How does composition of air affect vapor saturation limit? Suppose we hold temperature, pressure, and gas composition (say, a standard atmosphere) constant.  Then we know that if we allow the water content of the air to vary it can range between 0 and some saturation limit S g/L.

How does that saturation limit vary with the composition of the air?  For example, does it depend on the molecular weight and proportions of the other constituents of the air?

Assuming the water (or whatever substance is in question) does not chemically react with any other constituents at that temperature and pressure are there other constituent chemical relationships that can affect the saturation limit?
I agree with "repurposer"'s comment that the saturation limit would be independent of the composition of the air.

It would just be a function of the partial vapour pressure of water.

$K_{p}=p_{H_2O}$, where $K_p$ is the equilibrium constant in pressure terms.

Consider this case similar to that of aqueous tension - it depends only on the temperature of the system, and not the other (non-reacting) components.
Whenever we want to find the pressure of the dry gas, i.e. pressure of the mixture of gases $-$ the pressure due to the water vapour.

Hope this helps!