1. 1 ATMOSPHERIC PRESSURE & DENSITY

2. 2 The denser the atmosphere…  the greater its weight, and  the greater its air pressure.

3. 3 atmospheric pressure - a.k.a.; barometric pressure or air pressure. the pressure due to the weight of the overlying atmosphere. diagram

4. 4 Measurement of and Changes in Air Pressure The instrument that is used to measure air pressure is a… barometer. Mercury barometer

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6. 6 Air pressure is measure in either 1)Millibars 2)Inches

7. 7 To convert from millibars to inches of mercury use the Earth Science Reference Tables, page 13. Examples. 1)976.0 mb = 2)1001.0 mb = 3)30.00 inches = 4)29.09 inches = 28.82 inches 29.56 inches 1016.0 mb 985.0 mb

8. 8 Lines drawn on a weather map that connect locations that have the same barometric pressure are called… isobars

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13. 13 The Effect of Temperature on Air Pressure. As the temperature of the air increases, the air expands and its density and pressure decrease. example; Hot Air Balloon

14. 14 The Effect of Water Vapor on Air Pressure. The greater the amount of water vapor in the air, the lower the air density and pressure. molecular weight water (H 2 0) 1(2) + 16 = 18 molecular weight air Nitrogen (N 2 )Oxygen (O 2 ) 14 (2) = 2816 (2) = 32 one molecule of water weighs less than one molecule of air.

15. 15 The Effect of Altitude on Atmospheric Pressure. As altitude or elevation increases, atmospheric density and pressure decrease. diagram

16. 16 less pressure more pressure

17. 17 SUMMARY; As either altitude, temperature or moisture content increases, air pressure decreases.