Humidity and Dew Point

Foldable Make a two flap foldable one side Relative Humidity and the other side Dew Point Should Contain What it is How it is measured How each is calculated Where does saturated fit into the mix

 Humidity refers to the amount of moisture (water vapor) in the surrounding air.

 RATIO of the amount of moisture in the air compared with the amount of moisture the air can hold at that temperature and pressure.  Expressed as a percentage.

 Relative humidity varies with temperature because warm air is capable of holding more moisture than cool air. State of the Atmosphere –If the temperature of an air parcel increases and no additional water vapor is added, its relative humidity decreases. –If more water vapor is added to the parcel, its relative humidity increases.

 Relative humidity is expressed as a percentage. State of the Atmosphere –If a certain volume of air is holding as much water vapor as it possibly can, then its relative humidity is 100 percent. –If that same volume of air is holding half as much water vapor as it can, its relative humidity is 50 percent, and so on.

 The state when air contains the maximum quantity of water vapor that it can hold at any given temperature and pressure.  The amount of water vapor required for saturation depends on temperature  When saturated, warm air contain more water vapor than cold air.

 If the air is at 90% relative humidity, sweat will not evaporate into the air.  As a result, we feel much hotter than the actual temperature.  If the relative humidity is low, we can feel much cooler than the actual temperature.  because our sweat evaporates easily, cooling the body.

The length of a strand of human hair changes with different relative humidities. As the relative humidity increases, hair becomes longer, and as the humidity drops it becomes shorter. On very humid days, your hair actually becomes longer and this extra length causes the frizziness that gives us bad hair days.

 Sling Psychrometer  It consists of two identical mercury thermometers:  Evaporating water from the wick absorbs heat from the thermometer bulb, causing the thermometer reading to drop.

Find the difference between the DRY bulb and the WET bulb on the two thermometers Use the Relative Humidity Table Where the DRY bulb temperature and the DIFFERENCE between the two thermometers intersects…is your relative humidity. Example – If the DRY bulb temperature reading is 22°C and the DIFFERENCE between the two thermometers is 6°…the relative humidity is 53%

1.Dry bulb = 12° Wet bulb = 7° 2. Dry bulb = 22° Wet bulb = 20° 3. Dry bulb = -10° Wet bulb = -7° 48% 83% 0%

Why Care about Relative Humidity? If we can’t sweat…we could overheat and DIE!!

 The temperature that air would need to cool to condense the water vapor into liquid water.

Dew Point is determined the SAME EXACT WAY that Relative Humidity is calculated…a Sling Psychrometer. You just use a DIFFERENT chart… the DEWPOINT chart..DUH!! 1.Dry bulb = 12° Wet bulb = 7° 2. Dry bulb = 22° Wet bulb = 19° 1° 17°

Dew point is the temperature air must be cooled to reach saturation.  Below this temperature, water condenses  Raising temperature 10 degrees double vapor capacity.  Cooler temperatures reach dew points more easily