IONS IN THE ATMOSPHERE 
The small-ion content of the lower atmosphere is 
generally lowest during the winter months and highest 
during the summer, just opposite to that found for the 
large-ion content. The values usually reach a maximum 
during the morning hours and a minimum during the 
afternoon. This type of variation, while largely con- 
trolled by the variation in large-ion content of the air, 
also depends to some extent upon the variations in the 
rate at which ions are produced, which, according to the 
curves of Fig. 1, is greatest durimg the early morning 
hours. 
Variation in Ion Concentration of the Atmosphere with 
Height above Ground 
The value of the large-ion concentration of the atmos- 
phere at various heights above the ground can only be 
inferred from the values of condensation nuclei obtained 
at various altitudes. Wigand [20] made fourteen balloon 
flights on which condensation nuclei were measured. 
A rapid decrease in concentration with altitude was 
found; at a height of 3 km the concentration was only 
3 per cent of that at ground level. 
125 
Much more information is available concerning the 
value of the ratio m/n2, how it varies and why, than 
there is concerning the ratio Ni/N». Moussiegt [25], 
from observations in the Alps, found mean values of 
2214 and 2335, respectively, for N, and No, from which 
one would deduce a value of 0.95 as the ratio of N,/No. 
Hogg [15], in Canberra, Australia, found a mean value 
for this ratio of 1.22. In Washington, D. C., continuous 
records (unpublished results) of large, small, and inter- 
mediate ion concentration of air, alternating each week 
between the positive and negative ions, were made 
during September and December, 1935. Since these 
data are not strictly simultaneous, the ratios can be 
regarded as only approximate. In view of the paucity of 
published data from which a comparison of positive- 
and negative-ion content can be made, a summary of 
these data seems worth while and is given in Table 
IV. The large-ion concentrations in ions per 10-2 cc are 
represented by N, and No, while My, Ms, and m, nz 
represent the positive and negative intermediate-ion 
and the positive and negative small-ion concentrations, 
respectively, mm ions per cc. The ratios M,/M, and n/n2 
Tape [V. Means or Various Hourty VALUES OF VARIOUS HLEMENTS IN WASHINGTON 
Elements 
Means of Month (1935) 
M No MM Mo ny n2 Ni/N2 Mi/Me2 m/n2 
5 largest........... er 72.4 121 126 284 266 1.49 1.05 1.19 
osmallest.......... 35.8 27.3 94. 91 180 145 1.00 0.95 1.01 September 
All values......... 51.1 42.8 107 108 229 212 1.10 1.00 1.10 
mplancest....0...... 19).3 74.0 167 195 169 159 27 1.01 1.22 
Ssmallest.......... 46.8 38.5 139 139 128 108 0.98 0.90 1.01 December 
NIL S92) (a 60.8 48.8 153 170 188 173 112 0.96 Wow?) 
The values of the small-ion concentration made on 
thirteen balloon flights by various observers and that 
deduced from Haplorer II air-conductivity measure- 
ments have been summarized by Gish [6, p. 194]. He 
concludes that the concentration increases roughly by 
1000 ions per ce (one sign) for each 2-km increase in 
altitude. This rate of increase is true up to an altitude 
of about 6 km, after which it gradually diminishes, 
according to the Hxplorer II data, to less than half 
this value at 14-km altitude. 
Ratio of Positive-Ion to Negative-Ion Concentration 
A relationship between the ratios N,/N» and n/n» has 
been deduced by Gish [6, p. 183] from the equilibrium 
equations and is given by the equation 
(m/n2)? = bNi/aNo, 
Where a = m0/n and b = 720/n». If one assumes that 
mo0/720 = m»2/nx, then from the equation above it 
follows that 
(1/2)? = (20/10)? Ni/Ne, 
Which is the relationship assumed by Nolan and de 
Fachy [26] 
show no consistent diurnal variation, while the ratio 
N,/N2 varies more or less in a manner opposite to that 
of the large-ion content [49]. 
During fair weather the average concentration of 
positive small ions exceeds that of the negative small 
ions by 10 or 20 per cent. Particularly at certain sta- 
tions, the ratio m/n. varies in a manner similar to the 
variation of the earth’s field (electrode effect). This is 
due to the repulsion of negative ions by the negatively 
charged ground. During a thunderstorm, because of the 
intense electric field with frequent changes in sign, the 
ratio undergoes frequent changes in value, say from a 
very high to a very low value and vice versa, usually 
several times during a storm. 
Mean Life of an Ion 
The mean life of an ion is the time interval between 
formation and destruction of the average ion. For small 
ions the mean life 7, in seconds, for the case when large- 
ion concentration is sufficiently small, is given by the 
equation 
™ = n/q, (8) 
in which n represents the small-ion concentration and 
q, the rate of ionization (rate of small-ion formation). 
