  Atmospheric emission is a dominant source of disturbance in ground-based
astronomy at mm wavelengths. The Antarctic plateau is recognized to be an ideal
site for mm and sub-mm observations, and the French/Italian base of Dome C is
among the best sites on Earth for these observations. In this paper we present
measurements, performed using the BRAIN-pathfinder experiment, at Dome C of the
atmospheric emission in intensity and polarization at 150GHz, one of the best
observational frequencies for CMB observations when considering cosmic signal
intensity, atmospheric transmission, detectors sensitivity, and foreground
removal. Careful characterization of the air-mass synchronous emission has been
performed, acquiring more that 380 elevation scans (i.e. "skydip") during the
third BRAIN-pathfinder summer campaign in December 2009/January 2010. The
extremely high transparency of the Antarctic atmosphere over Dome Concordia is
proven by the very low measured optical depth: <tau_I>=0.050 \pm 0.003 \pm
0.011 where the first error is statistical and the second is systematic error.
Mid term stability, over the summer campaign, of the atmosphere emission has
also been studied. Adapting the radiative transfer atmosphere emission model
"am" to the particular conditions found at Dome C, we also infer the level of
the PWV content of the atmosphere, notoriously the main source of disturbance
in millimetric astronomy (<PWV>=0.77 +/- 0.06 + 0.15 - 0.12 mm). Upper limits
on the air-mass correlated polarized signal are also placed for the first time.
The degree of circular polarization of atmospheric emission is found to be
lower than 0.2% (95%CL), while the degree of linear polarization is found to be
lower than 0.1% (95%CL). These limits include signal-correlated instrumental
spurious polarization.
