IONS IN THE ATMOSPHERE 
Now the balance of large ions, shown later, requires 
that 
moN 1 = m2N ne, (3) 
and similarly for the negative ions: 
moN ones = meNonr. (4) 
If one further assumes that (3) is equal to (4), then 
(2) can be rewritten as 
g = 2m2nNo, (5) 
so that, if changes in q are neglected, the value of m 
is approximately inversely proportional to N». 
Processes which cause the destruction of small ions 
other than those involving combination with small or 
large ions or condensation nuclei can play an important 
part under some conditions. Large particles such as 
smoke and dust can remove small ions [2, 48]. In the 
atmosphere over the oceans the most important process 
of destruction of small ions is recombination, but 
here the influence of nuclei is perceptible in the balance 
of small ions [44]. In this connection it is interesting to 
mention the results of a long series of observations of 
atmospheric conductivity over the oceans. A steady 
decrease has been noted since 1912, indicating that even 
here there is a gradual accumulation of atmospheric 
pollution, due apparently to the increasing industrializa- 
tion over the world [48]. 
Recombination of Small Ions 
This subject has been extensively studied, both theo- 
retically and experimentally. The reader is referred to 
the exhaustive treatment given by Loeb [22], and by 
Jaffé [18]. The subject cannot be pursued here; however, 
a word about columnar recombination is in order. In the 
high ion-density track or column left by an alpha parti- 
cle there will be a high rate of columnar recombination. 
Thus the effective rate of ion formation is less than 
that which actually occurs. Only those ions which escape 
from the column have a life of any appreciable length. 
The number escaping will be increased by winds and 
eddy diffusion. In atmospheric electricity this matter 
has received but little consideration. It has been dis- 
cussed by Nolan [31]. 
The value of the effective recombination of small 
ions is usually taken as 1.6 X 107§ ce per sec for air at 
atmospheric pressure [6, p. 178]. However, Luhr and 
Bradbury [23] give a value of 1.23 x 1078, Sayers 
[38] gives 2.4 & 10-® and Nolan [31] gives a value of 
a xX Lo-*. 
Combination of Small Ions with Condensation Nuclei 
The theory of small-ion combination with condensa- 
tion nuclei or large ions has received less attention than 
has the theory of recombination. If all variables in the 
equations of small-ion balance were measured, it would 
be possible to determine the value of combination 
coefficients. Usually this is not done, but relations be- 
tween parameters are assumed. If it is asumed that 
equation (3) is equal to equation (4), it follows that: 
123 
No/M1 = 721/20, 
No/N2 = m2/N10, 
Ni/N2 = gvt1/noine. 
If we assume that N,; = N. = N, we obtain the rela- 
tionships: 
No/N = no/N20 = n12/N105 
M/N» = 720/10 = nor/N125 
which were assumed by Nolan and de Sachy [26]. 
Whipple [53] has deduced the following equations, which 
are sometimes used as an auxiliary relation between 
parameters: 
m2 = mo + Areky, (6) 
421 = 720 + Areks, 
where k; and ky represent the mobility of the positive 
and negative small ion, respectively. 
Almost every observer has used a different method 
of determining these combination coefficients. Gish and 
Sherman [9] gave a thorough discussion of these meth- 
ods together with a table of values prior to 1940. More 
recent values have been summarized by Parkinson 
[36], and Table III shows representative values. 
TasuE III. ComBinaTion ComFFICIENTS (in units of 10) 
70 1x9 un Moy 
Ge ASthvalWe er 2 phat eh cyan ee O45 || O20) Bo \) 2.6 
Greatestavaluen.acqcsss2 seo: G3 | 7G] 8.7% || Oi7 
IMIgchieyN WHI > coodocdescoseoecoe)| OG) Moll |) Bot |) 4005) 
It is not surprising that these values vary so widely 
when it is remembered that various methods of deter- 
mination have been used. Also it is not reasonable to 
expect that the combination coefficients would be pre- 
cise universal constants since they depend upon the 
nature (z.e., the mobility) of slow ions, which will vary 
with conditions and hence from place to place. Also, 
no notice is usually taken of the distribution of mobil- 
ities involved in the ions responsible for the destruction 
of small ions, nor is an allowance made for intermediate 
ions as distinct from large ions. 
Several investigators [32, 33] have found that the age 
of the large ion has an influence on the value of the 
combination coefficient, the coefficient becoming higher 
the older the nuclei. This is probably due to an increase 
in the size of the nuclei with age, owing to coagulation. 
Large-Ion Balance 
If we assume that a distinct group of large ions exists, 
then we can speak of their balance just as we do in the 
case of small ions. One method of formation of large 
ions is the process which has been mentioned above as 
one which destroys small ions, namely the fusion of a 
small ion with a neutral condensation-nucleus. The 
other process of destruction is the neutralization of 
charge by a small ion of opposite sign. There will also 
be a recombination term, similar to that for small ions, 
and a linear term ¢N to account for diffusion [30]. We 
can write Q for the formation of large ions by other 
