Why does the relative humidity of places differ? does whether it is an indoor area or outdoor area affect it?

Question

From the data i have, it seems that indoor areas have higher relative humidity readings than outdoor areas.

Answer 1

Most likely, with all other things being equal, the humidity is different. Relative humidity (RH) is relative to the temperature, thus the name. If the temperature is different between inside and outside the RH will be different even though the amount of water per volume may be the same. I get the feeling you have air conditioning and it is currently running. AC by design will remove water from the air but since it can be much warmer outside than inside the RH will be higher inside due to the decreased amount of water needed for the air to become saturated. RH flutuates so much as temperature increases or decrease is why most forecasters (meteorologists) pay no attention to it other than to report it to the media who use it and publish it. Most forecasters use either dew point (which is what most often reported in the observations from weather stations) or if things are really critical mixing ratio which is a ratio of amount of water to amount of air usually express as grams per kilogram. The advantage of using dew point or mixing ratio is that it does not change as temperature increases or decreases and is a more usable measure of amount of water in the air. You can say you have 100 percent RH but if I don't know the temperature that the reading was taken at, I can not tell you how much water is in the air since RH is the ration of the amount water in air compared to the amount of water required for the air to become saturated. The amount of water to saturate the air is dependent on the temperature. But if you tell me the dew point is 20 degrees C. I know exactly how much water is in the air and I don't need to know the temperature.

Answer 2

Relative Humidity is a function of air temperature and dew point temperature. When they are equal, then the relative humidity is 100% and the further they are apart the closer they tend towards 0%.

So if the dew point temperature was the same between 2 different places, then the place with the warmer air temperature would have the higher Relative Humidity. So often indoors is often more humid during the daytime and less humid at night time when comparing to outside.

Of course heating and cooling devices would make a huge difference too, so presume that none of that is taking place.

Answer 3

Indoor humidity is affected by outdoor humidity.
Even with controlled humidity, it will always be a bit erronous.
Since outdoor humidity can quickly change/vary due to winds etc, indoor humidity will also change.

The best example of this, is dying carpet and fabrics.
The mills must have artificially controlled humidity. Humidity affects their ability to maintain a standard color in different runs.
Even with controlled humidity, and all the high tech computers, it can change during the dying process, affected by any change outdoors. The water temperture and dye amounts are fairly controlled, but water temp is affected by humidity changes.

This is the reason that no two runs are of the same "Dye Lot", and two or more runs cannot be matched in shades of the same color.

Answer 4

Cold frigid air can hold very little moisture, when you bring that dry air into your house and warm it up it is still very dry. Relative Humidity is based on air temperature, warmer air can hold more moisture, so air that is saturated at -10 will be drier (lower RH) when you bring it indoors and heat it to room temperature. The opposite is true in the summer, when warm air is cooler by air conditioning and indoor climate can become quite moist.