  On-surface synthesis has recently emerged as an effective route towards the
atomically precise fabrication of graphene nanoribbons of controlled topologies
and widths. However, whether and to which degree structural disorder occurs in
the resulting samples is a crucial issue for prospective applications that
remains to be explored. Here, we experimentally identify missing benzene rings
at the edges, which we name "bite" defects, as the most abundant type of
disorder in armchair nanoribbons synthesized by the bottom-up approach. First,
we address their density and spatial distribution on the basis of scanning
tunnelling microscopy and find that they exhibit a strong tendency to
aggregate. Next, we explore their effect on the quantum charge transport from
first-principles calculations, revealing that such imperfections substantially
disrupt the conduction properties at the band edges. Finally, we generalize our
theoretical findings to wider nanoribbons in a systematic manner, hence
establishing practical guidelines to minimize the detrimental role of such
defects on the charge transport. Overall, our work portrays a detailed picture
of "bite" defects in bottom-up armchair graphene nanoribbons and assesses their
effect on the performance of carbon-based nanoelectronic devices.
