A Giant Sea Salt Aerosol Source Function Using In-Situ Size Distributions and Novel Analysis Techniques

Giant sea salt aerosol (GSSA, particles > 1 µm in dry radius (r_d)) is hypothesized to constitute up to 94% of all coarse mode particles in typical marine environments. These particles play critical roles in radiative and cloud processes, however, sampling limitations like low atmospheric concentrations and particle loss in traditional aerosol samplers have hindered the observation and quantification of GSSA throughout the atmosphere. These constraints have henceforth limited our ability to estimate their global production, predict their vertical mixing within the marine boundary layer (MBL), and ultimately understand their impacts on aerosol-cloud interactions globally.

In this study, over 700 GSSA size distributions were collected using an impaction method across four open-ocean field campaigns: VOCALS, ICE-T, SOCRATES, and HAWAII. These distributions, gathered from altitudes ranging from 15 m to 1000 m above sea level, reveal a strong dependence on wind speeds across various geographic locations, as well as efficient mixing of particles up to 10 µm r_d throughout the MBL.

Utilizing these distributions, the authors have developed a new source function that models the effective production and entrainment of GSSA particles into the marine atmosphere by employing a continuous build-up technique. HYSPLIT trajectories, derived from ERA5 data, were used to analyze each sample's geographic and environmental history, which informed the development of this novel source function. Additionally, this new source function is compared to the most widely used sea salt source functions in major earth system models to understand how well existing production equations represent these in-situ observations.