  There are two important statements regarding the Trautman-Bondi mass at null
infinity: one is the positivity, and the other is the Bondi mass loss formula,
which are both global in nature. In this note, we compute the limit of the
Wang-Yau quasi-local mass on unit spheres at null infinity of an asymptotically
flat spacetime in the Bondi-Sachs coordinates. The quasi-local mass leads to a
local description of the radiation that is purely gravitational at null
infinity. In particular, the quasi-local mass is evaluated in terms of the news
function of the Bondi-Sachs coordinates.
