Heterogeneous ice nucleation ability of aerosol particles generated from Arctic sea surface microlayer and surface seawater samples at cirrus temperatures
<p>Sea spray aerosol particles are a recognised type of ice-nucleating particles under mixed-phase cloud conditions. Entities that are responsible for the heterogeneous ice nucleation ability include intact or fragmented cells of marine microorganisms as well as organic matter released by cell...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/13903/2021/acp-21-13903-2021.pdf |
| Summary: | <p>Sea spray aerosol particles are a recognised type of
ice-nucleating particles under mixed-phase cloud conditions. Entities that
are responsible for the heterogeneous ice nucleation ability include intact
or fragmented cells of marine microorganisms as well as organic matter
released by cell exudation. Only a small fraction of sea spray aerosol is
transported to the upper troposphere, but there are indications from
mass-spectrometric analyses of the residuals of sublimated cirrus particles
that sea salt could also contribute to heterogeneous ice nucleation under
cirrus conditions. Experimental studies on the heterogeneous ice nucleation
ability of sea spray aerosol particles and their proxies at temperatures
below 235 <span class="inline-formula">K</span> are still scarce. In our article, we summarise previous
measurements and present a new set of ice nucleation experiments at cirrus
temperatures with particles generated from sea surface microlayer and
surface seawater samples collected in three different regions of the Arctic
and from a laboratory-grown diatom culture (<i>Skeletonema marinoi</i>). The particles were suspended in the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber and ice formation was induced by expansion cooling. We confirmed that under cirrus conditions, apart from the
ice-nucleating entities mentioned above, also crystalline inorganic salt
constituents can contribute to heterogeneous ice formation. This takes place
at temperatures below 220 <span class="inline-formula">K</span>, where we observed in all experiments a strong
immersion freezing mode due to the only partially deliquesced inorganic
salts. The inferred ice nucleation active surface site densities for this
nucleation mode reached a maximum of about <span class="inline-formula">5×10<sup>10</sup></span> <span class="inline-formula">m<sup>−2</sup></span>
at an ice saturation ratio of 1.3. Much smaller densities in the range of
10<span class="inline-formula"><sup>8</sup></span>–10<span class="inline-formula"><sup>9</sup></span> <span class="inline-formula">m<sup>−2</sup></span> were observed at temperatures between 220 and
235 <span class="inline-formula">K</span>, where the inorganic salts fully deliquesced and only the organic
matter and/or algal cells and cell debris could contribute to heterogeneous
ice formation. These values are 2 orders of magnitude smaller than those previously reported for particles generated from microlayer suspensions
collected in temperate and subtropical zones. While this difference might
simply underline the strong variability of the number of ice-nucleating entities in the sea surface microlayer across different geographical regions, we also discuss how instrumental parameters like the aerosolisation
method and the ice nucleation measurement technique might affect the comparability of the results amongst different studies.</p> |
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| ISSN: | 1680-7316 1680-7324 |