Feldspar minerals as efficient deposition ice nuclei
Mineral dusts are well known to be efficient ice nuclei, where the source of this efficiency has typically been attributed to the presence of clay minerals such as illite and kaolinite. However, the ice nucleating abilities of the more minor mineralogical components have not been as extensively exam...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2013-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/13/11175/2013/acp-13-11175-2013.pdf |
| Summary: | Mineral dusts are well known to be efficient ice nuclei, where the source of
this efficiency has typically been attributed to the presence of clay
minerals such as illite and kaolinite. However, the ice nucleating abilities
of the more minor mineralogical components have not been as extensively
examined. As a result, the deposition ice nucleation abilities of 24
atmospherically relevant mineral samples have been studied, using a
continuous flow diffusion chamber at −40.0 ± 0.3 °C and particles
size-selected at 200 nm. By focussing on using the same experimental
procedure for all experiments, a relative ranking of the ice nucleating
abilities of the samples was achieved. In addition, the ice nucleation
behaviour of the pure minerals is compared to that of complex mixtures, such
as Arizona Test Dust (ATD) and Mojave Desert Dust (MDD), and to lead iodide,
which has been previously proposed for cloud seeding. Lead iodide was the
most efficient ice nucleus (IN), requiring a critical relative humidity with
respect to ice (RH<sub>i</sub>) of 122.0 ± 2.0% to activate 0.1% of
the particles. MDD (RH<sub>i</sub>) 126.3 ± 3.4%) and ATD (RH<sub>i</sub> 129.5 ± 5.1%)
have lower but comparable activity. From a set of clay
minerals (kaolinite, illite, montmorillonite), non-clay minerals (e.g.
hematite, magnetite, calcite, cerussite, quartz), and feldspar minerals
(orthoclase, plagioclase) present in the atmospheric dusts, it was found
that the feldspar minerals (particularly orthoclase) and some clays
(particularly kaolinite) were the most efficient ice nuclei. Orthoclase and
plagioclase were found to have critical RH<sub>i</sub> values of 127.1 ± 6.3% and 136.2 ± 1.3%, respectively. The presence of feldspars
(specifically orthoclase) may play a significant role in the IN behaviour of
mineral dusts despite their lower percentage in composition relative to clay
minerals. |
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| ISSN: | 1680-7316 1680-7324 |