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Dew Point and Relative Humidity

Dew Point and Relative Humidity. What is Humidity?. Humidity- the amount of water vapor (WV) in the air Relative Humidity- the % of WV in the air compared to the maximum amount of WV the air can hold at a certain temp. Weather.com. http://www.weather.com/weather/today/Livingston+NJ+07039.

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Dew Point and Relative Humidity

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  1. Dew Point and Relative Humidity

  2. What is Humidity? • Humidity- the amount of water vapor (WV) in the air • Relative Humidity- the % of WV in the air compared to the maximum amount of WV the air can hold at a certain temp.

  3. Weather.com http://www.weather.com/weather/today/Livingston+NJ+07039

  4. True or False? WARM air can hold more water vapor than COLD air. TRUE! Warmer air is less dense, and therefore, has more room for water molecules

  5. WARM AIR COLD AIR Smaller volume, less room for H2O Larger volume, more room for H2O

  6. Calculating relative humidity: If 1 cubic meter of air at 60°F can hold 8 grams of water vapor and it currently holds 6 grams, what is the relative humidity of the air? 6 g ÷ 8 g = 0.75 = 75% rel. humidity

  7. How is relative humidity measured? • Relative humidity is measured with an instrument called a psychrometer

  8. What is saturation? Saturation- The point at which air is “full” of water vapor • R.H. = 100% • Water vapor condenses

  9. What happens when the air is saturated? DEW POINT - the temperature at which the air is saturated and condensation begins. • If DP is above freezing: liquid water (dew) • If DP is below freezing: solid water (frost)

  10. Dew = air reaching condensation point ABOVE freezing http://apollo.lsc.vsc.edu/classes/idm3020/tut_folder/nick_tutorial/Images/grass-dew.jpg

  11. Frost- air reaches condensation point BELOW freezing http://www.donnan.com/images/frost2.jpg

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