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...
The formation of aerosols in a gaseous mixture of water and sulfuric acid was studied experimentally. The formation of particles having been demonstrated during previous experiments, an experimental device was developed which would make it possible to determine the rate of nucleation for different values of partial pressure of water vapor and sulfuric acid. These results were compared with the numerical values given by Mirabel and Katz on the one hand, and by Kiang and Stauffer on the other hand; it was found that the most satisfactory correlation is obtained when the value of 3.5×10−4 torr is adopted for the pressure of the sulfuric acid saturating vapor at a temperature of 20 °C.
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