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In the absence of catalysts for freezing, water can remain in a metastable liquid state at temperatures well below 0°C. Water in the liquid state at temperatures below 0°C is referred to as supercooled water. Spontaneous freezing of supercooled water occurs below –39°C. Hence, freezing catalysts are clearly essential for many natural freezing processes.
A wide range of substances are able to catalyze ice nucleation. Various inorganic crystalline solids (the most well known of which is silver iodide), amino acid crystals, monolayers of long chain alcohols and organic compounds such as phloroglucinol and metaldehyde can catalyse the freezing of supercooled water. Substances that are abundant in atmospheric aerosols, such as soot, mineral dusts and metallic particles are also ice nucleation active (INA). In the atmosphere near forests, INA combinations of terpenes and of other tree oils with iodine have been detected. But among all the different ice nucleators naturally present in the environment, biological ice nucleators are among the most active. INA organisms include plants, fungi, bacteria, vertebrates and invertebrates.
Atmosphere physicists have long sought the ice nucleators responsible for various freezing processes in nature. Several decades ago, when INA micro-organisms were detected in atmospheric aerosols and in clouds, biologists joined in the heightened effort to investigate the role of biological ice nucleators in atmospheric processes that require freezing - such as rain formation. Recently there has been renewed interest in the unanswered questions about this role. Assessments of an atmospheric role for biological ice nucleators are gathering momentum as techniques of detection improve, as understanding of biological sources is growing, and as observations and modelling of clouds elucidate the role of early ice nucleation in the formation of precipitation and in determining other cloud characteristics. Progress in understanding the role of biological ice nucleators in these atmospheric processes that define our climate requires close collaboration of scientists from the physical and the biological sciences. This discussion forum is dedicated to serving this need for interdisciplinary communication.
A wide range of substances are able to catalyze ice nucleation. Various inorganic crystalline solids (the most well known of which is silver iodide), amino acid crystals, monolayers of long chain alcohols and organic compounds such as phloroglucinol and metaldehyde can catalyse the freezing of supercooled water. Substances that are abundant in atmospheric aerosols, such as soot, mineral dusts and metallic particles are also ice nucleation active (INA). In the atmosphere near forests, INA combinations of terpenes and of other tree oils with iodine have been detected. But among all the different ice nucleators naturally present in the environment, biological ice nucleators are among the most active. INA organisms include plants, fungi, bacteria, vertebrates and invertebrates.
Atmosphere physicists have long sought the ice nucleators responsible for various freezing processes in nature. Several decades ago, when INA micro-organisms were detected in atmospheric aerosols and in clouds, biologists joined in the heightened effort to investigate the role of biological ice nucleators in atmospheric processes that require freezing - such as rain formation. Recently there has been renewed interest in the unanswered questions about this role. Assessments of an atmospheric role for biological ice nucleators are gathering momentum as techniques of detection improve, as understanding of biological sources is growing, and as observations and modelling of clouds elucidate the role of early ice nucleation in the formation of precipitation and in determining other cloud characteristics. Progress in understanding the role of biological ice nucleators in these atmospheric processes that define our climate requires close collaboration of scientists from the physical and the biological sciences. This discussion forum is dedicated to serving this need for interdisciplinary communication.
Cindy Morris
French National Agricultural Research Institute (INRA)
Avignon, France
29 Nov. 2008
