Final answer:
Saturation vapor mixing ratio depends on the vapor pressure and temperature of the substance. It is unaffected by the type of gas present but can be influenced by altitude due to changes in atmospheric pressure.
Step-by-step explanation:
The saturation vapor mixing ratio is primarily determined by water's vapor pressure and temperature. The equilibrium vapor pressure of a substance indicates the point at which its liquid and gaseous phases exist in balance and is a unique characteristic of that substance. This pressure is greatly influenced by the temperature, as it depends on the fraction of molecules with kinetic energy sufficient to escape from the liquid phase into the gas phase. This fraction exponentially increases with temperature, showcasing a strong temperature dependence. Furthermore, saturation vapor densities are independent of the kind of gas they're mixed with, such as helium or air, and remain valid as long as water's vapor pressure and temperature are controlled. However, these values can be affected by altitude on Earth due to changes in atmospheric pressure.