as air's capacity to hold water decreases, what happens to its relative humidity?

Answer 1

What I think you are asking is as temperature decreases, what happens to the relative humidity.

Since the saturation point of air with respect to water is largely linked to the temperature, and relative humidity (RH) is the ratio of the amount of water vapor compared to the saturation point of the air at that temperature RH will increase if everything else remains the same, that is, if the amount of water per unit volume of the air and the atmospheric pressure remains the same.

The RH will increase until the air is saturated with respect to water which means the RH becomes 100 percent.

After that, the water vapor will change phase into liquid or solid form (cloud/rain droplets, dew, frost, snow) depending on location and temperature to maintain the equilibrium with respect to water and the RH will remain at 100 percent until either temperature rises, more water vapor is removed or drier air is mixed into the air mass.

There are certain conditions where RH can go above the 100 percent mark such as during convective storms but in most cases, RH will not go above 100 percent.

Answer 2

Air's capacity to hold water decreases when the temperature of the air approaches the dew point temperature.When dew point temperature is reached,saturation occurs. In this condition, the Relative Humidity reaches 100 percent.
In other words,we can say that when the temperature decreases,the relative humidity increases (provided the moisture content is the same).
In fact,the relative humidity actually depends upon whether the air is saturated or not and does not depend upon the hotness or coldness of the air.

Answer 3

As long as the dew point stays the same while temperature is decreasing (losing its capacity to hold water) then relative humidity will increase.

Answer 4

In case of unsaturated air the realtive humidity will increase, with decrease in temperature(i.e decrease of air's capacity to hold water), keeping all other factors constant.

In case of saturated air, it will remain same i.e 100%

Answer 5

water has a vapor stress based on temperature. whilst the partial stress of water vapor in the ambience is comparable to the vapor stress, that defines one hundred% humidity. so relative humidity is the ratio of the partial stress of water in the ambience whilst in comparison with the theoretical vapor stress for the present temperature.