CHLORIDE-SULFATE RELATIONSHIPS IN THE ATMOSPHERE 253 
cipitation. It will, however, be in some degree de- 
pendent on the frequency of precipitation. 
The findings of Byers and others [1957], 
among others, make it clear that particulate 
matter sampled near the surface of the Earth 
may not be representative of that aloft. It is 
more likely to represent local influences, and 
less likely to show marine influence, than sam- 
ples taken at higher altitudes. Thus raimout, rep- 
resenting as it does the mean concentration in a 
layer of air some thousands of feet thick, may 
differ markedly in composition from surface air; 
it should be more representative of the atmos- 
phere as a whole. This is especially apparent im 
the two sets of urban data in the present study. 
The interpretation—The data, with sulfate ex- 
pressed as sulfur equivalent, were fitted to best 
regression lines on logarithmie paper by the 
method of least squares. Thus all the regres- 
sions had the form 
(Cl) = .a(s)? (1) 
where (Cl) is the concentration of chloride in 
appropriate units, (S) is the concentration of 
sulfate computed as sulfur in the same units, 
and a and b are constants. Table 1 gives the 
values of a, 6, and the correlation coefficient 7 
for all cases in which significant correlations were 
obtained. 
A particular sample of airborne particulate 
matter, however taken, will contain chlorine and 
sulfur compounds of very local origin, together 
with substances which have traveled great dis- 
tances. A reasonable physical model is that of 
the atmosphere as a great reservoir, charac- 
terized by a certain mean ratio of chlorine to 
sulfur. At any point within this reservoir, how- 
ever, local perturbations may result in a sam- 
ple composition very different from the mean. 
However, from the viewpoint of a particular 
sampling location, it is perhaps simpler to con- 
sider the mean atmosphere and the various local 
influences on an equal footing. This mathemati- 
cal model of the sample as the result of a num- 
ber of ‘sources’ has the advantage for purposes 
of this paper of involving less prejudgment con- 
cerning the over-all mechanism. Further study 
should be made before a mechanism can be set 
forth with confidence. Thus three ‘sources’ will 
be considered: the oceans, the mean atmosphere, 
and human activity. 
The direct marine contribution contains chlo- 
ride equal roughly to 21 times the mass of sul- 
TaBLe 1—Summary of regression 
data; order of increasing a 
Site ey | Nei r 3 
| E 
| 
Champaign, Illinois | 0.401 .11|0.77| P 
Mt. Hamilton, California | 0.60)0.63 0.62) A 
San Nicolas Island, Califor- | 1.22)1.02)0.57) A 
nia | 
Station November 1.85/0.73/0.47| A 
Bonn, Germany 2.12|0.55)0.55) A 
Valentia, Ireland 2.82/1.30/0.91) R 
Point Piedras Blancas, Cali- | 6.20)1.20/0.71) A 
fornia 
South East Farallon Island, | 6.241.050.57) A 
California 
Valentia, Ireland 1.7 (1310.90) 
Kinnvika, Spitsbergen 28.6 |0.92/0.92) A 
61.5 (0.54 0.59) R 
«Type of analysis: P = 
rainout; A = air. 
precipitation; R = 
fur. Thus its composition may be represented as 
(Cl) = 21 (5) (2) 
The total atmospheric loading has been deduced 
by Eriksson [1959]. From his figures, one obtains 
(Cl) = 148 (S) (3) 
for the chlorine-sulfur relationship. The third 
component, man’s own products, contributes, 
for practical purposes, only sulfur to the atmos- 
phere. It may thus be taken as a relationship of 
the form 
(Gh =k (4) 
that is, for a given station, the chloride level 
will be relatively constant, as fixed by that en- 
tering the area, but sulfur is indeterminate and 
independent of chloride. Thus the mean chloride- 
sulfate relationship for any locale will reflect all 
three ‘sources.’ (It should also follow that the 
world-wide average of all such determinations 
should be identical with the above ‘mean atmos- 
phere’ relationship (Eq. 3), within the accuracy 
of Eriksson’s figures.) 
Turning to the actual data, it can be seen that 
Kinnvika (Fig. 1) is the most truly ‘maritime’ 
station. Both air and rainout figures are for 
practical purposes identical in composition with 
sea water. The precipitation itself varies so much 
less than that of most stations that 1t may well 
be constant within the errors of the measure- 
ments. 
Station November (Fig. 2), in contrast, is 
