1. Moisture in the Atmosphere
Chapter 18

2. Humidity 18.1
Brain Pop: Humidity

3. Humidity: the amount of water vapor in the air

4. The warmer the air, the more H2O vapor it can hold!
Saturated: The state of air that contains the maximum quantity of water vapor that it can hold at any given temperature and pressure.
The warmer the air, the more H2O vapor it can hold!

7. Expressed as a percentage!
Relative humidity: the ratio of the air’s actual water-vapor content compared with the amount of water vapor air can hold at that temperature and pressure
Expressed as a percentage!
Relative humidity=specific humidity X capacity (saturated)

8. Dew Point: The temperature that air must be lowered to in order for water vapor to condense

9. moist air dry air High dew point temperature =
Any time the air temperature drops below the dew point, dew, clouds, or fog will form
moist air
Low dew point temperature =
dry air
If dew point is below freezing, frost will form
For every 10oC increase in temperature, the amount of water vapor needed for saturation doubles

10. Psychrometer: instrument used to measure relative humidity
Measuring Humidity
Psychrometer: instrument used to measure relative humidity
Works on principle that evaporation causes cooling
2 thermometers…wet-bulb and dry-bulb
Readings show how dry the air is
How to measure relative humidity

11. Can YOU measure Relative Humidity?!
Let’s practice!