Sources and Properties of Cloud Condensation Nuclei in the Marine Boundary Layer

Abstract:

Breaking waves on the ocean surface result in the entrainment of air bubbles that scavenge organic matter from seawater as they rise to the surface. When injected to the atmosphere, the bubbles burst and yield primary super- and sub-micrometer sea spray aerosol (SSA). Understanding the source, emission, cloud condensation nuclei (CCN) activity, and direct radiative forcing of SSA is required for accurately modeling its impact on tropospheric chemistry, marine boundary layer cloud properties, and Earth’s radiation balance. We report here measurements of the properties of freshly emitted sea spray aerosols produced with an in situ particle generator (Sea Sweep) during two cruises in the North Atlantic. The first cruise was conducted in August of 2012 and the second in May and June of 2014. Particular emphasis was put on the measurement of the composition, number concentration, and CCN activity of sub-180 nm SSA as this is the size range that dominates the marine boundary layer CCN population. During both cruises, ocean regions with a range of surface seawater chlorophyll-a (Chl-a), particulate organic carbon (POC), and dissolved organic carbon (DOC) concentrations were targeted. Relationships between these surface seawater parameters and the enrichment of organic carbon in sub-180 nm SSA and the CCN activity of monodisperse aerosol ranging between 40 and 110 nm will be presented.

During the 2014 cruise, sustained periods of wind speeds greater than 15 m/s were encountered which allowed for the measurement of ambient sub-180 nm and submicrometer aerosol under high wind conditions. Properties of SSA generated with Sea Sweep and ambient marine boundary layer aerosol present under high wind conditions will be presented and compared. Measured properties include particle number size distribution and chemical composition, volatility at 230 degrees C, and CCN activity.

Properties of freshly emitted sea spray aerosol and ambient aerosol measured under high wind conditions from the North Atlantic will be compared to what might be expected over the remote Southern Ocean given differences in surface seawater organic matter and atmospheric wind and transport patterns.