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!! 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