Photo-electric Nucleus Counter Research Articles

Aerosol climatology measurements with a Nolan-Pollak counter

Abstract The Nolan-Pollak photoelectric nucleus counter was originally developed in the 1940s for aerosol climatology measurements although its versatility led subsequently to many other applications in aerosol science. It has been widely used in manual, automatic and modified forms in many parts of the world to record ambient concentraions of Aitken nuclei. The design, calibration and performance of an automatic counter is described. Measurements of Aitken nuclei at Mace Head, Ireland, are used to discuss its suitability for the purpose of aerosol climatology.

Photo electric nucleus counters for aerosol climatology

Photo electric nucleus counters are used as aerosol detectors at several observatories which are attempting to establish aerosol climatologies. The photo electric nucleus counter has an advantage over absolute nucleus counters in such applications, as it produces a nearly instantaneous “snap shot” of the integrated aerosol concentration in a relatively large volume of air. The Pollak—Nolan type of photo electric nucleus counter is most frequently used in determining the aerosol concentration at these climatological observatories. Laboratory and field experiments indicate that the response of this instrument is extremely repeatable, even though questions may exist relative to its absolute calibration and the minimum size of particles it detects. The repeatability is sufficiently reliable to permit use of existing data if a more precise calibration is accomplished in the future. Many components used in construction of replicas of the Pollak—Nolan counter have become difficult to obtain. A transfer of Pollak's calibration to a geometric replica of this instrument, using more modern components would insure continuance of high quality climatic aerosol data.

Seasonal and Frontal Variation in Antarctic Aerosol Concentrations

Abstract Total aerosol concentrations have been observed twice daily at the South Pole since January 1974, using a Pollak photoelectric nucleus counter. The aerosol size distribution has been approximated using the Rich diffuser denuder and Spurny membrane filter techniques. These observations show the seasonal variation in aerosol concentration at the surface to be of large relative amplitude. The concentrations reach a very low value, with monthly averages of less than 15 cm−3, beneath the strong nocturnal inversion in winter. The mean concentration begins to rise near the time of astronomical sunrise, and attains monthly average values of 100–200 cm−3 during summer months. Variations in aerosol concentration and size accompany meteorological events. Extreme sky clarity and subsequent lowering of temperature and strengthening of the near-surface inversion in winter months are accompanied by nearly unmeasurable aerosol concentrations of 3–5 cm−3; winter warming is sometimes accompanied by increases in ae...

A Portable, Photo-Recording Aitken Counter

Abstract A modern replica of the Aitken counter for detection of aerosol particles smaller in diameter than a half wavelength of visible light has been constructed using modern materials. The instrument employs photographic recording, rather than visual observations, of the cloud drops formed on these particles. This feature eliminates observer bias and provides a permanent record of the observation. Comparison of this instrument with a Pollak photoelectric nucleus counter indicated correspondence in the concentration sensed to well within experimental sampling error.

A Portable Aerosol Detector of High Sensitivity

A portable photoelectric nucleus counter, with similar sensitivity to the Pollak photoelectric nucleus counter with convergent light beam, has been developed and calibrated. This instrument has been incorporated into a packaged measurement system which allows the experimenter to determine the effective diffusion coefficient and fraction charged, of the natural aerosol, in uncontaminated areas. The photoelectric counter has comparable accuracy to the absolute (Aitken, Scholz) counters in the concentration range of interest, and is capable of determining the concentration once per minute.Field tests of the prototype instrument were conducted near sea level in Greenland. The concentration of natural aerosol in this area ranged from 150 to 200 particles cm−3. The instrumentation had sufficient sensitivity to detect a gradual increase in particle size at this low concentration.

A condensation nucleus counter with automatic cycling and digital recording

Apparatus for the automatic recording of the concentration of submicrometre particles in air is described. The system employs the 1946 pattern of the Pollak photoelectric condensation nucleus counter, and is designed so that this instrument is operated in accordance with original calibration data. The operational cycle is controlled by a mechanical timer, and data are recorded by digital equipment in a form suitable for automatic computation of nucleus concentration. Intercalibration data for two similar counters compare favourably with earlier published work, and the system has proved accurate and reliable for over 1000 hours sampling in atmospheric experiments.

Absolute calibration of a photoelectric condensation nucleus counter at low values of nucleus concentration

A new absolute condensation nucleus counter was constructed to investigate the accuracy of the calibration widely used with the Pollak-Nolan photoelectric condensation nucleus counter. An attempt was made to standardize the conditions affecting calibration and, using the new counter, to recalibrate the photoelectric counter at values of extinction less than 16%.

The evaluation of the performance of an electrostatic precipitator using a Pollak-Nolan nucleus counter

The performance of an electrostatic precipitator for aerosol sampling was studied experimentally using a Pollak-Nolan photo-electric nucleus counter. Particles of various sizes lying between 1.4–9.6 × 10 −6 cm were investigated. The aerosols were polydisperse. Special attention was given to finding out the fraction of particles in an aerosol which were charged while passing through the precipitator at various flow-rates. The efficiency of the precipitator was measured at different flow-rates for particles of several sizes. It was shown that there was a bias in favour of both small and large particles when sampling a heterogeneous aerosol with the aid of the precipitator. The results were shown to be independent of the original charged condition of the aerosol entering the precipitator and also of the concentration of nuclei in the aerosol. Oversampling by such a precipitator of both the largest and smallest particles present would render it unsuitable for use on the size-frequency analysis of a heterogeneous aerosol by electron microscopy.

Anomalies in measurements made with a Pollak-Nolan photo-electric nucleus counter

The decay curves of storedAitken nuclei as measured with a photo-electric nucleus counter exhibit small non-random divergencies from the theoretical pattern for these curves. Investigations of these anomalies reveal that their origin is to be found in the counter itself. This is shown to be due to a gradual drying out of the counter, together with a possible cooling due to frequent use. Suggestions for the use of the counter which should eliminate these peculiarities in behaviour are put forward.

The evaluation of the results of a proposed precipitation method particle size spectrometer

A description is given of an attempt to adapt a Pollak-Nolan photo-electric nucleus counter for the purpose of obtaining a general picture of the size frequency distribution of an aerosol of Aitken nuclei. The principle of the method is that of differential evaporation of the large and small water droplets formed at an expansion on different sized nuclei in the counter. A number of features of fog decay in a counter, which militate against the success of the method, are recorded. The results obtained with the spectrometer are discussed in the light of the difficulties encountered.

A condensation method particle size spectrometer

A condensation method of measuring the size frequency distribution of Aitken nuclei is described. Making use of thePollak-Nolan photoelectric nucleus counter it is based on the removal of the nuclei activated at various overpressures from the counter by precipitation and the counting of those that remain. Various stored aerosols are investigated by means of it and the decay mechanisms of these aerosols discussed in the light of the results obtained. The value of the exhaustion method of finding diffusion coefficients is also examined.

A small portable photo-electric condensation nucleus counter

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.

Extinction in a photo-electric nucleus counter using adiabatic expansion of 1.21 pressure ratio achieved by increasing or decreasing the original pressure

Comparisons were made of the extinctions as measured with a photoelectric condensation nucleus counter, Dublin School of Cosmic Physics Model 1957, when the «over-pressure method» or the «under-pressure method» with equal pressure expansion ratios were used for producing the adiabatic cooling of the sample in, the fogtube of the counter. Due to theSchlarb effect the extinction measured by the second method is smaller than that by the first. Tables and graphs for converting the extinction obtained by one method into that by the other are given. The advantages of the underpressure method are given and discussed.

Condensation nuclei and meteorological factors at Giza, Egypt

Measurements of the concentration of condensation nuclei, carried out, daily, every two hours with aNolan-Pollak photoelectric nucleus counter in the period 1957–1960, are analysed for the relation between the concentration and the meteorological elements. It was found that the concentration of condensation nuclei changes according to the following behaviour: 1) The concentration increases to a maximum at:a) relative humidity in the range 50–59%,b) temperature in the range 25.0–29.0°C,c) vapour pressure in the range 12.0–12.6 mm Hg. 2) The concentration increases with direct sun light and decreases with diffused light. 3) The concentration is low during calm weather, high wind speeds and wind directions S-SSW. 4) The concentration varies slightly with the form and amount of clouds present in the sky except the case in which all the sky is hidden.

A diffusion battery without end-pieces or connecting tubing

An account is given of a new instrument for determining the apparent diffusion coefficient of aerosols using the dynamic method in which a diffusion battery without end-pieces or connecting tubing is built into the fog-tube of a photo-electric condensation nucleus counter.

On the scintillation effect in photo-electric nucleus counters

The «scintillation effect» occuring in photo-electric nucleus counters is explained as follows: After an adiabatic expansion a radial temperature distribution is formed in the fog-tube to which corresponds an opposite radial distribution of the refraction index of air. This causes a deflection of the light beam in the direction of the large optical density, giving as a result the changes of the photo-current. A calculation following this idea yields the right order of magnitude and the time dependence of the effect.

New calibration of photo-electric nucleus counters

A new calibration of the improved version of a photo-electric nucleus counter with a fog-tube of 3.85 cm air-column diameter and blotting-paper lining and of a photo-electric counter Model 1957 with air-column diameter of 2.5 cm and ceramic lining was carried out by adjusting the calibration curve of 1946 with reference to the considerably improved absolute (Aitken type) counter with stereophotomicrographic recording.

Further investigations of the fog in the photo-electric condensation nucleus counter

The effect on extinction of isothermal distillation, shrinking of the droplets by evaporation without recondensation of the liberated water vapour, coagulation and differential settling of the fog droplets which take place in the fog of a photo-electric nucleus counter and which can produce a small additional extinction («creep») in the first seconds after its formation, were numerically examined. The relative contribution of each process to the total creep observed is assessed. It is found that isothermal distillation can produce amounts of creep (up to 1.70%) which exceed considerably those caused by evaporation or coagulation. The results of these computations explain the occurrence of creep with concentrations greater than approx. 25 000 nuclei/cm3 in fog-tubes of 3.85 cm air-column diameter.

The precision nucleus counter (Pollak type) with automatic recording

In order to obtain an automatic recording nucleus counter with greater accuracy than that ofVerzar, a precision photoelectric nucleus counter (Pollak type) with ceramic lining and internal diameter 2.5 cm has been substituted for the horizontal fog tube inVerzar'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.

The fog in the photo-electric nucleus counter

The paper deals with some of those properties of the fog in the photo-electric condensation nucleus counter which affect the measurement of its extinction used as an index of nuclei concentration.