Measurements of the 225\,GHz atmospheric transparency with functionally identical tipping radiometers at Mauna Kea, the South Pole, and Chajnantor indicate periods of excellent observing conditions at all three sites. Conditions at Chajnantor and the South Pole are better than at Mauna Kea. The first quartile zenith transparency at Chajnantor and the South Pole are roughly equal. During the best conditions at Chajnantor, however, the zenith transparency is better than during the best conditions at the South Pole. Median conditions at Chajnantor and the South Pole are similar for observations near meridian transit when observing geometry is considered.***This memo has been revised. The new version can be viewed or downloaded from the following links: View a PDF of the revised version of ALMA Memo #334.
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