt aerosol mixing ratio

Giant sea salt aerosol particles (GSSA) influence Earth’s radiative balance and aerosol-cloud interactions on a global scale. Both \textit{in situ} measurements and remote sensing techniques have worked to quantify aerosol concentrations worldwide, often linking these observations to local conditions such as wind speeds and wave heights in order to develop statistical relationships or source functions. These tools are then used to estimate the broader global and vertical distributions of GSSA beyond isolated measurements. Reanalysis products like the NASA Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), and the ECMWF Atmospheric Composition Reanalysis 4 (EAC4) are two main products that model sea salt aerosol (SSA) on a global scale. These products provide vertically resolved SSA mixing ratio estimates across five discrete bins, enabling continuous spatial and temporal coverage (3-hourly) in contrast to the point-based nature of \textit{in situ} data. In this study, we compare GSSA mass mixing ratio estimates from MERRA-2 and EAC4 with \textit{in situ} measurements collected during the VOCALS (2008), ICE-T (2011), and SOCRATES (2018) aircraft-based field campaigns. Our results show that both reanalysis products significantly overestimate GSSA mass mixing ratio in both magnitude and vertical distributions throughout and above the marine boundary layer. These discrepancies, ranging 2-4 orders of magnitude above observations on average, generate bias in studies aiming to assess the climate impact of GSSA that rely on these products to represent their global distribution.