  We present a supermassive black hole (SMBH) mass measurement in the Seyfert 1
galaxy NGC7469 using Atacama Large Millimeter/submillimeter Array (ALMA)
observations of the atomic-${\rm [CI]}$(1-0) and molecular-$^{12}$CO(1-0)
emission lines at the spatial resolution of $\approx0.3$" (or $\approx$ 100
pc). These emissions reveal that NGC7469 hosts a circumnuclear gas disc (CND)
with a ring-like structure and a two-arm/bi-symmetric spiral pattern within it,
surrounded by a starbursting ring. The CND has a relatively low
$\sigma/V\approx0.35$ ($r\sim0.5$") and $\sim0.19$ ($r>0.5"$), suggesting that
the gas is dynamically settled and suitable for dynamically deriving the mass
of its central source. As is expected from X-ray dominated region (XDR) effects
that dramatically increase an atomic carbon abundance by dissociating CO
molecules, we suggest that the atomic [CI](1-0) emission is a better probe of
SMBH masses than CO emission in AGNs. Our dynamical model using the ${\rm
[CI]}$(1-0) kinematics yields a $M_{\rm
BH}=1.78^{+2.69}_{-1.10}\times10^7$M$_\odot$ and $M/L_{\rm
F547M}=2.25^{+0.40}_{-0.43}$ (M$_\odot$/L$_\odot$). The model using the CO(1-0)
kinematics also gives a consistent $M_{\rm BH}$ with a larger uncertainty, up
to an order of magnitude, i.e.\ $M_{\rm
BH}=1.60^{+11.52}_{-1.45}\times10^7$M$_\odot$. This newly dynamical $M_{\rm
BH}$ is $\approx$ 2 times higher than the mass determined from the
reverberation mapped (RM) method using emissions arising in the unresolved
broad-line region (BLR). Given this new $M_{\rm BH}$, we are able to constrain
the specific RM dimensionless scaling factor of $f=7.2^{+4.2}_{-3.4}$ for the
AGN BLR in NGC7469. The gas within the unresolved BLR thus has a Keplerian
virial velocity component and the inclination of
$i\approx11.0^\circ$$_{-2.5}^{+2.2}$, confirming its face-on orientation in a
Seyfert 1 AGN by assuming a geometrically thin BLR model.
