  The sulfur abundance is poorly known in most environments. Yet, deriving the
sulfur abundance is key to understanding the evolution of the chemistry from
molecular clouds to planetary atmospheres. We present observations of H$_2$S
110-101 at 168.763 GHz toward the Herbig Ae star AB Aur. We aim to study the
abundance of sulfuretted species toward AB Aur and to constrain how different
species and phases contribute to the sulfur budget. We present new NOrthern
Extended Millimeter Array (NOEMA) interferometric observations of the continuum
and H$_2$S 110-101 line at 168.763 GHz toward AB Aur. We derived radial and
azimuthal profiles and used them to compare the geometrical distribution of
different species in the disk. Assuming local thermodynamical equilibrium
(LTE), we derived column density and abundance maps for H$_2$S, and we further
used Nautilus to produce a more detailed model of the chemical abundances at
different heights over the mid-plane at a distance of r=200 au. We have
resolved H$_2$S emission in the AB Aur protoplanetary disk. The emission comes
from a ring extending from 0.67 (109 au) to 1.69 (275 au). Under simple
assumptions, we derived an abundance of (3.1$\pm$0.8)$\times$10$\rm ^{-10}$
with respect to H nuclei, which we compare with Nautilus models to deepen our
understanding of the sulfur chemistry in protoplanetary disks. Chemical models
indicate that H$-2$S is an important sulfur carrier in the solid and gas phase.
We also find an important transition at a height of 12 au, where the sulfur
budget moves from being dominated by ice species to being dominated by gas
species. Studying sulfuretted species in detail in the different phases of the
interstellar medium is key to solving the issue.
