Ground-based measurements of the Cosmic Background Radiation (CBR) are hampered by emission from atmospheric O-2 and water molecules. We performed multifrequency measurements of the atmospheric emission in the 1-90 GHz spectral range from two high-altitude sites (White Mountain, California, and South Pole, Antarctica). A power spectrum analysis of our data shows variations of the atmospheric antenna temperature which exceed, on time scales of a few hours or more, those expected from radiometer noise and changes in water column density. When combined with real-time measurements of the local profiles of atmospheric pressure, temperature and humidity, our results indicate variations of order 10% of the O-2 emission (both resonant and non-resonant components) on time scales of hours to days, driven by the evolution of the atmospheric pressure profile. These oxygen emission fluctuations appear significantly larger than previously expected, and may affect ground-based CBR experiments.
