RELATIVE Sr CONCENTRATIONS IN SURFACE AIR
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of the HASL pot and column deposition stations to allow comparison of
rain samples with ground-level-air values. The air-sampling stations
have been grouped and averaged by rough latitude bands to facilitate
plotting the data on the graph.It is evident that the agreement between
stations and between sample types is very good in spite of the fact that
the analyses were carried out by a number of different laboratories,
Broadly, the data seem to follow the predicted slope of the ratio’s decay as indicated by the dashed line in the figure, It is not thought that
the slight deviations in April, May, and October are indicative of the
addition of older debris since the geographical spread of these sites is
so great. For instance, in May the grouping of data, which falls below
the line, consists of points from the entire network (9 to 76°N) and includes the Mauna Loa site at 155°W. From this spreadit is not likely
that the deviation is significant.
By late summer of 1963, the concentration of *°Sr in ground-level
air had decayed to levels where the measurement techniques were inadequate. Thus, in the absence of any Significant new injections of fis-
sion debris into the atmosphere, effective use of the ratio had ended by
the end of 1963.
Figure 5 illustrates the 88gr/Sr ratio for the data from the south-
ern nemisphere in 1963. The dashed line is the slope of the decay of the
ratio as defined by the data from the northern hemisphere, copied directly from Fig. 4. The fact that the ratios observed are lower than the
decay line through almost the entire year indicates that the debris in
the southern-hemisphere ground-level air was generally older than that
in the north. Qualitatively, as one would expect, values at all the sites
seem to be approaching the northern-hemisphere ratio later in the
year.
Two interesting relations can be pointed out in Fig. 5. The first
relates to ground-level transfer of debris across the equator. It can be
seen that the Guayaquil, Equador (about 2°S), point for April lies very
close to the northern-hemisphere value. The same situation was noted
in 1962 at Guayaquil and in 1959 for the sample from Quito, a site almost on the equator. In all these instances, the next site south, Lima,
Peru, at about 12°S, had a much lower value of ®Sr/"Sr. These data
suggest that in the northern-hemisphere spring, when air concentrations generally reach their maximum, some measurable transfer of air
occurs at ground level across the equator. Measurementsof the ®**Sr/
Sr ratio in precipitation have shown similar relations in the near-
equatorial regions.‘
The other interesting point that is suggested by the *Sr/"Sr ratios
of the southern-hemisphere air concerns the data from Chacaltaya,
Bolivia. This site located at about 17°S is of special interest because
of its unusual elevation, about 17,000 ft above mean sea level. In Fig. 5
the data from Chacaltaya are connected by a heavy line. Here it can be
(5%