Formation and evolution of nuclei of condensation that appear in air initially free of aerosols

Abstract

The formation of nuclei of condensation in air initially cleansed of aerosol particles by filtration has been investigated. Such oeormation may be achieved in the dark. The oeormation process is accelerated by the action ooe sunlight or by the introduction into the chamber ooe thoron oeree oerom active deposit. The evolution ooe these particles in time, as well as their state of charge, has been studied, and an important influence ooe coagulation on the process has been found. The possible role ooe such particles as regards the origin and behavior ooe the properties ooe natural aerosols must be considered. FORMATION IN THE DARKBillard e• al. [1968] used a spherical Plexiglass chamber with an 800-liter capacity, which could be kept in the dark or be exposed to sunlight at will. The chamber was filled by air drawn from the outside that had been freed of aerosol particles by filtration through the initial circuit shown in Figure 1. By means of a second circuit, Billard et al. derived information about the air filling the sphere by sampling it using a ?ollak nuclei-of-condensation counter. With this counter the number of particles whose minimum radius is of the order of 10 -7 cm can be counted. The concentrations of particles measured in this fashion are comparable to a relative precision of the order of 10%.Figure 2, curve 1, sh. ows as a function of time the variation of concentrations of nuclei that appear in the darkened system. These nuclei begin to be detectable about 10 minutes after filtration. This delay is doubtless due to the fact that the nuclei less than about 10 -7 cm in radii, which first appear, escape detection in the counter.Despite the inaccuracy of the counter and the uncertainties surrounding the minimum radius of the nuclei that are detected, the results that follow are sufficiently clear to merit presentation. One notes that the concentration increases, passes through a maximum in about 30 minutes, and then declines quite slowly. The maximum, which is subject to considerable fluctuation, lies between some hundreds and 5 X 104 nuclei cm -•. It results unquestionably from the impurities initially present in the air drawn into the chamber from outside. At the end of 7 hours, a sample of air containing at the maximam 3 X 104 nuclei cm -3 has no more than 200 nuclei cm -• remaining. This density approximately represents the background noise of the counter. Figure 3 shows a set of curves obtained under the same conditions on different occasions with samples of outside air more or less contaminated by impurities.It has been established in working with chambers of different substances (glass, Plexiglass, etc.) that the nature of the walls has no influence on the rate of production of nuclei and the rate is the same even if one increases the temperature of the equipment by twenty degrees centigrade.The events described here are only observed i• the air studied, in the region o/Paris, has been collected in •ull daylight. No appreciable formation is observed if the air is collected at night. ACTION OF LI...

Tropospheric New Particle Formation and the Role of Ions

“…In the twentieth century, laboratory studies have confirmed Wilson's initial experiments (e.g. Bricard et al 1968;Vohra et al 1969;Raes and Janssens 1985), but research on atmospheric particle formation from ions has intensified only in the dawn of the twenty-first century with the heightened awareness of the relevance of new particle formation from the gas phase, which can significantly increase concentrations of aerosol particles and cloud condensation nuclei in the troposphere , and thereby establishes a connection between atmospheric chemical composition, aerosols, clouds, and climate. Interest for the topic was also fueled by the possibility that the solar cycle modulation of atmospheric ionization through galactic cosmic rays could give rise to a similar modulation in aerosol and cloud droplet concentrations, and provide a mechanism to explain reported correlations between the decadal solar cycle and tropospheric observables, such as cloud cover (Svensmark and Friis-Christensen 1997;Marsh and Svensmark 2000;Carslaw et al 2002;Harrison and Carslaw 2003).…”

Results from the CERN pilot CLOUD experiment

“…Concerning the effects of cosmic rays on aerosols, early studies (Bricard et al, 1968;Vohra et al, 1984) have demonstrated ultrafine particle production from ions in the laboratory, at ion production rates typically found in the lower atmosphere; this has also been found in more recent laboratory experiments under conditions closer to those found in the atmosphere (Svensmark et al, 2007;. Observations of ion-induced nucleation in the atmosphere have also been reported (Eickhorn et al, 2002;Lee et al, 2003).…”

The role of atmospheric ions in aerosol nucleation – a review

“…A correlation of particle number with SO 2 was also reported. Bricard et al (1968) reported a similar effect in an experiment where the charged fraction of the detectable particles (>100 nm) was measured by applying an electrical charge to a metal tube placed prior to the particle counter, thus removing charged particles. It was shown that a measureable charged fraction only appeared about 50 min after the injection of 220 Rn.…”

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