Joined: Thu Jun 26, 2003 10:45 pm
Posts: 21420
Location: Southeastern US
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http://www.newscientist.com/article/mg2 ... imate.htmlAnything that affects cloud formation can in theory affect climate, because clouds can either reflect or trap the sun's heat depending on conditions. Cloud droplets can form only on particles above 50 nanometres. In much of the atmosphere, dust, smoke and sea-spray provide more than enough of these cloud condensation nuclei, or CCNs.
High in the atmosphere, however, such particles are scarce. Here, cloud formation depends partly on trace gases condensing to form particles just 1 nanometre across, which can then grow large enough to act as CCNs.
Kirkby is part of the CLOUD experiment at CERN to investigate whether cosmic rays influence cloud formation. The team started by looking at the formation of the very small particles - a process called aerosol nucleation - by mimicking atmospheric conditions inside an ultraclean steel "cloud chamber", which Kirkby says is the cleanest ever created. Cleanliness is vital since contaminants can themselves become sites of aerosol nucleation.
Aerosol nucleation is known to require sulphuric acid, but Kirkby's team found that it is not enough by itself at low altitudes - the presence of an additional organic trace vapour is needed (Nature, DOI: 10.1038/nature10343). "If there is too little of either component then nucleation will not occur at an appreciable rate in the low atmosphere," says Kirkby. That means the organic component - and thus the role of living organisms - is more important than had been thought, although the full implications are not yet understood.
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