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A Film- and Jet-Drop-Resolved Sea Spray Source Function for Size-Dependent Preferentially Enriched Marine Aerosol Constituents
Summary
When ocean bubbles pop, they release tiny droplets containing sea salt, microplastics, and harmful chemicals into the air that we breathe and that affects our weather and climate. Scientists created a new model that better predicts which droplets carry these dangerous substances and how they spread around the world. This matters because understanding how pollutants like microplastics and PFAS escape the ocean helps us predict human health risks and improve climate models.
Sea spray aerosol (SSA) influences atmospheric chemistry, cloud formation, and radiative forcing. It is produced by bubble bursting, which ejects film and jet drops that differ in size, production mechanism, and chemical mixing state. Accurately representing these transfer processes is increasingly important for SSA preferentially enriched with size-dependent constituents such as microplastics, algal toxins, and per- and polyfluoroalkyl substances (PFAS). However, most sea spray source functions (SSSFs) represent SSA production as a bulk size-resolved flux, limiting their ability to predict emissions of marine constituents whose enrichment depends on droplet production pathway. Here, we developed a film- and jet-drop-resolved SSSF from controlled measurements in a bubble bursting setup. The parameterization represents total SSA production as the sum of four lognormal modes, with separate film and jet components that can be coupled to pathway-specific enrichment factors (EFs). Applied globally, our SSSF predicts an average SSA number flux of approximately 2.74 × 10⁵ m⁻² s⁻¹ and sea salt mass emission of approximately 0.781 Pg yr⁻¹ for particles <10 μm. Using dissolved organic carbon (DOC) as a demonstration case, we show that coupling pathway-specific EFs to the film and jet components redistributes emitted DOC toward smaller aerosol sizes relative to a single-EF bulk approach. We further apply the framework to calcium, saccharides, bacteria, microplastics, and PFAS, showing that pathway-dependent enrichment can substantially alter magnitude and size distribution of predicted fluxes. This SSSF provides a pathway-resolved framework that can be readily integrated into global atmospheric models to improve predicted emissions of chemical and biological species.