Production of atmospheric condensation nuclei by solar radiation

Summary Air with a very low count of atmospheric condensation nuclei was irradiated by direct sunlight through an uviol glass window, or through ordinary glass or in a polyethylene balloon. The nucleus count rises immediately and reaches very high values.

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Zusammenfassung Luft mit sehr niedriger Zahl von atmosphärischen Kondensations-Kernen wurde mit direktem Sonnenlicht bestrahlt, entweder durch ein UV Glas oder durch gewöhnliches Glas oder durch einen Polyethylen-Ballon. Die Zahl der atmosphärischen Kondensations-Kerne steigt sogleich und erreicht sehr hohe Werte.

     

The nuclei of atmospheric condensation

Summary Our present knowledge concerning the abundance, size, physical properties, origin and nature of condensation nuclei is reviewed and critically assessed.     

Influence of sunlight on atmospheric condensation nuclei

I has been shown that irradiation of air by sun-rays leads to a formation of atmospheric condensation nuclei, as measured with the automatic nucleus counter (1).To control the influence of the material, experiments were done in a gasometer where a rubber balloon was built in, also in a metal container covered either with uviol glass or window glass, or with air in a polyethylene balloon. The same influence of sunrays was observed in each case.Similar experiments were then done with compressed air from a metal container, or with oxygen gas, nitrogen gas or nitrous oxide all from metal containers. In all cases sun-rays produced condensation nuclei; the effect was present both at 1800 m and at 270 m altitude. Diffuse sunlight with high clouds also had an effect. Infra-red radiation and mechanical shaking were without result, but ultraviolet rays from a quartz-mercury lamp increased the nucleus count of the balloon whether it contained air or one of the above-mentioned gases.As yet it has not been possible to decide the mechanism of formation of these nuclei and what their meteorological and biological role might be.The detailed paper will appear later in «Geofisica pura e applicata».     

The effects of condensation nuclei in atmospheric electricity

Summary The effects of condensation nuclei in the atmosphere are discussed, particularly in relation to the «sunrise effect» and it is shown that the introduction of positively charged nuclei is the only process yet suggested that can explain the observed results.     

Uncharged condensation nuclei produced by ultra-violet light

Summary A large number of experiments have been carried out with the object of determining the nature, properties and source of the condensation nuclei produced by the action of a beam of ultra-violet light within an expansion chamber. This paper is essentially a qualitative summary of the results which have been obtained. It is concluded that these experiments show that it is the rubber component of the chambers that has been responsible for the major part of the effect. It is by no means suggested that this is the only source of the nuclei, but it is implied that only apparatus free from rubber should be used in any study of the properties of the nuclei associated with a given gas or vapour.Work ofA. J. Barnard (now at University of Natal, Pietermaritzburg) andJ. R. Atkinson.     

The condensation nuclei produced by point discharge

Summary The properties of condensation nuclei generated at a metal point corona discharge have been examined. The threshold voltages for nucleus production and for small ion production are the same. The fraction of the nuclei which is charged is initially small and becomes virtually zero after a few seconds. It is demonstrated that in the non-uniform field near the point there is a force on the nuclei driving them to the point. From determinations of the diffusion coefficient it is tentatively concluded that a portion at least of the nuclei are originally of molecular size. No satisfactory explanation has been found for certain anomalous features of the variations in size and in concentration of the nuclei with time after production.

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Zusammenfassung Es wurden die Eigenschaften von Kondensationskernen untersucht, die durch Koronaentladung von einer Metallspitze erzeugt wurden. Die Spannungsschwelle für die Erzeugung von Kondensationskernen und kleinen Ionen ist die gleiche. Der Bruchteil der Kerne, welche geladen sind, ist anfangs klein und wird nach einigen Sekunden praktisch null. Es wird gezeigt, dass in dem inhomogenen Felde nahe der Spitze eine Kraft auf die Kerne wirkt, welche sie zur Spitze treibt. Aus Bestimmungen des Diffusionskoeffizienten wird versuchsweise geschlossen, dass wenigstens ein Teil der Kerne ursprünglich molekulare Grösse hat. Keine befriedigende Erklärung für gewisse anomale Eigenschaften der zeitlichen Änderungen der Grösse und Konzentration der Kerne nach ihrer Erzeugung wurde gefunden.

     

The generation of condensation nuclei by ionising radiation

Summary The production of condensation nuclei by the irradiation of filtered nuclei-free air by X-rays, alpha particles and beta particles is described. It is found that nuclei are created in large numbers by such irradiation and that there appears to be a threshold radiation dose at which the nucleus concentration is increased by a factor of more than a hundred.The effect of varying sulphur dioxide content of the irradiated air has been investigated and for concentrations of between one and ten milligrams per cubic metre of air there is some proportionality between the sulphur dioxide content of the air and the nucleus concentration produced by a given radiation dose.It is shown, however, that sulphur dioxide cannot be exclusively responsible for the generation of condensation nuclei by irradiation of filtered air and other possible agents and mechanisms are suggested.     

The relation between the concentration of atmospheric condensation nuclei and other meteorological elements at valentia observatory

Summary Measurements of the concentration of condensation nuclei made twice daily (0h and 12h GMT) with aNolan-Pollak photo-electric counter at Valentia Observatory, in the extreme Southwest of Ireland, over the 4 years 1951–1954, are analysed to show relation with other meteorological elements. It is found that concentration at 12h is generally higher than at (h and that precipitation at the time of observation or in the preceding hour reduces concentration by between 40% and 50%. From measurements made when there was no precipitation at the time or in the previous hour it is found that concentration decreases with increasing wind speed but does not vary appreciably with wind direction apart from a sector from which pollution could be expected. High concentrations are found with visibility below 7 miles, with inversion of temperature, when free from the effects of pollution, follows fairly closely that of duration of bright sunshine.

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Zusammenfassung Es werden Messungen der Konzentration von Kondensationskernen, welche zweimal täglich (um 0 ^h und 12 ^h G.M.T.) mit einem photo-elektrischen Kernzähler nachNolan undPollak am Observatorium in Valentia (im äussersten Südwesten von Irland) in den Jahren 1951 bis 1954 durchgeführt wurden, auf Beziehungen zu anderen meteorologischen Elementen hin untersucht. Die Resultate zeigen, dass die Konzentration um 12 Uhr im allgemeinen grösser ist als um 0 Uhr und, dass die Niederschlag zur Zeit der Beobachtung oder in der der Beobachtung vorausgehenden Stunde die Konzentration um 40 bis 50% herabsetzt. Wenn kein Niederschlag zur Zeit der Messung oder in der vorangehenden Stunde verzeichnet wurde, nimmt die Konzentration mit zunehmender Windgeschwindigkeit ab; sie ändert sich jedoch nicht nennenswert mit der Windrichtung, abgesehen von einem Sektor, aus welchem Verunreinigung zu erwarten war. Hohe Konzentration wurde bei Sichtweiten unterhalb 7 Meilen gefunden, ferner bei Temperaturinversion, und, um 12 Uhr, bei geringer Bewölkung. Der jährliche Gang der Konzentration der Kerne folgt ziemlich genau jenem der Sonnenscheindauer, wenn die Fälle, wo Verunreinigung der Luft stattfindet, ausgeschlossen werden.

     

An ionometric counter for condensation nuclei

Summary Condensation nuclei detectable in the range of supersaturation used in the expansion method do not play the role expected earlier, for the production of water droplets in natural clouds.However, these nuclei exist in the atmosphere, and they can be of importance in other processes in the air; for example, they can be partners for annihilation of small air ions there. Therefore, a direct investigation of the interaction between the condensation nuclei and the small air ions may be of interest. For this purpose an, ionometric counter for condensation nuclei is designed, in which the air under examination is mixed in a mixing chamber with small air ions produced by a tritium ion-generator, and the presence of condensation nuclei is measured by the decrease of the concentration of air ions recorded with an aspiration ion counter as compared to the concentration recorded when filtered air was originally sucked through the mixing chamber.Comparatively rapid variations of the concentration of nuclei can be continuously recorded. The electrical properties of the aerosol particles destroying air ions can be investigated by inserting an electrical filter. By the ionometric counter condensation nuclei can be investigated without adding water particles to them.     

A continuous recorder for condensation nuclei

Summary A continuous recorder of condensation nuclei with multiple ranges that are substantially linear over the range of 500 to 50,000 nuclei per ml full scale is described. The range can be extended but the scale law becomes proportional to the cube root of the nuclei concentration. The sampling rate is 100 ml/sec and the response time is less than 2 seconds.The unit works on fog-scattered light with dark-field illumination. The expansion ratio is adjustable (at the expense of recalibration) and can be made high enough to respond to a radium source. The electronics are simple and sturdy; the unit has been used on a truck in motion.     

A condensation nuclei counter with photographic recording

Summary A condensation nuclei counter based onAitken's principle is described and depicted. It permits simultaneous observations of the graticule by two persons or the observation of the graticule by one person and the synchroeous photographic recording of the droplets on 35 mm film strip or single plates. With one exposure, the droplets on 24 squares of the millimetre graticule can be recorded so that a repetition of the necessary operations required by other counters in order to obtain an average count becomes superfluous and the time taken for one experiment is reduced to three quarters of a minute. The limitation to five droplets per square mm recommended for all hitherto existing nuclei counters with eye observations is removed when the droplets and the graticule are photographed. By the use of a special sealing arrangement and by employment of vacuum taps which proved most satisfactory with the previous construction of a photo-electric nuclei counter, leakages are practically impossible. The glass windows of the receiver are interchangeable with plates of conducting glass which can be heated by the passage of an electric current. The construction ensures that the 1 cm distance above the graticule is always maintained, independent of the tightening of the sealing arrangement. The receiver is equipped with a stirrer operated from outside by a permanent magnet. Two easily detached pumps are provided; one for purifying the air in the receiver and for the dilatation, the other for sucking the sample of impure air into the receiver. The adiabatic cooling in the receiver can be produced e. g. by means of an expansion pump. The method of measuring is discussed. Examples of records are reproduced. Applications and the development of a fully automatic recording nuclei counter are indicated.

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Zusammenfassung Ein Kernzähler, derAitkens Prinzip benützt, wird beschrieben und abgebildet. Er gestattet die gleichzeitige Beobachtung des Zählglases durch zwei Personen oder die Beobachtung des Zählglases durch eine Person und die gleichzeitige photographische Registrierung der Tröpfchen auf Kino-Normalfilm (von 35 mm) oder Platten. Miteiner Aufnahme können die Tröpfchen auf 24 Quadraten des in Quadratmillimeter geteilten Zählglases festgehalten werden, so dass eine Wiederholung der erforderlichen Operationen, welche bei allen anderen Kernzählern vorgeschrieben sind, um Mittelwerte der Einselzählungen zu erhalten, überflüssig ist und die Dauereines vollständigen Experimentes auf dreiviertel Minuten reduziert wird. Die Beschränkung auf fünf Tröpfchen per Quadratmillimeter, welche für die meisten bisherigen Kernzähler bei Augenbeobachtungen empfohlen wird, wird aufgehoben, wenn die Tröpfchen und das Zählglas photographiert werden. Durch eine spezielle Dichtungseinrichtung und durch Verwendung von Vakuum-Hähnen, welche sich bei der Konstruktion eines photo-elektrischen Kernzählers so sehr bewährt haben, ist Undichtwerden des Rezipienten praktisch unmöglich. Die Spiegelglasfenster des Rezipienten können gegen solche aus leitendem Glas ausgetauscht werden, welche mittels eines durch sie geschickten elektrischen Stromes geheizt werden können. Die Konstruktion gewährleistet, dass der Abstand (1 cm) oberhalb des Zählglases stets erhalten bleibt, unabhängig vom Drucke, der auf die Dichtung ausgeübt wird. Der Rezipient ist mit einem Rührer ausgestattet, der von aussen durch einen permanenten Magneten betätigt wird. Es sind zwei Pumpen vorgesehen, die leicht abnomontiert werden können; die eine ist für die Reinigung der Luft im Rezipienten und für die Dilatation zur Herbeiführung des Tropfenfalles bestimmt, die andere dient zum Einsaugen der zu untersuchenden Luftprobe in den Rezipienten. Die adiabatische Abkühlung im Rezipienten kann z.B. mittels der Dilatationspumpe erzeugt werden. Die Messmethode wird beschrieben. Probe von photographischen Registrierungen der Tröpfchen auf dem Zählglase werden reproduziert. Einige Anwendungen und die Entwicklung eines voll-automatisch registrierenden Kernzählers wird angedeutet.

     

On some measurements of the condensation of different vapors upon Aitken condensation nuclei

No final theory on the activity of Aitken nuclei has been established yet. In particular the supersaturation is not known for the Aitken nuclei to grow into droplets, f.e. according toF. Volz only nuclei of radius >0.1 can cause condensation under atmospheric conditions. On the other hand according toH. G. Müller condensation over the continents has to occur at the Aitken nuclei since precipitation washes out the other nuclei.This uncertainty becomes obvious in the interpretation of the experimental results.Chr. Junge found that the necessary activation supersaturation of a continental Aitken aerosol and of artificial aerosols of the same size of nuclei lies between 2 and 20%, 10% being sufficient for the main fraction of nuclei to grow.In contrastW. Wieland was able to activate in a mixing cloud chamber a big portion, if not all, of the nuclei of a continental aerosol at supersaturations below 1.5%. Some of our own results, obtained with the same technic, agree with this. At supersaturations below 0.8% at least half of the Aitken nuclei present are activated. To obtain the same result with benzene and acetone we found, that benzene required a slightly smaller, and acetone a somewhat bigger supersaturation.However later experiments revealed a considerable effect of the geometry of the mixing cloud chamber upon the results. Since the physics of the chamber has not been fully explored the method was abandoned. Instead the principle of cooling by adiabatic expansion was used. An expansion apparatus based on the principle of a fotoelectric nucleus counter was developed allowing us to measure with two cathode ray oscillographs the pressure and simultaneously the change of intensity of a lightbeam due to the scattering on the forming cloud as a function of time. The length of the lightbeam could be chosen between 60 and 200 cm. The overpressure before the expansion was always 180 mm of mercury. The ratio of expansion rates was 12.53060 at the beginning of the expansion. The slowest rate was about 6 seconds, corresponding to a rate of ascent of 210 m/s at the beginning of the expansion. Smaller rates could not be obtained because of heat transfer at the chamber walls.The present work has been performed for the Eidgenössische Kommission zum Studium der Hagelbildung und der Hagelabwehr (Switzerland) at the research station Osservatorio Ticinese Locarno-Monti della Centrale Meteorologica Svizzera     

On condensation nuclei produced at heated surfaces

Summary An investigation of heated surfaces of glass, metal and oil as sources of condensation nuclei is reported. Below a certain transition temperature the nucleus production is of a temporary nature and decreases to zero with the continued heating of the surface. Above this temperature, however, the nucleus production does not change with time. The transition temperature varies with the material of the surface and is not always associated with the onset of incandescence. The nuclei produced at the lower temperatures have a radius of about 10^–5 cm and, on production, are mainly uncharged. Electric light bulbs can produce appreciable numbers of these nuclei.

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Zusammenfassung Es wird über eine Untersuchung von geheizten Glas-, Metall-und Öloberflächen als Quelle von Kondensationskernen berichtet. Unterhalb einer gewissen Übergangstemperatur ist die Kernerzeugung unbeständig und sinkt bei fortgesetzter Heizung der Oberfläche auf null. Oberhalb dieser Temperatur ändert sich die Kernproduktion nicht mit der Zeit. Es wurde gefunden, dass sich die Übergangstemperatur mit dem Material der Oberfläche ändert und nicht immer mit dem Beginn des Glühens assoziiert ist. Die Kerne, welche bei den niedrigeren Temperaturen erzeugt werden, haben einen mittleren Radius von ungefähr 10^–5 cm und sind bei ihrem Entstehen grösstenteils ungeladen. Elektrische Glühlampenkönnen eine beträchtliche Zahl dieser Kerne erzeugen.

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Note: The research reported in this document has been sponsored in part by the Office, Chief of Research and Development, U.S. Department of Army, through its European Office under Contract No. DA-91-508-EUC-194.     

Vertical profiles of condensation nuclei in the stratosphere

An automatic condensation nuclei counter was developed for the concentration range of about 1 to 400 particles per cubic centimeter. After expansion, the water droplets are photographed when they are still suspended in the air so that the counter can be considered an absolute one. The volume in which the droplets are counted is determined by the size of the picture of the droplets as a function of their distance from the focal plane. To eliminate any effect of decreasing pressure with altitude, the cloud chamber is filled with clean air prior to expansion to about half an atmosphere above ambient pressure. This counter was used to obtain vertical profiles of condensation nuclei up to altitudes of 27 km with high altitude balloons. A total of seven profiles was obtained over a period of about one year at 47° N over the United States. Because of the restrictions in the range of the meter no data could be obtained below 5 km. The profiles show the following main features:

1. 1.
   Although there are pronounced fluctuations in the individual flights the average nuclei concentration of 200 to 300/cm³ remains fairly constant from 5 km to the tropopause.     
   
   

A new condensation nuclei counter with continuous oversaturation

Summary By mixing atmospheric air, saturated water vapour and hydrochloric acid a water vapour supersaturation corresponding to that in theScholz-nucleus counter is formed. The density of the fog formed is reproducibly related to the number of condensation nuclei per cm³ and can easily be measured by photocells.

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Zusammenfassung Durch Mischung von atmosphärischer Luft, gesättigtem Wasserdampf und Chlorwasserstoff entsteht eine demScholz'schen Kernzähler entsprechende Wasserdampfübersättigung. Die Dichte des entstehenden Nebels steht in reproduzierbarem Zusammenhang mit der Kondensationskernzahl pro cm³ und kann leicht mittels Fotozellen gemessen werden.

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Presented by Dozent Dr. Ing.R Mühleisen, Max-Planck-Institut für Physik der Stratosphäre,Weissenau bei Ravensburg (Federal Republic of Germany).     

Role of condensation nuclei as carriers of radioactive particles

Summary The effect on the deposition of thoron and radon decay products of attachment to condensation nuclei is described. Methods are suggested of using these decay products as markers for condensation nuclei and comparison is made between radioactive and non radioactive determinations of the diffusion coefficients of marked nuclei. The spontaneous production of condensation nuclei by irradiation of clean air by alpha and beta particles and by X-rays is described.     

On the condensation nuclei about the time of sunrise

Summary Some marked variations of the content of condensation nuclei in the air deserve to be considered individually. it is shown that by simultaneous measurements of phenomena other condensation nuclei, especially atmospheric electrical, a more complete insight into all the processes involved could be obtained, when investigating the condensation nuclei during the time about sunrise.

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Zusammenfassung Einzelne ausgeprägte Variationen des Gehaltes an Kondensantionskernen in der Luft verdienen individuell behandelt zu werden. Es wird gezeigt, dass mit gleichzeitig ausgeführten Messungen anderer, besonders luftelektrischer Erscheinungen, neben jenen der Kondensationskerne eine vollständigere Einsicht in alle in Betracht kommenden Prozesse erhalten wird, wenn die Kondensationskerne vor und nach dem Sonnenaufgang untersucht werden.