E. F. CHEKHOVA

COUNTING

THE NUMBER OF IONS IN THE ATMOSPHERE

at the Meteorological Station

of the Siberian Technological Institute

in Tomsk in the summer of 1926

Tomsk—1929

E. F. Chekhova

Counting the Number of Ions in the Atmosphere at the Meteorological Station of the Sib. Technological Institute in Tomsk in the Summer of 1926

Chapter I.

Literature Data.

Atmospheric electricity, in its various manifestations, aroused great interest already in times long past.

The beginning of scientific research was laid in the seventeenth century; in the following centuries the growth of electrometeorology as a science was observed, and at the end of the nineteenth century it took on an entirely new direction, thanks to the works of Elster and Geitel, who laid at the foundation of the doctrine of atmospheric electricity the ion theory, which is also accepted by modern science. According to this theory, as a result of ionization of the atmosphere ordinary ions are obtained (positive and negative), with a mobility of the order of \(1 \frac{\mathrm{cm}}{\mathrm{sec}} \frac{\mathrm{volt}}{\mathrm{cm}}\), and heavy ions (Langevin’s) with a mobility smaller by approximately 3000 times. The latter are formed as a result of the adsorption of some of the normal ions on solid and liquid particles and, in most cases, are negative¹.

According to the opinion of Prof. Tverskoi², in order to understand the essence of electrical processes in the atmosphere it is necessary to study not only ionization, but also the ionizers; “the most important ionizer is the radioactive substances contained in the atmosphere and the earth’s crust.”

According to theoretical calculations, the radioactive substances of the atmosphere cause the formation, in all, of \(2.85 \frac{\mathrm{ion}}{\mathrm{cm}^{3}\cdot \mathrm{sec}}\) (if the action of thorium and actinium is taken into account, there is an increase of 30–40%).

From observations, however, the number of newly formed ions has been found to be \(1.47 \frac{\mathrm{ion}}{\mathrm{cm}^{3}\cdot \mathrm{sec}}\) (in the case where, in calculations in the formula \(q = \alpha n^{2}\), \(\alpha\) is taken to have a value of the order of \(10^{-6}\), i.e., its usual value; but if \(\alpha\) is understood not as the recombination coefficient but as the coefficient of disappearance of ions, then the number \(q\) will be considerably larger.—Prof. Tverskoi’s indication).

According to the opinion of Prof. Tverskoi, the sources of radioactivity of the atmosphere are found predominantly in the earth’s crust; emanation, together with soil air, enters the atmosphere by diffusion “and as a result of the suction action of vertical and horizontal air currents.” The laws of this “breathing of the soil” are very complex.

It is known from observations that \(1\ \mathrm{cm}^{3}\) of soil air contains \(113000 \frac{\mathrm{ion}}{\mathrm{cm}^{3}}\). The influx of emanation and air from the soil depends on temperature, pressure, and is connected with the permeability of the soil.

Thus, radioactive substances play the principal role in a number of causes of atmospheric ionization—

1. The radioactive emanation itself, entering the atmosphere, ionizes its air, creating an equal number of ions of both signs;

2. Owing to the presence of radioactive substances in the soil, strong ionization of the soil air takes place; here, too, an equal number of positive and negative ions is created; the soil air rises through the earth’s capillaries, and the ions are adsorbed by their walls. “The coefficient of diffusion depends on the mobility of the ions; it is greater for negative ions; consequently, adsorption leads to a difference in the content of ions (of either sign¹).” “Predominantly negative ions diffuse to the walls of the earth’s capillaries; they are adsorbed by them, imparting a negative charge to the earth; the soil air, however, emerges with an excess of positive ions²).”

It is upon this latter fact that the “adsorption theory” of the emergence of the negative charge of the earth is built, as expressed by Elster and Geitel and supplemented by Ebert.

According to the conclusions of Elster and Geitel, the ionization of the atmosphere itself is small; according to the investigations of Thomson and Rutherford, the ionization on a summer day near the ground is 100,000 times weaker than in a roentgenized gas (even under the weakest X-rays)³); nevertheless, in greater or lesser quantity ions of both signs are always present in the atmosphere, and their number changes both periodically (over the course of the day and year) and nonperiodically under the influence of various factors that disturb and alter the normal course of phenomena.

As is evident from the literature, the elements of the atmospheric electric field have been investigated by many scientists; I shall dwell only on the results of observations concerning the values of the quantities \(n\), \(q\), \(E\)⁴). Below I shall give some results of these investigations.

The observational data show an undoubted dependence of the magnitude of the charge (in \(1\ \mathrm{m}^3\)) on geographical location.

Such a dependence, among others, is indicated by Mache and Schweidler in Western Europe⁵).

According to their calculations, on average the value \(E = 0.3—0.4\) ESE per \(1\ \mathrm{m}^3\), which gives about 1000 ions of both signs in \(1\ \mathrm{cm}^3\)⁶). Moreover, positive ions predominate.

Obolensky⁷) gives a table of the results of observations in Potsdam, Munich, Moscow, Säntis, and Karasjok.

From them, for \(E+\), the minimum mean value was in Moscow, \(+0.34\) ESE; the maximum mean value of it was observed in Munich, \(+0.53\) ESE; for \(E-\), the greatest mean value, \(-0.42\) ESE, was likewise in Munich; the smallest mean value, \(-0.13\) ESE, in Säntis.

¹) Obolensky. Geophysical Collection, vol. I, issue III, p. 57.
²) Ibid., p. 213.
³) Ebert, Phys. Zeitschr., 1901, 46, p. 664.
⁴) Notation: \(n\)—number of ions in \(1\ \mathrm{cm}^3\); \(q\)—ratio \(\frac{n+}{n-}\); \(E\)—charge in ESE in \(1\ \mathrm{cm}^3\).
⁵) Mache, Schweidler, “Die Atmosphär. Elektrizität,” p. 88, 1909.
⁶) Mache, Schweidler, Speransky, and many others, whose investigations and data relate to the period before 1911, took \(\varepsilon = 3.4 \cdot 10^{-10}\) ESE; if one takes it to be \(4.77 \cdot 10^{-10}\) ESE, the indicated number of ions changes by 29%; \(\varepsilon = 4.9 \cdot 10^{-10}\) gives a decrease of \(n\) by 31%.
⁷) Obolensky. Geophysical Collection, vol. I, issue III, p. 51 ff. Giving for \(\varepsilon\) the value \(4.7 \cdot 10^{-10}—4.9 \cdot 10^{-10}\) ESE, he gives the results of other investigators who took \(\varepsilon = 3.4 \cdot 10^{-10}\) ESE.

Positive ions predominate on average, especially on mountain summits; in the free atmosphere, however, with altitude the values of \(n+\) and \(n-\) become balanced.

Klossovsky¹, making a general summary of dispersion, also points to a predominance of \(n+\) over \(n-\), taking on average \(q = 1.18\). Kähler² gives, for the North German Lowland, a value of \(\bar E\) of \(0.2—0.4\) ESE in \(1\ \mathrm{m}^3\), for \(n+\) and \(n-\) \(400—800\) in \(1\ \mathrm{cm}^3\), for \(q = 1.1\); while indicating the predominance of \(n+\) over \(n-\), in general he notes a particularly large value of \(q\) over the ocean and explains this by Lenard’s effect with salt water (when a drop of salt water breaks up it becomes negatively charged, while the air becomes positively charged), and also by the adsorption of vapors predominantly on negative ions. In high mountains \(E+\) increases to \(1.1\) ESE (with \(\varepsilon = 4.9 \cdot 10^{-10}\) ESE)³. According to Kähler’s data, the number of ions over the ocean is smaller than over the continent. Witkiewicz⁴ holds the same opinion; he found that in Moscow and in the village of Kuchino the numbers \(n+\), \(n-\) are considerable, and \(q\) is close to 1 (for August \(q = 1.3\)). Mountain air, in his opinion, is strongly positively electrified. Large values are obtained for \(n+\) and \(n-\) in caves; according to his observations on 8/VIII 1924 in a cave:

Witkiewicz’s observations in Yalta over the course of several days in the summer of 1924 also gave, for the most part, a predominance of positive ions, as follows:

Of great interest are the results obtained by Speransky⁵ in Moscow; from four years of observations, the fluctuations of the mean monthly values (with \(\varepsilon = 3.4 \cdot 10^{-10}\) ESE) were

\[ \text{for } E+\,0.17—0.47\ \text{ESE},\quad \text{for } E-\,0.17—0.38\ \text{ESE}. \]

The maximum \(q\) in July is \(1.32\) (monthly mean), the minimum in November \(0.81\). In summer, on average, \(q\) increases from June to August.

The largest number of positive ions in Moscow was observed in summer, and of negative ions in autumn; the minimum was in winter.

By annual means, the number of ions in \(1\ \mathrm{cm}^3\) is \(940\) for \(n+\), \(880\) for \(n-\). In summer the mean number of positive ions is \(1210\). In summer positive ions predominate markedly, while in winter negative ions predominate slightly.

Absolute maximum in Moscow: \(3800\) per \(1\ \mathrm{cm}^3\) for \(n+\); \(3500\) per \(1\ \mathrm{cm}^3\) for \(n-\).

The absolute maximum \(q\) reaches \(8.7\).

According to Speransky’s data (p. 459 of the cited article), in the Observatory at Eskalemuir the results of observations are such that in part of them \(n-\) predominates. On examining the observational material of Speransky himself—

one can soon notice in some of them a predominance of negative ions, which is not present in the monthly means.

A very large number of observations has also been made on the course of \(E\), \(n\), \(q\). As an example I shall cite some of them. “The course is different in the same place at different times of the year and in different places at the same time”¹.

Mache indicates that Gockel found a maximum of \([E]\) after noon and at night (Freiburg); Schweidler obtained a maximum of \([E]\) in the morning (\(6^{\mathrm h}—8^{\mathrm h}\)) and in the first night hours, while by day there was a considerable minimum (Mattsee); Simpson (Karasjok), from three observations in a day, had a minimum of \(E+\) at \(6^{\mathrm h}—7^{\mathrm h}\) in the evening. W. Conrad (Säntis), from four days of observations, found the course less clear for \(E+\), and a clear minimum for \(E-\) after noon and a maximum at night.

According to the observations of Vitkevich², the maximum number of ions of either sign occurs in Yalta at \(1^{\mathrm h}\) in the afternoon. Obolenskii³ believes that “in general the diurnal course has not been established, especially since there are almost no night observations.”

Thus, in Speranskii’s rich materials⁴ over several years for Moscow there are only 3–4 days with observations over a full twenty-four hours. He devotes his chief attention to the annual course.

The annual course of the values \(E+\), \(E-\), as, in general, for middle latitudes, is simple, with a maximum in August and a minimum in winter, in January. Simpson obtained the same simple course in Lapland, but with the maximum in spring. Of course, the normal course for a given place may be outlined, but, owing to various causes, partial and sometimes considerable deviations are possible.

I shall cite some data from the literature on the question of the influence of meteorological and other factors on \(E\), \(n\), \(q\) and their course. Keller⁵ points to a decrease of \([E]\) with an increase in pressure, with an increase in relative humidity, in fog, haze, etc., and notes a direct dependence on temperature. At the same time, he speaks of the presence of dust as a cause of replenishing the air with negative ions, referring to observations in Batavia (and sometimes also in Central Europe), when for this reason the air appeared negatively charged relative to the earth; \(q\) is greatest in fog and haze; clouds, in his opinion, act analogously to dense fog. Smoke has the sign \(+\) or \(-\); it exerts an influence on the field at distances greater than 300–400 m.

Mache and Schweidler⁶ give the results of observations by Simpson and Gockel, who obtained a parallelism between the course of the number of ions and temperature. From other data cited by them it is evident that an increase in relative humidity lowered \(E-\) and \(E+\), which was especially reflected in \(E-\); a deep fall of pressure corresponded to larger values of \([E]\); results contradicting the latter conclusion were obtained by Gockel and Schweidler; from independent studies they found that, when the barometer was steady, \(E\) was higher than when it was falling. All investigators agree that any turbidity of the atmosphere lowers \(E\). Keller notes, during the fall of precipitation and afterward, an increase in the number of negative ions⁷. According to

according to his indications, before storms and thunderstorms \(q\) reaches an exceptional value.

Researchers differ as to the influence and sign of the charge of clouds.

Prof. Tverskoi¹ indicates that, according to Wigand’s experiments, “in radiation (anticyclonic) fogs” positive charges of droplets predominate; “in mixing fogs” no such exceptional predominance is observed, and, moreover, in radiation fogs the charges of the fog droplets are higher.

For Russia, the results of Speranskii² are of interest, concerning the dependence of the course of \(n\), \(E\), \(q\) on meteorological elements. From his summer observations it is evident that the influence of changes in pressure is insignificant and is manifested chiefly in positive ions. A decrease in the number of ions with increasing pressure was observed for negative ions from 732 mm, and for positive ions from 742 mm; at lower pressures no such dependence was established.

Speranskii ascribes the principal importance to changes in temperature. With an increase in temperature up to \(17.6^\circ\text{C}\), an increase in \(n+\) and \(n-\) is observed; thereafter there is already a decrease, since the soil dries out and dust rises, reducing the transparency of the atmosphere. The maximum of \(E-\) is at \(15^\circ\), and of \(E+\) at higher temperatures.

With an increase in absolute humidity, \(E\) increases and, together with it, \(q\); but an increase in absolute humidity above 13–15 mm leads to a decrease in \(E\) (especially \(E-\)). \(E+\) reaches a maximum at temperatures above \(25^\circ\text{C}\), under the indispensable condition, however, that the absolute humidity not exceed 13–15 mm. High relative humidity lowers \(E\) (especially \(E-\)). Speranskii found no definite dependence of \(n\) on precipitation. He did not establish the dependence of the charge on the degree of solar radiation, owing to the unfavorable urban conditions of the observations. In the literature, the question of the action of solar rays is treated in divergent ways³,⁴.

Solar rays, on the one hand, contribute to a rise in temperature and, consequently, to the formation of ascending air currents that carry ions upward; on the other hand, through their ultraviolet component they exert a photoelectric action. The shorter (energetic) ultraviolet Schumann rays \((\lambda = 90\text{–}180\ \mu\mu)\) are absorbed by the higher layers of the atmosphere. The rays that reach the earth are considerably weaker; they are incapable of ionizing the air and act only on its impurities (apart from water droplets), acting on them photoelectrically.

Falling on the surface of soil containing granite, limestone, and feldspar, even weak ultraviolet rays cause the emission of electrons.

As can be seen from the few literature references cited above, since 1899 many interesting and important questions in the field of electrometeorology have been investigated.

The data cited indicate that the results of investigations on individual questions (for example, the course of \(E\) and its limiting values) are extremely contradictory.

An attempt to carry out observations—admittedly not long in duration—was made by me in the summer of 1926 at the meteorological

station of the STI in Tomsk. The purpose of the work, to which I shall now turn, was—

1. To determine the values \(n+\), \(n-\) \((E+, E-)\), \(q\);
2. To outline, insofar as possible, the normal course of these quantities, and also to clarify their connection with various factors and meteorological elements.

Chapter II.

Apparatus and conditions of observation.

The work of counting atmospheric ions by means of an aspiration apparatus—the “Ebert ion counter”—was carried out at the meteorological station of the STI in the city of Tomsk during the summer period of 1926 (chiefly in June and July; separate observations were also made in August and September).

The use of Ebert’s counter is based on the fact that the magnitude of the fall of the leaves of a charged electroscope, corresponding to \(1\ \mathrm{m}^3\) of air drawn by a ventilator through the condenser of the counter, can serve as a measure of the ionization of the atmosphere.

The Ebert apparatus belonged to the physical laboratory of the STI. Before the beginning of the investigations, the capacitance of the counter condenser was determined and calculated, and the scale of the electroscope was graduated (the capacitance of the condenser was found to be \(22.9\ \mathrm{cm}\)). This preliminary work was done by me with the assistance of lecturer of T. G. U. M. P. Orlova in the laboratory of inorganic chemistry of T. G. U.

As a result of the graduation I constructed a curve of the dependence of the sum of the deflections of the electroscope leaves (from the middle of the scale) on the potential to which the latter is charged.

Separate series of observations were carried out at three points—

Point I—the meteorological booth; it is located almost in the center of a large yard (about \(10000\ \mathrm{m}^2\)), partly paved with cobblestone and partly packed with slag, surrounded on three sides by three-story stone buildings of the institute; only on its fourth side are there low wooden structures. The two nearest buildings are whitewashed. The distance from the booth to the nearest of the multi-story buildings is not less than \(30\ \mathrm{m}\), so that its shadow, like the shadow of the poplar avenue running west of the enclosure of the meteorological station, did not fall on the place where the apparatus was installed. The counter was located on the stairs of the meteorological booth at approximately a height of one meter above the ground (covered with grass).

The grounding of the electroscope casing was accomplished by means of a wire soldered to a meter-long metal rod driven almost completely into the ground (the soil was clayey and compact).

Point II—the front garden, situated on the southern side of the physics building and separated from the street by a lattice fence. The basement windows open into it and are usually closed. The trees in the front garden are sparse; the soil is clayey and covered with herbaceous vegetation.

Grounding was carried out by attaching a wire from the casing to a water pipe leading out into the garden. The apparatus was installed near the wall of the building, close to a row of poplars, in their shade, at a height of approximately one meter above the ground.

Point III—the upper open platform on the tower of the institute’s physics building, located \(20\) meters above the ground¹. Here

several separate observations were made that were not of a systematic character. A gas pipe extending to the tower served for grounding.

As is evident from the above, there were no special devices for installing and protecting the instrument, which made it impossible to work in wind and precipitation; therefore the material collected by me pertains mainly to calm and rainless weather. Most of the observations were carried out at point I.

The Technological Institute is located within the city, close to an electric power station, a factory, and coal depots, which accounts for the almost constant presence of coal dust in the air.

The three-story buildings of the Technological Institute disturb the uniformity of the atmospheric electric field at the observation site, since, bending according to the shape of the buildings, the equipotential surfaces around them are closer together than over a horizontal and level surface.

Since the elements of the electric field can be spoken of only with reference to a given place and at a definite time, regularity in time and unity of place were observed as far as possible. On the selected days observations were made from 8–9 h in the morning until approximately 9½ in the evening, at intervals of 2–3 hours; meteorological observations were conducted in parallel. There were no night observations. In determining the number of ions in 1 cm³, observations of ions of each sign were carried out for approximately 20–25 minutes (counting from the moment the ventilator was started): 10 minutes with the ventilator operating, and 10 minutes without it, with the upper tube closed, in order to determine the loss of charge due to imperfect insulation.

The electroscope was charged to approximately 200 v (as in Ebert’s own experiments). The calculation of \(E\) in electrostatic units was made by the formula

\[ E=\frac{C\Delta V}{300\cdot M}, \]

where \(C\) is the capacitance of the condenser, calculated by me and equal to 22.9 cm. \(\Delta V\) is the fall of potential through dispersion (caused by air ions). \(M\) is the mass of air drawn through by the ventilator in m³, recorded by the counter at the ventilator; \(E=n\varepsilon 10^6\), where \(n\) is the number of ions in 1 cm³, \(E\) is the charge of 1 m³ (in ESE), \(\varepsilon\) is the charge of the electron (equal to \(4.77\cdot 10^{-10}\) ESE); \(q\) was calculated by the formula

\[ q=\frac{n+}{n-}. \]

The Ebert apparatus captures almost completely only normal ions; ions of low mobility, however, are captured by it only in part¹. Thus, an increase in the number of heavy ions (for whatever reasons) already gives a decrease in the total number of ions counted by this counter.

As a consequence of the above-mentioned unipolarity of the heavy ions, the free charge in 1 m³, \(\delta\), equal to \((E+ - E-)\) ESE, could not be determined by Ebert’s method².

Chapter III.

Results of Observations in Tomsk.

To establish the laws of variation of any quantity, a large number of observations and a considerable interval of time are necessary. The number of days with systematic observations at my disposal is limited, and therefore one can speak only of the emerging normal course of the elements \((n, E \text{ and } q)\) and try to clarify the causes that produced deviations from it, depending on meteorological and other factors.

All the results of the observations are given in Table I, with a brief characterization of the individual days; for greater clarity, curves of the course of the individual elements \((n+, n-, q)\) are appended to the work, Table III.

As is seen from them, for the values of the quantities \(n+\) and \(n-\) there appeared a double daily course, where

I minimum in the morning (probably after sunrise),
I maximum before noon (about \(11^{\mathrm h}\) a. m),
II minimum after noon (for \(n+\), usually at \(1^{\mathrm h}\)—\(3^{\mathrm h}\) p. m; for \(n-\) for the most part about \(5^{\mathrm h}\)—\(6^{\mathrm h}\) p. m),
II maximum, probably at night.

An increase toward evening for \(n+\) and \(n-\) is noted on the majority of days with a normal, undistorted course.

It is extremely difficult to take account of the daily course of \(q\), since in it the variation of the values of \(n+\) and \(n-\) is combined. The maximum at \(5^{\mathrm h}\)—\(7^{\mathrm h}\) p. m. possesses great constancy in the daily course of \(q\) (on normal days). Often soon after noon a minimum of \(q\) is observed, but it does not have a constant character. Summing up the results obtained by me, one may point to the great similarity in the course of the values of \(n+\), \(q\) in Tomsk and Vienna, only the morning I maximum for \(n+\) in Vienna is at \(9^{\mathrm h}\) a. m. (in Tomsk at \(11^{\mathrm h}\) am), and the minimum of \(q\) in Vienna at \(10^{\mathrm h}\) am (for Tomsk, more often after noon).

The course of \(n-\) for Tomsk is similar to that of Potsdam¹.

Table II is a summary of the observations on the elements \(q\), \(n+\), \(n-\), \(E+\), and \(E-\) (observations on the tower are not included).

Table II.

I column. Mean values for the whole period for the elements under investigation \((q, n+, n-, E+, E-)\) (all observations were taken into account).

II column. Means from observations; in the months of June and July a larger number of observations was made. But these data are not—

are monthly means, since the observations were not daily. These two columns (I and II) were compiled from observations of all days with any number of observations per day. No division of days into clear and cloudy was made, in order to avoid arbitrariness of selection.

Column III. “Maximum (minimum) of mean daily values.”
All mean values were computed for days with not fewer than 3 observations; from the daily means the maximum and minimum were taken.

From the results of my observations presented above, it is seen that the number of ions in \(1\ \mathrm{cm}^3\) does not remain constant; it varies from day to day.

The mean number of ions per day fluctuates for \(n+\) from 100 to 279, and for \(n-\) from 136 to 302.

In general, there is noticed, as it were, some increase in the number of ions, according to mean daily observations, from June to July.
The minimum daily mean for \(n+\), \(n-\), \(E+\), \(E-\) falls on 23/VI
The maximum ” ” ” ” ” on 7/VII

The mean value for the whole period for \(E+\) is 0.08 ESE per \(1\ \mathrm{m}^3\)
” ” ” ” ” \(E-\) 0.10 ESE per \(1\ \mathrm{m}^3\)
” ” ” ” ” \(q\) close to unity (0.9)

Maximum daily mean over the period for \(q\): 1.6, 26/VIII
Minimum ” ” ” ” ” 0.57, 16/VI

An abnormality in the daily course may be noted—

for \(n-\), 26/VIII,
for \(n-\) and \(n+\), 30/VI.

1) 26/VIII (observations in the booth)
Mean for the day: \(n+ = 205,\ n- = 151,\ q = 1.5\)

The course of \(n-\) is completely anomalous; the fall of the value of \(n-\) toward evening was also reflected in the course of \(q\), causing a rapid rise of the latter from 3 h p.m.

The course of \(n+\) is normal, but its extreme values are very sharp.

2) 30/VI (observations in the booth)
Mean for the day: \(n+ = 142,\ n- = 208,\ q = 0.66\)

Anomalies:

1. for \(n-\), a fall from the earlier morning hours to 11 h a.m.,
2. absence, after noon, of a minimum of \(n-\), \(n+\).

Minor deviations from the established course, not, however, disturbing its normal character, occurred on 16/VI, 19/VI, 7/VII, 9/VII, 6/IX.

I. 16/VI (in the booth)
Mean values: \(n+ = 125,\ n- = 235,\ q = 0.57\)

There was observed: 1. a shift of the minimum of \(n-\) to 3 h p.m.,
2. a fall of \(n+\) toward evening

II. 19/VI (in the booth)
Mean values: \(n+ = 163,\ n- = 231,\ q = 0.76\);

It was noted: 1. a shift of the first maximum of \(n+\) and \(n-\) to 4 h p.m.,
2. a shift of the minimum of \(n+\) to 5 h p.m.

III. 7/VII (in the palisade)
A delay of the minimum of \(n+\) was observed (by 2–3 hours).

IV. 9/VII (in the palisade)
Mean for the day: \(n+ = 173,\ n- = 232,\ q = 1.13\)

There occurred: 1. a fall of \(n-\) from morning to 11 h a.m.,
2. a shift of the afternoon minimum for \(n-\) to 2 h of the day,
3. a shift of the maximum of \(q\) to 2 h p.m.

V. 6/IX (in the booth)

Mean value \(n+ = 168,\ n- = 231,\ q = 0.92\);

Noted:
1. a shift of the morning maximum of \(n+\) to the afternoon hours,
2. a fall of \(n-\) from morning to \(11^{h}\) am,
3. a shift of the maximum of \(q\) to \(2^{h}\) pm.

The daily course of the values \(E, n, q\) depends on the course of changes in the amount of emanation near the soil, the release of ionized air from the ground, and changes in the transparency of the atmosphere.

Guided by the indications of Prof. Tverskoi¹) concerning changes in the amount of emanation at the soil and by Obolenskii’s description of the terrestrial electric field,²) and also taking into account certain considerations of our own, it is possible, in general, to give a brief explanation of the daily course of the values \(n+\) and \(n-\) observed in Tomsk in the summer of 1926. The maximum amount of emanation at the earth’s surface falls at 2–3 o’clock at night (minimum at 16–17),³) the air is transparent, since adsorption nuclei are almost absent, and the number of light ions is large. The nocturnal cooling of the earth’s surface reaches its maximum toward sunrise; the elasticity of the air in the upper layers of the soil decreases; a current of air appears from the atmosphere toward the earth, which will hinder the escape of emanation and soil air until the soil has warmed sufficiently. As a consequence of the above-mentioned phenomenon, and also owing to the decrease in the transparency of the atmospheric air from the fog that rises after sunrise, there appears a morning minimum in the number of ions.

As the earth is heated by the sun the atmosphere becomes more transparent, i.e., ascending currents appear, though still weak, carrying away the fog; the soil gradually warms, and the number of ions near the earth again increases, but the currents are still weak and carry upward only an insignificant number of ions; consequently, around \(11^{h}\) am one may expect a maximum of \(n+\) and \(n-\). By noon and later the ascending currents gradually become stronger and become capable of carrying upward from the earth air rich in emanation and, in general, in ions; gradually this process gains the upper hand over the influx of soil air and emanation from the earth. The transparency of the atmosphere decreases after noon; a large admixture of dust appears in the air, since the surface layer of the soil dries out under the action of the sun’s rays. All the processes mentioned above produce a lowering of the number of ions, and in the afternoon period it reaches its minimum; but the matter is complicated by the following circumstances:

1. The presence of adsorption nuclei contributes chiefly to a decrease in \(n-\), since negative ions are adsorbed more rapidly than positive ones, as having greater mobility;⁴) consequently, the number of readily mobile negative ions decreases to a greater extent than that of \(+\) ions.

2*. On the other hand, under the action of solar rays of short wavelength, dust particles may emit electrons, as was already indicated above.

The maximum strength of the ascending air currents usually occurs 2–3 hours after noon; ions are carried upward from the earth, and the number of ions after \(11^{h}\) am falls. If attention is paid to the course of \(n+\) and \(n-\) separately after noon, then the minimum of \(n+\) falls in the period of strong ascending currents (\(1^{h}\)—\(3^{h}\) pm). The maximum of the photoelectric effect

¹) Tverskoi. Journal of Geophysics and Meteorology, III, vol. 3–4, pp. 196–207.
²) Obolenskii. Geophysical Collection, vol. I, issue 3, 1914, p. 29.
³) Tverskoi. Journal of Geophysics and Meteorology, III, vol. 3–4, p. 202.
⁴) Obolenskii, Geophysical Collection, vol. I, issue 3, p. 57.

Kähler¹ assigns the action of the sun’s rays to the period from \(11^{\mathrm h}\) to \(1^{\mathrm h}\) p.m.; perhaps his results also apply after noon. One may suppose (though, to be sure, with great caution) that the minimum of \(n-\) perhaps lags behind \(n+\), namely, as a consequence of phenomenon “2” (indicated above), and occurs only when the sun’s rays have already weakened (toward \(5^{\mathrm h}\) p.m.) and the dust in the air only diminishes its transparency, while condensation of vapors on dust particles and currents toward the earth are still weak. From \(5^{\mathrm h}\) to \(6^{\mathrm h}\) p.m. the temperature falls more sharply, the ascending currents that carry ions away already weaken; descending currents, directed toward the earth and carrying ions to the lower layers of the atmosphere, gradually gain the upper hand. Moreover, owing to the fall in temperature, condensation of vapors occurs, chiefly on dust particles; the air is purified, and the atmosphere is enriched with readily mobile ions of both signs. The number of ions thus increases toward evening.

The maximum of \(q\) (\(5\)–\(7^{\mathrm h}\) p.m.) coincides in time with the moment of the minimum of \(n-\) and of the increase already of \(n+\), owing to the occurrence of descending currents; later \(n-\) also increases, and therefore the value of \(q\) falls toward evening. The minimum of \(q\) falls in the period of stronger ascending currents; this indicates a more rapid decrease under them of \(n+\) than of \(n-\). But, as indicated above, this minimum does not have a constant character.

Having examined the results of my observations in Tomsk that pertain to the normal course of the elements \((E, n, q)\), I shall turn next to the influence upon them—noticeable, at least in part, in Tomsk—of meteorological elements and factors. It is very difficult to speak of the absolute influence of any one meteorological element separately (for example, temperature, atmospheric pressure, absolute and relative humidity, precipitation, solar radiation, etc.), since they are always combined, and the weather is always only an inseparable complex of them.

For completeness of the survey it is also necessary to consider the influence of dust, smoke, low clouds, and other accidental factors that disturb the normal course of change in the number of ions². The insufficiency of the observations does not make it possible to draw any decisive conclusions, but, in general, the relationships between the number of ions and meteorological factors that have been established for other points on the earth’s surface are confirmed.

Dependence of the course of \([n]\) on meteorological elements and various factors.

In Tomsk, parallelism in the course of \([n]\) and temperature was observed only in the morning hours (from \(8^{\mathrm h}\) to \(11\)–\(12^{\mathrm h}\) a.m.); thereafter this parallelism was not observed. The picture becomes obscured after noon by the action of the sun’s rays (ascending currents, possible influence of the photoelectric effect, etc.). Toward evening the fall in temperature is already accompanied by an increase of \([n]\), since the lowering of temperature favors a convective current (directed toward the earth) and a decrease in the number of adsorption nuclei (a detailed discussion of all that has been said is in the preceding chapters).

The dependence of \([n]\) and \(H\) (atmospheric pressure) is inverse, observed chiefly in the second half of the day. It is especially difficult to distinguish the influence of these two elements—pressure and temperature.

No dependence of \([n]\) on \(t\), \(H\), or \([n]\) in passing from one day to another was observed, owing to the comparatively limited number of days of observations. For humidity the dependence is still less constant; often, in the daily course, the maximum of absolute humidity and of large values of \(n+\) in the evening are close in time; sometimes there is a coincidence of the minima of these quantities. Individual cases were observed of partial parallelism in the course of absolute humidity and \(n-\). It is still more difficult to speak of relative humidity; in general, an inverse course with \([n]\) was noticed somewhat more often.

Low clouds exerted an obvious influence, perhaps partly by their charges, but chiefly as obstacles to the air currents rising during the daytime and carrying ions upward; by holding the ions near the ground, low clouds increased the values of \([n]\); if the clouds dispersed, then \([n]\) fell.

Thus, on 30/VI the absence after noon of a minimum for \(n+\) and \(n-\) can be explained precisely by the presence of low clouds (taking into account the high temperature and the cyclonic type of weather, which promoted the emergence of ionized soil air and emanation).

On 6/IX the lower cloudiness, during the hours of ascending currents, produced an accumulation of positive ions, which explains the displacement of the maximum of \(n+\) from 11 a.m. to 2 p.m. (normally from 11 a.m. to 2 p.m. there should be a decrease). The wind that rose after 2 p.m. dispersed the clouds; the value of \(n+\) immediately fell, and the decrease continued until evening. The maximum of \(q\) shifted on this day to 2–3 p.m.

No dependence of the number of ions on the direction of the wind was noticed. Wind reduced the transparency of the air, raising dust and particles of coal in dry weather. With a strong wind it was impossible to make observations, since there was no suitable protection.

The presence of dust lowered, on average for the day, the amount of \(n-\) and \(n+\) (although for \(n-\) during the day there was an increase in the presence of dust, perhaps as a consequence of the photoelectric action of the sun’s rays, and also, possibly, because with a considerable content of dust it, being negatively charged, removed part of the positive charge of the electroscope).

The presence of smoke also reduced the mean daily value of \(n-\) and \(n+\); although in the daytime an increase in the number of ions was sometimes produced under the influence of haze (smoke from forest fires), it, like low clouds, held back the ascending currents. Smoke in the morning hours produced a delay in the points of the course.

Thus, on 19/VI, in the presence of smoke and dust, all extreme values were delayed by about 2 hours; the character of the course of \(n+\), \(n-\) during the day remained normal.

The delay of the 1st maximum of \(n+\) and \(n-\) (by 2 hours) is quite explicable from the point of view of an accidental accumulation of ions, owing to dense haze (even with weak ascending currents). The rise of the curve of \(n+\), \(n-\) continued until the moment when the smoke weakened (approximately until 1 p.m.).

It is interesting to note that the minimum of the mean values of \(n+\), \(n-\) for the day falls on 23/VI—a day with air of low transparency, dust, and smoke from forest fires.

The day of the maximum of the mean daily values of \(n+\), \(n-\), 7/VII, is distinguished by clean transparent air. The influence of fog in Tomsk was not investigated because there were no foggy days during the period of observations. From individual observations it was noticed that a short rain that had passed mostly increased the value of \([n]\) (though there were individual exceptions); some partial deviations in the daily course may perhaps be partly explained by the influence of rain.

Thus on 30/VI the minimum of \(n-\) at \(5^{h}\) p.m. was evidently due to rain. On 9/VII, after rain during the preceding night, there was an anomalous fall of \(n-\) from morning to \(11^{h}\) a.m.

The explanation for the increase of \(n-\) after rain may be sought in the following:

1. rain cleanses the air, makes it more transparent, destroys dust, and thereby increases the number of light ions.
2. The Lenard effect¹ partly also takes place (although the latter acts very weakly).

As to the influence of a thunderstorm, no conclusion can be drawn from our Tomsk observations, since the observation was carried out only once, at the beginning of a thunderstorm, and only for \(n+\). Further observations were interrupted by a hurricane. For \(n+\), small values were obtained.

Measurements after a thunderstorm, hail, and a downpour gave an average number of ions and weak unipolarity; observations in Potsdam during a hurricane and thunderstorm gave analogous results².

The explanation of partial anomalies in the course (and deviations) in the summer of 1926, as is clear from the examples given above, must be sought precisely in the influence of some of the factors indicated here (fog, low clouds, dust, rain, etc.)³.

The deviations in the course of \(n-\), \(n+\) observed on 9/VII must be considered quite separately, as depending on purely accidental causes; the shift of the afternoon minimum for \(n-\), \(n+\) requires a detailed explanation:

The observations on 9/VII were made in the garden near a window into the basement, which was opened after noon. The normal fall of the values \(n-\), \(n+\) from \(11^{h}\) a.m. toward noon (and further) was interrupted at \(1^{h}\) p.m., and an increase in the values of these quantities began.

The explanation must be sought in the opening of the window into the basement after noon. The air became enriched with ions of both signs, possibly owing to the ionized air of the basement and to emanation.

The number of ions on that day was considerable; positive ions predominated in the second part of the day (which is quite natural if one assumes the influence of basement air). True, the clear weather and the transparency of the air also contributed to significant ionization of the atmosphere on that day.

The maximum of \(q\) was evidently assigned to the time shortly after the opening of the window into the basement.

The positive unipolarity of the air gradually decreased toward evening.

From all the data presented it is clear that the following are peculiarities of the results of our Tomsk observations:

1. A comparatively small number of ions in \(1\ \mathrm{cm}^{3}\) (although the order of \(E\) here coincides with the order of this quantity in other places), and
2. The predominance, in the majority of cases, of \(n-\) over \(n+\). The causes of these peculiarities must, of course, be sought in the position of the observation site and in the character of the weather in the summer of 1926.

The small number of ions may be a consequence of insufficient transparency of the atmosphere, generally in the city (especially during drought), and

of the low permeability of the soil at the observation site. The latter partly explains also the second peculiarity—the predominance of \(n-\) over \(n+\). It is possible that the predominance of negative ions in the observations in the summer of 1926 in Tomsk at the meteorological station of the STI is explained in part by the photoelectric action of the sun on particles of dust and coal, almost constantly present in the air near the place of observation (the latter supposition is, in part, as if confirmed by the fact that in observations in the front garden, where there are no coal particles, there was 55% negative unipolarity, whereas in the investigations at the station booth in the courtyard there was 63%).

In Keller’s opinion, “the photoelectric action of the sun’s rays may quite well be invoked to explain the predominance of \(n-\) at the earth’s surface at midday”¹.

Perhaps a distorting influence is exerted by the cobblestone pavement² with which the courtyard is paved, the limestone facing of the buildings, and in part their stone granite foundation; the action of the sun’s rays on granite and limestone spar \((\mathrm{CaCO}_3)\), etc., was indicated above. But nevertheless one cannot base oneself entirely on the photoelectric action of the sun’s rays in explaining the predominance of \(n-\) in our observations; perhaps the action of the dust particles themselves also partly takes place, which are raised by the wind from the ground and, being negatively charged, can somewhat discharge a positively charged electroscope.

The result indicating the predominance of negative ions perhaps needs confirmation.

Resumè

The experiment of counting ions with the aid of Ebert’s aspiration apparatus, carried out by me in the summer of 1926 at the meteorological station of the STI in the city of Tomsk, showed that the atmospheric air was comparatively little ionized.

On average: \(n+ = 190\), \(n- = 231\), \(q \doteq 1\), with \(\varepsilon = 4.77 \cdot 10^{-10}\) ESE.

Consequently, \(n-\) prevailed over \(n+\); the reason for this must be sought chiefly, probably, in the local conditions and in the peculiarities of the weather of the summer of 1926.

As a result of the work, a certain normal course was outlined:

For \(n+\), with an increase toward 11 h a.m. and toward evening, with a minimum at 2 h–3 h p.m.;

For \(n-\), likewise with an increase toward 11 h a.m. and toward evening, with a minimum at 5 h–6 h p.m.

The maximum of \(q\) was observed, for the most part, at 5 h–6 h p.m.

A deviation of the course of \([n]\) from the normal was noted, chiefly under the influence of low clouds, fog, dust, and partly from non-prolonged rain. The dependence of \([n]\) on thunderstorms and wind direction was not investigated.

There were no observations either during strong wind or during widespread rains, owing to the absence of protection.

In concluding the work I consider it my duty to thank Prof. I. A. Sokolov for the opportunity provided to carry out observations at the meteorological station of the STI, and also for advice, guidance, and editorial changes to the work; Prof. P. N. Tverskoi for reviewing the work and for valuable suggestions; and instructor M. P. Orlov for participation in the preparatory part of the investigations.

Table 1. Observations at the meteorological station of STI

Table II

Meteorological shelter of the station (yard)

Back room

Dates shown: 16-VI, 19-VI, 23-VI, 30-VI, 26-VIII, 6-IX, 7-VII, 9-VII.

Side headings: place of observation; atm.; \(t^\circ, q\).

Legend:

\[ -\!\cdot\!-\!\cdot\!- \quad q=\frac{n^+}{n^-} \]

\[ -\,-\,- \quad n^- \]

\[ \_\_\_ \quad n^+ \]

The plotted quantities are \(q\), \(n^-\), and \(n^+\), with scales marked from \(0\) to \(600\) for ion counts and from \(0\) to \(3.0\) for \(q\).

1. Keller, Atmospheric Electricity, 1923. ↩↩↩↩↩↩↩↩↩↩

2. “Cobblestone”—fragments of rock, chiefly granite and limestone rocks. ↩↩↩↩↩↩↩↩

3. I leave some anomalies without explanation, since I find it difficult to indicate their causes. ↩↩↩↩

4. Köhler, “Atmosph. elektr-vo,” 1923. ↩↩↩

5. Keller, “Atmospheric Electricity,” 1924, pp. 80, 35, 30, 71. ↩↩

6. Mache, Schweidler. “Die Atmosphär. Elektrizit.” 1909, pp. 90–92. ↩

7. Keller, “Atmosph. Electr.” 1923, pp. 42, 72, 71. ↩