Understanding how ice crystals form in clouds

How ice forms on the surfaces of mineral dust particles in the atmosphere has been revealed by a team from UCL and the Karlsruhe Institute of Technology (KIT) in Germany. More than 90% of precipitation over land relies on the formation of ice crystals on airborne aerosol particles but why only a tiny fraction of all atmospheric particles can initiate ice growth is unknown. The scarce particles are crucial to Earth's climate as water in clouds can only freeze, generating rain, snow, sleet or hail, when they are present to act as a base from which ice crystals grow. The study found ice starts to form at exposed surface defects, such as edges, cracks and small depressions, on the surface of feldspar - an important mineral dust found in the atmosphere and known to help ice form in clouds. 'Feldspar is one of the most active atmospheric ice nucleating agents but why it is so good at making ice has remained unclear. By identifying the active sites for ice nucleation on feldspar, we've found an important piece of the puzzle of how ice and precipitation forms in clouds at a molecular level,' said study co-author Professor Angelos Michaelides (UCL Physics & Astronomy and the London Centre for Nanotechnology). The team used electron microscopy and computer simulations to understand how ice forms on feldspar at the microscopic level.