Wind-driven emission of marine ice-nucleating particles in the Scripps Ocean-Atmosphere Research Simulator (SOARS)

Abstract. Sea spray aerosol (SSA) represents one of the most abundant natural aerosol types, contributing significantly to global aerosol mass and aerosol optical depth, as well as to both the magnitude of and the uncertainty in aerosol radiative forcing. In addition to its direct effects, SSA can also serve as ice-nucleating particles (INPs), which are required for the initiation of cloud glaciation at temperatures warmer than ca. −36 °C. This study presents initial results from the CHaracterizing Atmosphere-Ocean parameters in SOARS (CHAOS) mesocosm campaign, which was conducted in the new Scripps Ocean-Atmosphere Research Simulator (SOARS) wind–wave channel. SOARS allows for isolation of individual factors, such as wave height, wind speed, water temperature, or biological state, and can carefully vary them in a controlled manner. Here, we focus on the influence of wind speed on the emission of SSA and INPs. In agreement with recent Southern Ocean measurements, online INP concentrations during CHAOS showed an increasing relationship with wind speed, whereas offline CHAOS INP concentrations did not, which may be related to sampling inlet differences. Changes in the INP activated fraction, dominant INP particle morphology, and INP composition were seen to vary with wind. Seawater ice-nucleating entity concentrations during CHAOS were stable over time, indicating that changes in atmospheric INPs were driven by wind speed and wave-breaking mechanics rather than variations in seawater chemistry or biology. While specific emission mechanisms remain elusive, these observations may help explain some of the variability in INP concentration and composition that has been seen in ambient measurements.