• Atmospheric pressure is the pressure exerted by gas particles in Earth’s atmosphere as those particles collide with objects.
  • A barometer is an instrument used to measure atmospheric pressure.
  • At sea level, a mercury column will rise a distance of 760 mm.
  • At higher altitudes, the atmospheric pressure is decreased and so the column of mercury will not rise as high.
  • On the summit of Mt.
  • Everest (elevation of 8848 m), the air pressure is 253 mmHg.
  • This marked decrease in atmospheric pressure results in much lower levels of oxygen.
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