US based researchers for the first time have observed the creation of ice crystals on individual atmospheric particles in the laboratory.
This observation gives an unprecedented glimpse at most critical but least understood parts of the process of cold clouds formation.
- Researchers had replicated heterogeneous ice nucleation process in which particle attracts water vapour and forms ice crystals.
- For this, they replicated suitable conditions found high above Earth’s surface at an altitude of about 6 kilometres where cirrus clouds form in the sky due to ice crystals.
- They witnessed formation of ice crystals in highly confined climate-controlled chamber in which atmospheric temperature, pressure and humidity conditions were maintained similar in atmosphere.
- For recreation of ice nucleation, researchers also used extremely small particles of a clay mineral called kaolinite. These particles were just 2–3 microns in size, or less than one-tenth width of a human hair.
- The kaolinite was then placed in a highly confined climate-controlled chamber of very small size, which was photographed by an environmental scanning electron microscope.
- It was found that nucleation occurred at temperatures as low as minus 68 degrees Celsius with relative humidity from about 70 to 80%.
Natural process of heterogeneous ice nucleation
At an altitude of about 6 kilometres, relative humidity is high and temperatures are very low. It forces water vapour to collect on any small particles floating in the atmosphere, before freezing in place as an ice deposit. In the atmosphere, such airborne particles could be almost anything, including volcanic ash, aircraft emissions, or even microbes.