Terrestrial and airborne non‐bacterial ice nuclei

To freeze above −36.5 °C, water requires the presence of an ice nucleus (IN). These can be inert particles or living or dead biological material. As they are the most efficient, inducing freezing at up to −1.8 °C, bacteria are the most widely studied biological IN. Here, we show that there is a huge repository of IN in lichens which comprise a large biomass and are able to become airborne. The lichen IN are similar to those we have detected in urban air, exhibiting heat sensitivity but resistance to lysozyme. This suggests many airborne IN are non‐bacterial and that eukaryotic IN may be more important to atmospheric processes than previously thought. Copyright © 2009 Royal Meteorological Society