At that time, suspicions that rain was the cause were confirmed with observations of high levels of sulfuric acid in rainwater.
(rain; was; the cause) (suspicions that rain was the cause; were confirmed; with observations of high levels of sulfuric acid in rainwater; T:At that time)
rain suspicions that rain was the cause
was were confirmed
the cause
with observations of high levels of sulfuric acid in rainwater T:At that time