# RRB Pg 117.  Saturation: When the air contains as much moisture as it can hold  The higher the temperature, the more moisture air can hold  If air.

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RRB Pg 117

 Saturation: When the air contains as much moisture as it can hold  The higher the temperature, the more moisture air can hold  If air temperature of moist air is lowered enough, the air will become saturated  If the temp falls below the dew point, water vapor usually turns into liquid water

 Moisture in the form of water vapor enters the atmosphere by evaporation, sublimation to a gas, and transpiration  Evapotranspiration: Evaporation and Transpiration together  Large amounts of energy are needed to change liquid water into water vapor during evaporation and transpiration, most of which comes from insolation  EUREKA!! EUREKA!!  Transpiration- a flashback to biology Transpiration- a flashback to biology

 Sling psychrometer: has two thermometers mounted so they can be slung through the air. One thermometer records air temp (dry bulb temp) and the other has a wet cloth which measures the wet bulb temp  Evaporation causes cooling  The drier the air, the greater the evaporational cooling, the greater the difference between the dry-bulb and wet- bulb temps  Use a dew point temperature table to determine the dew-point. ESRT pg 12

 Dew point is expressed using a unit of temperature (Celsius or Fahrenheit)  Dew point: the temp to which air must be cooled to become saturated  The only way to change the dew point is by adding or removing moisture from the air

 Locate the dry-bulb (air temperature) reading on the left hand side of the chart  Subtract the wet-bulb reading (measure of how dry or saturated the air is) from the dry- bulb reading  Locate the difference between the wet-bulb and dry-bulb readings across the top of the chart  Follow the horizontal row for the dry-bulb reading to the right until it meets the vertical column running down from the difference between the wet-bulb and dry- bulb readings

 If the dry-bulb temperature is 8 degrees Celsius and the wet-bulb temperature is 2 degrees Celsius, find the dew point  Note that the wet-bulb temp will always be the same or colder than the dry-bulb

 If the dry-bulb temperature is 26 degrees Celsius and the wet-bulb temperature is 25 degrees Celsius, find the dew point

 Relative humidity: the ratio of the amount of water vapor in the air (absolute humidify) to the maximum amount it can hold (moisture capacity)  Relative humidity is expressed as a percent of saturation  Air that is saturated = 100%  To determine RH, you need a sling psychrometer and a RH table- ESRT 12

 If the RH is 50%, the air could contain twice as much water vapor  As the temperature of the air approaches the dew point, the relative humidity approaches 100%

 Locate the dry-bulb reading on the left-hand side of the Relative Humidity chart  Subtract the wet-bulb reading from the dry- bulb reading  Locate the difference between the wet-bulb and dry-bulb readings across the top of the chart  Follow the horizontal row for the dry-bulb reading to the right until it meets the vertical column running down from the top

1. Find the RH when the dry-bulb temperature is 18 degrees Celsius and the wet-bulb temperature is 13 degrees Celsius 2. Find the RH when the dry-bulb temperature is 10 degrees Celsius and the wet-bulb temperature is 9 degrees Celsius

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