  In Zhang $\&$ Showman (2018, hereafter Paper I), we developed an analytical
theory of 1D eddy diffusivity $K_{zz}$ for global-mean vertical tracer
transport in a 3D atmosphere. We also presented 2D numerical simulations on
fast-rotating planets to validate our theory. On a slowly rotating planet such
as Venus or a tidally locked planet (not necessarily a slow-rotator) such as a
hot Jupiter, the tracer distribution could exhibit significant longitudinal
inhomogeneity and tracer transport is intrinsically 3D. Here we study the
global-mean vertical tracer transport on tidally locked planets using 3D
tracer-transport simulations. We find that our analytical $K_{zz}$ theory in
Paper I is validated on tidally locked planets over a wide parameter space.
$K_{zz}$ strongly depends on the large-scale circulation strength, horizontal
mixing due to eddies and waves and local tracer sources and sinks due to
chemistry and microphysics. As our analytical theory predicted, $K_{zz}$ on
tidally locked planets also exhibit three regimes In Regime I where the
chemical and microphysical processes are uniformly distributed across the
globe, different chemical species should be transported via different eddy
diffusivity. In Regime II where the chemical and microphysical processes are
non-uniform---for example, photochemistry or cloud formation that exhibits
strong day-night contrast---the global-mean vertical tracer mixing does not
always behave diffusively. In the third regime where the tracer is long-lived,
non-diffusive effects are significant. Using species-dependent eddy
diffusivity, we provide a new analytical theory of the dynamical quench points
for disequilibrium tracers on tidally locked planets from first principles.
