Those whose memories extend back further than the latest Nobel award may recall that since at least 1960, cosmic rays have been repeatedly invoked as causing cloud formation and thus driving climate change. This conceit has been knocked down innumerable times but keeps arising. While on its face it is reasonable to think that ionization of molecules by cosmic rays will drive formation of small aerosols, there has been very little (and here Eli considerably exaggerates) on the relative importance of ionized aerosols and neutral ones.
Now comes Markku Kulmala, Ilona Riipinen, Mikko Sipilä, Hanna E. Manninen, Tuukka Petäjä, Heikki Junninen, Miikka Dal Maso, Genrik Mordas, Aadu Mirme, Marko Vana, Anne Hirsikko, Lauri Laakso, Roy M. Harrison, Ian Hanson, Carl Leung, Kari E. J. Lehtinen, Veli-Matti Kerminen in Science 318 (5847), 89 - 92 (2007) who have hiked into the Finnish forest sherpaing a large amount of new instrumentation including a Neutral Cluster–Air Ion Spectrometer (NAIS), a UF-02proto Condensation Particle Counter and a Grimm nanoDMA and Faraday Cup Electrometer preceded by a unipolar charger and emerged to write on Toward Direct Measurement of Atmospheric Nucleation.
Atmospheric aerosol formation is known to occur almost all over the world, and the importance of these particles to climate and air quality has been recognized. Although almost all of the processes driving aerosol formation take place below a particle diameter of 3 nanometers, observations cover only larger particles. We introduce an instrumental setup to measure atmospheric concentrations of both neutral and charged nanometer-sized clusters. By applying the instruments in the field, we come to three important conclusions: (i) A pool of numerous neutral clusters in the sub–3 nanometer size range is continuously present; (ii) the processes initiating atmospheric aerosol formation start from particle sizes of 1.5 nanometers; and (iii) neutral nucleation dominates over the ion-induced mechanism, at least in boreal forest conditions.If the rate of cosmic ray driven ionized nuclei formation is much too low to drive aerosol (and thus cloud) formation then cloud formation will not depend on cosmic ray fluxes. This result is from a forest, and will certainly be followed up on
Recently it was suggested that the formation of new atmospheric aerosol particles is connected with the existence of thermodynamically stable 1- to 2-nm clusters, formed in the atmosphere by some nucleation mechanism. From a physical standpoint, two very different cluster types in the sub–3 nm size range can be distinguished: charged (air ions or ion clusters) and neutral species. The existence of atmospheric ion clusters as small as 0.5 to 1 nm in diameter has been known for decades, and measurements with ion spectrometers, such as the Air Ion Spectrometer (AIS) and Balanced Scanning Mobility Analyzer (BSMA), have demonstrated that such clusters are present almost all the time. The production rates of ion clusters are, however, generally too low to explain the observed aerosol-formation rates.In view of the insufficient numbers of ion clusters, the keyto understanding atmospheric aerosol formation is clearly the presence of neutral clusters.