Modeling Primary Marine Organic Aerosols

Primary marine aerosols are composed of sea salt and complex organic compounds originating from biochemical processes in the ocean. Their ubiquitous nature in the marine environment and their cloud-modifying and radiation-altering properties make them an important factor in the Earth system.

This project aimed to improve the characterization of primary marine aerosols in the Goddard Earth Observing System Model (GEOS) and model their impact on clouds more realistically. To this end, the main objectives were to: 1) include primary marine organic aerosols (PMOA) in GEOS and implement a parameterization of PMOA emissions; and 2) perform model simulations to assess the PMOA and their impact on clouds. After a thorough literature review we selected the Gantt et al. (2012) parameterization to estimate the organic mass fraction in nascent PMOA using the chlorophyll-a concentration and surface wind. We extended the GOCART aerosol model in GEOS to include PMOA and simulate their emissions, removal and transport in the atmosphere and also linked the PMOA tracers with two-moment cloud microphysics.

We performed model experiments to evaluate the PMOA and their effect on clouds. In these simulations, up to 60%-70% of the mass of emitted submicron size sea spray was organic matter. The available cloud condensation nuclei decreased in large parts in both the Northern and Southern Hemisphere, which we attributed to the decrease in sea salt, the increase in PMOA and its low hygroscopicity. The model- and more specifically clouds- responded to the introduction of PMOA, however longer simulations are required to quantify and understand better the effects of PMOA in GEOS.