2Weight of Water Vapor in Air Relative Humidity = : The ratio of the air’s actual water content to its potential water vapor content at a given temperature.Relative HumidityWeight of Water Vapor in AirRelative Humidity =Weight of Potential Water Vapor in Air at SaturationBasically, relative humidity tells you how saturated the air is with water.
3A psychrometer is used to measure relative humidity. The dry bulb measures the air temperatureThe wet bulb gives a measure of how unsaturated the air is—the evaporation of water from the wet bulb lowers the temperature reading (and the evaporation depends on the saturation of the air)
4Dewpoint Temperature: The temperature the air would have to be cooled to saturate the air (causes water to condense
5The “Dry Bulb” Don’t let it fool you. It is just a thermometer. It measures the air temperature.Duh!20°C
6The “Wet Bulb” Has a little wet booty tied to the bottom. Gets cool when water evaporates.12°CWet Booty
7A Dry Day… A lot of moisture will evaporate. The wet bulb will be a lot cooler than the dry bulb.20°C20°C14°C12°C8°CDifference between wet bulb & dry bulb is 12 °C.
8A Humid Day… A little bit of moisture will evaporate. The wet bulb will not be much cooler than the dry bulb.20°C14°CDifference between wet bulb & dry bulb is 6 °C.
9Page 747 & 750 of your Handy Dandy Earth Science Reference Tables Warning #1: Be sure to READ the correct chart: DPT or RHWarning #2: Dew Point Temperature IS NOT “Difference between wet bulb and dry bulb”.Warning #3: The wet bulb temp IS NOT the DPT.
10Dry-bulb temperature is your air temperature. 20 °C