Modelling emission and transport of key components of primary marine organic aerosol using the global aerosol-climate model ECHAM6.3–HAM2.3

Abstract. Primary marine organic aerosol (PMOA) contributes significantly to the aerosol loading over remote oceanic regions, where sea spray dominates aerosol production in the lower troposphere, and plays an important role in aerosol-cloud-climate interactions. The sea-atmosphere transfer of organic components depends on their abundance at the ocean surface and their physicochemical characteristics. We introduce a novel approach for representing the ocean concentration of the most abundant organic groups in seawater that are relevant to aerosols. By apportioning the phytoplankton exuded dissolved organic carbon, modelled in the biogeochemistry model FESOM2.1-REcoM3, three biomolecule groups are computed (dissolved carboxylic acidic containing polysaccharides (PCHO), dissolved combined amino acids (DCAA), and polar lipids (PL)). The transfer of these marine groups to the atmosphere is represented by the OCEANFILMS (Organic Compounds from Ecosystems to Aerosols: Natural Films and Interfaces via Langmuir Molecular Surfactants) parameterization which is implemented in the aerosol-climate model ECHAM6.3–HAM2.3 to represent the emission and transport processes in the atmosphere. The concentration of biomolecules in the ocean serves as the bottom boundary condition for the PMOA simulation within the aerosol model. Among the simulated organic groups in seawater, modelled PCHO is the most prevalent, followed by DCAA and PL. Conversely, PL contributes the most to the organic matter in aerosols, given the high air-seawater affinity of lipids compared to the other groups. Biomolecules exhibit minor variations in Equatorial waters, whereas strong seasonal patterns are observed towards the polar regions. The global aerosol model simulations indicate that PMOA emission fluxes are primarily influenced by marine biological activity and surface wind conditions. Based on the most comprehensive evaluation to date, the computed levels of biomolecules in the ocean and species-resolved PMOA concentrations are compared with ground-based measurements across the globe. The comparison shows a strong agreement, given the uncertainties in model assumptions and measurements. Since PMOA is emitted together with sea salt, model biases in the representation of the marine organic aerosol groups are caused by uncertainties in the simulated sea salt concentrations. A comparison with a set of long-range in-situ aircraft measurements indicates that by including PMOA in the model, the representation of organic aerosols in the Southern Oceans is significantly improved.