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[ACG41-12] Ice nucleation activity of the particles emitted from sea surface microlayer in Tsukumo Bay, Japan
Keywords:ice nuclei, aerosol particle, sea surface microlayer
In the freezing experiment, these samples froze in the temperature range of -15.5 degC to -24.1 degC, and the number concentrations of ice nucleating particles at -20 degC were calculated to be in the range 5.4 E + 4 pieces / L to 1.1 E + 6 particles / L. These results were consistent with the results reported for SML collected in the Arctic Ocean and North Atlantic (Wilson et al., 2015, Irish et al., 2017). Additionally, these freezing temperatures and number concentrations of ice nucleating particles of the SML and sea foam were significantly higher than the bulk seawater collected at the same location. These results suggested that the ice nucleating particles are ubiquitously concentrated in the sea surface microlayer. When compared with other environmental parameters, the freezing temperature of SML, sea foam and bulk seawater, was found not to correlate with the chlorophyll a concentration. Meanwhile, the concentrations of both the Coomassie Stained Particles (CSP) originating from protein, and the Transparent Exopolymer Particles (TEP) originating from polysaccharides correlated well with the freezing temperature (Fig. 1).
These results suggested that the ice nucleation by SML, sea foam, and sea spray aerosols emitted from the ocean in general are caused by organic matter originating from marine organisms such as protein and polysaccharide.
In order to compare the ice nucleation activities of SML relative to the mineral dust (Arizona Test Dust: ATD) having high ice nucleation activity, additional experiment was conducted by generating SML particles and measuring the particle number size distributions along with the sampling for the freezing temperature measurements. As a result, the SML particles were found to exhibit similar ice nucleation active site (INAS) density as the reference ATD. In other words, the particles emitted from SML are suggested to have ice nucleation activity comparable to mineral dust in the atmosphere.
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