How can the weather be below freezing AND 100% humidity?

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Doesnt the temperature mean that fog can’t be “humidity”?

Isn’t humidity moisture and doesn’t moisture crystallize into a solid form below 32 degrees?

In: Chemistry

5 Answers

Anonymous 0 Comments

There are two forms of humidity: relative humidity (%) and absolute humidity (grams of water/liter of gas). Something that is at 100% humidity means that it is holding as much water as possible, no matter how little that may be.

Anonymous 0 Comments

Humidity is water as a gas in the air. Water as a gas is ivisible that is why the bubbles when you boil water are clear, the contain water as a gas.
If you can see the water then it is a liquid or a solid not a gas For is liquid water dropples in the air.
I am avoiding to use the word vapor as it it is ofen missued. If you vape the white could you breath out is not vapour or atleas not the visible part. The visible part is small liquid dropplets.

So fog is not humid air but but liquid dropples of water in air. Fog is formed when humid air cool and the amount of water the air can contain is reduced and some of it consensate to liquid droples. So fog is formed by humid air that is cooled down but the visible part is not humid air.

Solid or liquid particle suspend in a gas is called a Aerosol. So the vible part when you vape, in fog or in a cloud is an aerosol not vapour. There can be vapour there too but that is the invisible gas.

Vapour is a gas at a temperatures where is can constensate bacl to a liquid without a change in temperature. Water as a gas between 0C( 32F) and 374 C( 705 F) is a vapour

Steam for example exits in two types:
Dry steam that is just water as a gas and it is invisible.
Wet steam that is a mixture of water as a gas and liquid droplets of water. This is the typical white stram you think about.

You can look this [Phase_diagram_of_water](https://en.wikipedia.org/wiki/Phase_diagram#/media/File:Phase_diagram_of_water.svg) and see tat water as a vapout is possible bewlow 0 (32F).

The pressure of the vater vapour that you can have depend on the temperature so the lower temperature the lower possible pressure of water as a gas is possible.

Relative humitity is the percetage of water currently as a gas and the max amount of possible at temperature. So if you heat upo a gas the relative humitity i will drop. If you cool it down it will increase.
If you cool it below the tempeatture is is saturated with water as a gas it will start to consesate to a liquid or deposit to a sloid. Freeizng is a liquid to a solid, the change from a gas to a solid is deposition.

So cold air is often 100% hunmid is becaue that do not require a lot of water So when air that was warer the hade lower humidity cool down the humidity increased untill you get to 100% when extra will become a liquid or a solid.

When you breath in cool air and heat it up in you nose etc the humidity drops so 100% humid air at 0C will be quite dry air in you body. So water in you nose etc will evaporate so it can dry it out even if it wats at 100% humidity when it was cold.

The result is that water can exist as gas at temperature is not longer can be a liquid. If you put ice in a container with air wil 0% humidity the result is that the ice will evaporate.

Anonymous 0 Comments

As the air temperature drops so does the ability of the air to contain water as a gas decreases. You need to understand the meaning of relative humidity. It is the percentage of the actual moisture present at a particular temperature relative to the saturation level at that temperature.

When the temperature of warm air decreases, because of the reduced water-holding capacity, there will be condensation of the excess water corresponding to the dew point. When that happens then the atmosphere is saturated and the RH is at 100%.

Anonymous 0 Comments

Ever go out in the morning and there’s frost on everything? That’s because the relative humidity was 100% and the temperature below freezing. This isn’t uncommon, because relative humidity goes up as the temperature goes down. The cold air can’t hold as much moisture as warm air can.

Fog is just a ground level cloud, and clouds can be tiny ice crystals just as easily as they can be droplets of water.

Anonymous 0 Comments

Fog is a [colloid](https://en.wikipedia.org/wiki/Colloid), being liquid water droplets suspended, rather than dissolved, in gaseous air. Humidity refers to the amount of water dissolved and held in solution in the air.