& 28 $\pm$ 1 & 6.18\
J192345.73 & 0.117 & 0.0032 & 47 & 76 & 1.36 $\pm$ 0.002 & 4.84 $\pm$ 0.266 & 28 $\pm$ 2 & 6.18\
J203901.04 & 0.221 & 0.0066 & -8 & 2 & 1.05 $\pm$ 0.002 & 1.44 $\pm$ 0.165 & 73 $\pm$ 8 & 8.14\
DR21 & 0.297 & 0.0077 & -8 & 2 & 1.38 $\pm$ 0.002 & 2.92 $\pm$ 0.167 & 47 $\pm$ 3 & 8.05\
J205658.56 & 0.935 & 0.051 & -5 & 9 & 3.67 $\pm$ 0.025 & 12.0 $\pm$ 1.729 & 31 $\pm$ 5 & 7.38\
J205703.98 & 1.604 & 0.051 & -4 & 5 & 5.10 $\pm$ 0.033 & 11.7 $\pm$ 1.915 & 44 $\pm$ 7 & 7.37\

Beam Size Effect {#subsec:beam}
----------------

The beam sizes are $\sim$4 arcmin at C-band and $\sim$1.3 arcmin at Ku-band, respectively. The temperature difference between the microwave background (2.73 K) and the excitation temperature of the collisionally cooled (@1975ApJ...196..433) H$_2$CO lines is about 1.5 K, as derived from our non-LTE calculations. For a cloud fully filling the beam, and being optically moderately thin, e.g. $\tau = 0.3$, this would result in about 0.5 K across that part of the beam not 