Characterizing Surface Active Organics in Sea Spray Aerosol and Their Influence on Cloud Microphysics

Oceans produce one of the largest global natural sources of aerosol in the form of sea spray aerosol (SSA) particles which therefore play a large role in global climate dynamics. SSA particles are enriched in ocean-derived organic compounds, specifically surfactants, which influence the chemical properties of SSA and the potential for SSA particles to become cloud seeds. Hygroscopic growth studies performed on 100 nm laboratory-generated sea salt/sugar particles modeling SSA composition probed how individual surfactants influence particle water uptake. For particles comprised of sea salt/glucose, ionic surfactants increased particle hygroscopicity at low relative humidity (RH) and caused a reduction in the salt deliquescence relative humidity (DRH). Meanwhile nonionic surfactants had a minimal effect on sea salt/glucose particles across all RH setpoints. When glucose was then substituted with polysaccharide laminarin in sea salt/sugar/surfactant particles, surfactants caused a decrease in hygroscopicity at low RHs and the effect of ionic surfactants on the DRH was not observed. For RHs above the DRH, adding anionic or nonionic surfactants decreased water uptake for both sea salt/glucose and sea salt/laminarin particles. Cationic surfactants, however, did not dampen water uptake but even caused an increase in hygroscopicity at high RHs. The calculated cloud activation potential is higher for particles containing ionic surfactants and decreases with an increase in surfactant molecular size when the particle interfacial tension is used rather than the interfacial tension of pure water. The influence of surfactants on water uptake and cloud activation potential of particles containing sea salt/sugar depends on surfactant ionicity and molecular size, particle interfacial tension, and interactions between inorganic salt and organic species under different humidity conditions.

Reference:

Bramblett, R. L., & Frossard, A. A. (2022). Constraining the Effect of Surfactants on the Hygroscopic Growth of Model Sea Spray Aerosol Particles. The Journal of Physical Chemistry A, 126(46), 8695-8710.