Seasonal Dependence of Particle Number and Mass Production Efficiencies of Marine Aerosol Generated from Sargasso Seawater

AMANDA FROSSARD, Tret Burdette, Rachel Bramblett, William Keene, John Maben, Joanna Kinsey, David Kieber, Steven Beaupre, University of Georgia

     Abstract Number: 385
     Working Group: Aerosol Chemistry

Abstract
Atmospheric aerosol particles play important roles in directly and indirectly influencing global climate, through absorption and scattering of radiation as well as acting as cloud condensation nuclei (CCN). The ability of particles to act as CCN depends on their size and chemical composition, and the number of CCN modulates cloud droplet microphysics. Primary marine aerosol particles are emitted directly from wave breaking and bubble bursting at the sea surface and may contribute to CCN in the marine boundary layer. The number of particles emitted, as well as the physical and chemical properties of these particles, are dependent on a number of factors, including the physical and biochemical conditions of the seawater. Here, we show that the number production efficiency (PEnum) and the surfactant properties of primary marine aerosol particles vary as a function of season and resulting seawater physiochemical properties, while the mass production efficiency (PEmass) remained relatively constant. In summer 2021 and winter 2023, sea spray particles were produced using a marine aerosol generator on board the R/V Atlantic Explorer in the Sargasso Sea. PEnum and PEmass were calculated from size distributions and air entrainment rates. The average PEnum was ~2 times higher in the summer compared to the winter (411 x 10⁶ L^-1 and 200 x 10⁶ L^-1, respectively). The number size distributions were also shifted in the summer compared to the winter with a lower peak in PEnum diameter in the summer (52 nm) compared to the winter (64 nm). Seasonal differences in seawater physiochemistry likely contributed to the differences in PEnum. The lower sea surface temperature in the winter may have contributed to a higher seawater surface tension and altered bubble properties at the sea surface. Additionally, the concentrations of chlorophyll a were low overall but slightly higher in the winter, indicating different mixing profiles and potential differences in bubble properties. These seasonal differences demonstrate that PEnum will also vary widely for different seawater types and depend largely on the physicochemical properties of the seawater.