  We propose to use the unique event topology and reconstruction capabilities
of liquid argon time projection chambers to study sub-GeV atmospheric
neutrinos. The detection of low energy recoiled protons in DUNE allows for a
determination of the leptonic $CP$-violating phase independent from the
accelerator neutrino measurement. Our findings indicate that this analysis can
exclude several values of $\delta_{CP}$ beyond the $3\sigma$ level. Moreover,
the determination of the sub-GeV atmospheric neutrino flux will have important
consequences in the detection of diffuse supernova neutrinos and in dark matter
experiments.
