Two experiments expand understanding of cloud formation

Ars Technica : A pair of experiments examining cloud formation has revealed that the impact of cosmic rays is likely dwarfed by other factors. Jasper Kirkby of CERN and his colleagues used one of CERN’s accelerators to fire high-energy particles into a controlled environment to observe the rate of creation of ultrafine particulates that could serve as seeds for condensation. They found that nitrogen was unexpectedly present in all the particulates created. So they introduced small amounts of organic nitrogen-carrying molecules, called amines, into the chamber. The rate of particulate formation increased more than a thousand times that seen in earlier experiments. That suggests that amines are a much more significant cause of cloud formation than cosmic rays. Henrik Svensmark of the Danish National Space Institute and his colleagues used a similar chamber with natural cosmic rays to measure the size of the particulates created by ionizing radiation. The researchers expected that introducing a secondary source of ionizing radiation—in this case, radioactive cesium—would increase their size. It did not, but it did confirm the small increase in the number of tiny particulates formed by ionizing radiation.