  We compute the polarized signal from atmospheric molecular oxygen due to
Zeeman effect in the Earth magnetic field for various sites suitable for CMB
measurements such as South Pole, Dome C (Antarctica) and Atacama desert
(Chile). We present maps of this signal for those sites and show their typical
elevation and azimuth dependencies. We find a typical circularly polarized
signal (V Stokes parameter) level of 50 - 300 \mu K at 90 GHz when looking at
the zenith; Atacama site shows the lowest emission while Dome C site presents
the lowest gradient in polarized brightness temperature (0.3 \mu K/deg at 90
GHz). The accuracy and robustness of the template are tested with respect to
actual knowledge of the Earth magnetic field, its variability and atmospheric
parameters.
