Which property of air is the best measure for latent heat?

The best measure for latent heat in relation to air is the humidity ratio. The humidity ratio, also referred to as the moisture content, quantifies the mass of water vapor present in a unit mass of dry air. This property is essential for understanding latent heat because latent heat refers to the heat energy required for water to change its state, for instance, from liquid to vapor.

When considering processes like evaporation and condensation, the humidity ratio provides a clear insight into how much moisture is available in the air and thus how much energy (latent heat) is involved in these phase changes. High humidity ratios indicate more water vapor in the air, which directly correlates with the amount of energy associated with moisture transformation.

In contrast, while relative humidity accounts for the current amount of moisture relative to the maximum possible at a given temperature, it does not provide a direct representation of the moisture content itself. Dry bulb temperature indicates the actual air temperature and is not directly related to the moisture content's effect on latent heat. Enthalpy, while related to total energy, includes both sensible and latent heat, making it less specific for measuring latent heat alone when compared to the focused measure provided by the humidity ratio.