We present two main contributions. First, we provide optimal stability
estimates for advection-diffusion equations in a setting in which the velocity
field is Sobolev regular in the spatial variable. This estimate is formulated
with the help of Kantorovich–Rubinstein distances with logarithmic cost
functions. Second, we extend the stability estimates to the advection-diffusion
equations with velocity fields whose gradients are singular integrals of
functions entailing a new well-posedness result.