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).     

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.     

An improved model of the condensation nucleus counter with stereo-photomicrographic recording

Summary A new model of the condensation nucleus counter with stereo-photomicrographic recording is described which is distinguished by perfect symmetry in its construction, reduced turbulence, two separate microscopes with photographic attachments and a novel dark-field illumination which eliminates completely fogging of the graticule even after prolonged use of the instrument. A view-finder microscope permits observations of the graticule so that the instrument can also be used for counting nuclei by eye. When the graticule is removed the droplets can be photographed in space stereoscopically.The use of the counter and its accessories is described and the dimensions and range of the instrument given.

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Zusammenfassung Es wird ein neues Model des Kondensationskernzählers mit stereo-photomikrographischer Registrierung beschrieben, welches sich durch vollkommene Symmetrie der Konstruktion, reduzierte Turbulenz, zwei gesonderte Mikroskope mit photographischen Zusatzeinrichtungen und einer neuartigen Dunkelfeldbeleuchtung auszeichnet, welche das Beschlagen der Zählplatte, selbst nach langem Gebrauche des Instrumentes, völlig eliminiert. Ein Suchermikroskop gestattet die Beobachtung des Zählglases, so dass das Instrument auch als Kernzähler für Augenbeobachtungen gebraucht werden kann. Wenn die Zählplatte entfernt wird, können die Tröpfchen im Raume stereoskopisch photographiert werden.Der Gebrauch des Kernzählers und seines Zugehörs wird beschrieben, sowie die Dimensionen des Instrumentes und der mit ihm mögliche Umfang der Kernzählungen angegeben.

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The research reported in this article has been sponsored and supported in part by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, United States Air Force, under Contract AF 61(052)-26, through the European Office, ARDC in Brussels.     

A small portable photo-electric condensation nucleus counter

Summary A direct-beam photo-electric condensation nucleus counter is described, the height of which is less than one third of that of the photo-electric nucleus counter, School of Cosmic Physics Model 1957 with a corresponding reduction in weight but of approximately the same accuracy as the standard model.It employs an ultra-sensitive Cadmium-Selenide photoconductive raster cell and uses for measuring the extinction in aerosols of low nuclear concentration a simplified electrical compensation method which requires onlyone microammeter. The extinction of aerosols with high concentration is measured in the standard way on the same microammeter with an increased initial setting.A calibration curve of the new counter is given.

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Zusammenfassung Es wird ein photo-elektrischer Kondensations-Kernzähler mit direkter Durchstrahlung des Nebelrohres beschrieben, dessen Höhe weniger als ein Drittel jener des photo-elektrischen Kernzählers Modell 1957 der Schule für kosmische Physik beträgt und dessen Gewicht dem entsprechend reduziert ist. Die Genauigkeit des neuen Instrumentes ist ungefähr die gleiche wie die des Standard Modells.Der kleine Kernzähler benützt eine überempfindliche Cadmium-Selenid Rasterzelle, welche eine Weiterentwicklung der Cadmium-Sulfid-Photowiderstände ist. Die Extinktion von Aerosolen mit kleiner Kernzahl wird mittels einer vereinfachten elektrischen Kompensationsmethode gemessen, welche nurein Mikro-Amperemeter benötigt.Die Extinktion in Aerosolen mit hoher Konzentration wird in der normalen Weise mit demselben Mikro-Amperemeter, aber mit einer vergrösserten Anfangseinstellung gemessen.Die Eichkurve des neuen Kernzählers wird mitgeteilt.

     

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 photo-electric condensation nucleus counter of high precision

Summary A new model of the direct beam photo-electric condensation nucleus counter and its properties are described. The main feature of the construction is the reduction of the fog-tube diameter which resulted in the complete elimination of all uncertainties in the measurement of the light intensity after the fog is formed by adiabatic expansion. —Individual measurements with two identical counters of this design which incorporate all previous improvements, agree to better than 5% in 70% of all cases, their average absolute difference being 2%. Deviations of more than one division of meter readings (or 10% of concentration) were not observed. This agreement is maintained over long periods. — A calibration curve of the latest model of the photo-electric nucleus counter is given.

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Zusammenfassung Es wird ein neues Modell des photo-elektrischen Kernzählers mit direkter Durchstrahlung des Nebelrohres und seine Eigenschaften beschrieben. Das hauptsächliste Merkmal der Konstruktion besteht in der Verkleinerung des Durchmessers des Nebelrohres, durch welche eine vollständige Beseitigung aller Unsicherheit in der Messung der Intensität des Lichtes, nachdem sich der Nebel durch adiabatische Ausdehnung gebildet hat, erzielt wurde. —Einzelmessungen mit zwei identischen Kernzählern dieser Konstruktion, in welcher alle früheren Verbesserungen einverleibt wurden, stimmen besser als 5% in 70% aller Fälle überein, wobei das Mittel der absoluten Differenzen 2% beträgt. Abweichungen von mehr als einem Skalenteil des Mikroamperemeters (oder 10% der Konzentration) wurden nicht beobachtet. Diese Übereinstimmung hält über lange Perioden an. — Es wird eine Eichkurve des neuesten Modells des photo-elektrischen Kernzählers gegeben. Eine umfangreiche Eichtabelle kann von der Meteorologisch-Geophysikalischen Abteilung der Schule für kosmische Physik kostenfrei bezogen werden.

     

An automatic condensation nucleus counter

Summary Samples of air are sucked into a tube, partly lined with damp blotting paper, and become saturated with water vapour. They are then allowed to expand and the cloud which is formed scatters light from a bulb at the side of the tube to a photomultiplier at one end of it. The sampling and expansion are controlled by solenoid valves and the apparatus works continuously, giving readings at intervals of one minute.     

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.     

The precision nucleus counter (Pollak type) with automatic recording

Summary In order to obtain an automatic recording nucleus counter with greater accuracy than that ofVerzár, a precision photoelectric nucleus counter (Pollak type) with ceramic lining and internal diameter 2.5 cm has been substituted for the horizontal fog tube inVerzár's automat. Certain small alterations, have been made to the electric circuit of the recorder. The new arrangement can be easily calibrated and shows an accuracy approaching that of the precision counter operated under optimum conditions.

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Zusammenfassung Um einen automatischen Kondensationskernzähler von grösserer Genauigkeit als es der vonVerzár ist, zur Verfügung zu haben, wurde das horizontale Nebelrohr im Automaten vonVerzár durch einen photo-elektrischer Präzisions-Kernzähler (BauartPollak) mit unglasiertem Porzellanfutter und einem inneren Durchmesser von 2.5 cm ersetzt. An der elektrischen Schaltung der Registriereinrichtung wurden gewisse kleine Änderungen vorgenommen. Die neue Anordnung kann leicht geeicht werden und besitzt eine Genauigkeit, welche jene des Präzisions-Kernzählers unter optimalen Betriebsbedingungen erreicht.

     

Production of atmospheric condensation nuclei by sunrays

Summary 1) It is confirmed that in filtered, nucleus-free air, in a polyethylene balloon, if irradiated by sunglight, an immediate large number of condensation nuclei appear. — 2) The nucleus count rises to about 35. 000/cm³ and if the irradiation is continued does not increase, but decreases. This decreased is accelerated in the dark. — 3) Less intensive sunlight as when the sun was covered by clouds, gives slower and smaller increases. — 4) The same was observed if, instead of air, inducstrial oxygen or nitrogen was used. — 5) Traces of H₂S increase the sun effect enormously. — 6) Traces of NH₃ also increase it, but less than H₂S. — 7) SO₂ filtered through cottonwool gave also in the dark nuclei, which then decreased in number. — 8) It is supposed that H₂S is oxydized by the photochemical action of the sun's visible spectrum to SO₂ SO₃ SO₄ which is a nucleus. With NH₃ the formation of (NH₃)₂ SO₄ is probable. But no direct proof is given that these are the actual impurities which explain the sun's action on air. It is calculated that dilutions of 10^–15 of an impurity of the type of H₂S can quantitatively explain the sun effect. — 9) The work ofAitken is extensively quoted, who noticed, 50 years ago, the «fog produced by sun».

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Zusammenfassung 1) Es wird bestätigt, dass Sonnen-Bestrahlung von filtrierter kernfreier Luft, welche in einem Polyethylen-Ballon aufbewahrt ist, zum Entstehen einer hohen Zahl von Kondensations Kernen führt. — 2) Die Kernzahl steigt auf etwa 35 000/cm³. Wird die Bestrahlung fortgesetzt, dann steigt sie nicht weiter sondern nimmt ab. Die Abnahme wird im Dunkeln beschleunigt. — 3) Durch Wolken abgeschwächtes Sonnenlicht gibt eine langsamere, weniger grosse Kernbildung. — 4) Dieselben Beobachtungen wurden mit industriellem Sauerstroff und Stickstoff auch gemacht. — 5) Spuren von H₂S verstärken den Sonneneffekt enorm. — 6) Spuren von NH₃ verstärken ihn auch, jedoch weniger. — 7) SO₂ Gas, gefiltert durch Baumwollfilter giebt auch im Dunkeln schon Kerne, deren Zahl dann wieder abnimmt. — 8) Es wird angenommen, das H₂S durch photochemische Wirkung des sichtbaren Sonnenlichtes oxidiert wird zu SO₂ SO₃ SO₄ welch letzteres bereits als H₂HO₄ ein Kondensationskern ist. Mit NH₃)₂ SO₄ Kondensationskerne gebildet werden. Es sind jedoch keine direkten Beweise dafür vorhanden, dass diese Gase die Verunreinigungen der atmosphärischen Luft sind, welche den Sonnenffekt geben. Es wird aber berechnet, dass schon Verdünnungen von 10^–15 eine Verunreinigung H₂S den Sonnen-Effekt erklären. — 9)Aitken's Werk, der bereits vor 50 Jahren von « durch Sonne verursachten Nebel « sprach, wird gewürdigt.

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From the Clima-physiological Laboratory of St. Moritz-Bad.     

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».     

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.     

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.

     

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.     

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.

     

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     

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:

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   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.     
   
   

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.