AIR CLEANSING BY CONVECTIVE STORMS
DONALD F. GATZ and A. NELSON DINGLE
The University of Michigan,
Ann Arbor, Michigan
ABSTRACT
Data relating to rain cleansing of the atmosphere have been gathered
throughout five convective rain-producing weather systems and analyzed
with respect to the concentrations of radioactivity in sequential sam-
ples of rain. For some of the rains, analyses of the pollen content of
sequential samples were also made. A consistent pattern of temporal
variation of concentration of both contaminants was observed in the
three rains of highest rainfall rate. This pattern, a rapid decrease of
concentration with time during the first portions of the rain, was absent in the two rains of lowest rainfall rate. The fact that rapid de-
creases in concentration occurred simultaneously for both radioactivity
and pollens is taken as evidence that both contaminants were removed
from the same air. Since pollens have their source at the earth’s surface, it is concluded that both radioactivity and pollens entered the con-
vective system from low levels via the convective updraft. It seems
possible that the absence of the rapid temporal decrease of concentra-
tion in the rains of low intensity may be due to the lack of a persistent,
organized updraft in these systems.
INTRODUCTION
Radiochemical analyses of samples of rainwater collected at fixed
ground stations from rain systems of all types have shown substantial
time variation of the concentration of radioactive substances in the rain.
These variations are present when one rainfallis compared with another
(e.g., by Walton, Fisher, and Krey') as well as from sample to sample
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