  In protoplanetary disks, atomic carbon is expected to originate from the PDR
at the disk surface where CO is dissociated by UV photons coming from the
stellar, or external interstellar, radiation field. Even though atomic carbon
has been detected in several protoplanetary disks, there is a lack of spatially
resolved observations of it. For HD 163296 protoplanetary disk, we aim to
obtain both radial and vertical structure of [CI]$={^3}{P_1} - {^3}{P_0}$ line
emission and perform the first direct comparison of this tracer with optically
thick line emission $^{12}$CO $J=2-1$. We used archival ALMA data for
[CI]$={^3}{P_1} - {^3}{P_0}$ and previously published ${^{12}}$ CO $J=2-1$ data
in HD 163296. Through the software of disksurf we extracted the vertical
structure, meanwhile radial profiles were obtained directly from imaging. Brand
new DALI modelling was employed to perform direct comparison to the data. We
found that these tracers are collocated radially but not vertically, where
$^{12}$CO $J=2-1$ emission is, on average, located at higher altitudes, as it
is also the case for other tracers in the same disk. Due to this difference in
vertical height of the emission, the optically thick $^{12}$CO $J=2-1$ emission
line appears to trace the highest altitudes, despite the expected formation
mechanism of [CI] in the disk. The latter phenomena may be due to efficient
mixing of the upper layers of the disk, or UV photons penetrating deeper than
we expected.
