Water Vapour and Moisture in the Air Humidity

We know there is water in the air! Clouds Dew on grass in the mornings Fog Humidity

What creates water vapour? Most of the water vapor in the air that comes from water that evaporates into the air from the oceans, especially warm oceans. Water also evaporates into the air from vegetation. Extremely humid air, however, comes from over warm oceans.

Saturation When there is as much water vapour in the air as possible at any given temperature, we say the air is saturated Humidity = the amount of water vapour in the air Relative humidity = expressed as a percent (out of the max amount of water vapour the air will hold)

Moisture in the Air Cold air can hold less moisture then warm air Therefore when the air temperature is high, the amount of water vapour can be high Moist air takes a bit longer to cool then drier air

What happens in the summer when you bring a cold drink outside? Lets say the air temperature is 26 degrees Celsius. When the air is this warm it can hold a lot of water vapour When you bring out the cold glass, the air directly next to the glass becomes colder. This colder air can not hold as much water vapour as the warmer air, so the water “falls out” It “falls” onto the glass because that is a surface for the water droplets to form on

Q: Why does warm air hold more moisture than cold air? In basic terms, what happens is that the warmer the air the faster all of the molecules in it, including water vapor, are moving. As the air cools the molecules slow down and more of them are likely to be going slowly enough to be "captured" by water that is already liquid.

Q: Why is humidity so low in the winter, compared with the summer? A: Humidity is the amount of water vapor in the air. During the summer, warm, moist air flows north over the USA from the Gulf of Mexico. The warm water evaporates into the air, making it more humid. This is known as a maritime tropical air mass. In the winter, cold, dry air flows south from Canada and Alaska. This air stays particularly dry since it originates over land and is known as continental polar air. In the winter, the moisture content is lower and therefore less humid.

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