Measurements of Aerosol Particle and Cloud Properties over the Southern Ocean

The 2018 Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) was designed to improve our understanding of cloud properties and their interactions with aerosol particles over the remote Southern Ocean. In this region, existing measurements are scarce, and climate models don’t accurately predict cloud amount, phase or radiative properties. We will present measurements of the size distribution and chemical properties of aerosol particles at different altitudes above the Southern Ocean, in and out of clouds. These data will be used to help explain aerosol sources and their relationship to concentrations of cloud condensation nuclei and ice nucleating particles, as well as to the physical properties of Southern Ocean clouds.

Aerosol particles were sampled by a variety of instruments behind an airborne counterflow virtual impactor (CVI) inlet, which separated hydrometeors from interstitial aerosol and gases and evaporated them. Individual residual particles from cloud droplets and ice were measured and collected. Without the counterflow, the CVI was used as an aerosol particle inlet above and below clouds. Both heated and unheated measurements were made to assess aerosol volatility. Particles in cloud-active sizes were impacted for later analysis of inorganic and organic composition by transmission electron microscopy/energy dispersive X-ray spectrometry (TEM/EDS) and scanning transmission X-ray microscopy/near edge X-ray absorption fine structure (STXM/NEXAFS). In-situ, particles were measured with an optical particle counter (for size distribution), a continuous flow diffusion chamber (for ice nucleating particle concentrations), and a Wideband Integrated Bioaerosol Spectrometer (for fluorescent bioaerosol concentrations). In addition, direct measurements of cloud condensation nuclei and cloud physical properties were made. A variety of these measurements and how they are being used to understand aerosol interactions with Southern Ocean clouds will be presented.