  The stability of graphene nanoribbons in the presence of typical atmospheric
molecules is systematically investigated by means of density functional theory.
We calculate the edge formation free energy of five different edge
configurations passivated by H, H$_2$, O, O$_2$, N$_2$, CO, CO$_2$, and H$_2$O,
respectively. In addition to the well known hydrogen passivated armchair and
zig-zag edges, we find the zig-zag edge saturated by oxygen atoms to be
particularly stable under atmospheric conditions. Saturation by oxygen leads to
the formation of metallic states strictly localized on the oxygen atoms.
Finally, the vibrational spectrum of the hydrogen and oxygen passivated ribbons
are calculated and compared.
