our proposed visit to beijing 28th dec to 2nd jan.

Hey, the flights get cancelled because of the snowfall and haze. While during your travel period, the weather can be fine and the sky would be very likely to be clear, so it is ok to travel. The only concern is the low temperature. It will be cold then, and the temp can be much lower, perhaps -7C or so. If you really cannot bear it, skip the city then.