The European Organization for Nuclear Research, CERN, is creating an atmospheric research facility at its particle physics laboratory. Called CLOUD, it will consist of a special cloud chamber exposed to pulses of high-energy particles from one of CERN’s particle accelerators. Conditions prevailing the Earth's atmosphere will be recreated in CLOUD, and the incoming particles will simulate the action of cosmic rays.
The SKY experiment
To investigate the role of cosmic rays in cloud formation low in the Earth’s atmosphere, the SKY experiment used the natural muons, that can penetrate even to the basement of the Danish National Space Center in Copenhagen. The hypothesis is that electrons released in the air by the passing muons promote the formation of molecular clusters, that are building blocks for cloud condensation nuclei.