Understanding the Role of Marine Surface Active Compounds in the Microphysical Properties of Primary Marine Aerosol

The ocean-air interface is a critical site for the transfer and exchange of both chemical and biological components between the atmosphere and the ocean. The sea surface microlayer serves as the main interface and is composed of higher concentrations of organic matter, including surface active compounds, than bulk seawater. These surface active compounds have the ability to change the interfacial tension of the water surface and influence how organic matter is transported into the marine boundary layer by bubble bursting and the production of primary marine aerosol particles. As air bubbles beneath the surface rise, they scavenge surface active compounds and other organics which are then released into the atmosphere when the bubbles burst at the ocean-air interface. In addition to particle size, the composition of primary marine aerosol particles defines their properties and determines their fate in the atmosphere. Surface active compounds derived from the ocean and their effect on the surface tension of aerosol particles has been up until recently neglected in model calculations of particle hygroscopic growth. Accurately modeling particle hygroscopic growth is crucial for understanding the lifetime of primary marine aerosol particles in the marine boundary layer, whether they are activated into cloud droplets or deposited back to the sea surface, as well as their impact on Earth’s climate. In this study, we used a Humidified Tandem Differential Mobility Analyzer (HTDMA) to study the hygroscopic growth of model primary marine aerosol particles over a range of particle sizes and compositions. Model primary aerosol particles contained surfactants with properties similar to those extracted from surface seawater. We observed an increase in the hygroscopic growth factors of aerosol particles containing surfactants, compared to those comprised of only sea salt. This demonstrates the influence of surface active organics in the sea surface on the potential of marine particles to act as cloud condensation nuclei.