Brightness temperature rms as a function of frequency and astrophysical component for temperature (top) and polarization (bottom). For temperature, each component is smoothed to an angular resolution of 1deg FWHM, and the lower and upper edges of each line are defined by masks covering 81 and 93% of the sky, respectively. For polarization, the corresponding smoothing scale is 40′, and the sky fractions are 73 and 93%. We note that foreground rms values decrease nearly monotonically with sky fraction, whereas the CMB rms is independent of sky fraction, up to random variations. For reference, zodical light emission is roughly two orders of magnitude weaker than thermal dust emission in temperature.