Definition of "atmospheric pressure" []

• Pressure caused by the weight of the atmosphere. At sea level it has a mean value of one atmosphere but reduces with increasing altitude. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "To stay conscious in the low atmospheric pressure of these extreme heights, the crew would have needed pressurized pure oxygen in their lungs and the PEAPs only supplied sea levelair, a mixture of about 80 percent nitrogen and 20 percent oxygen."
• "A standard altimeter could not tell the astronauts when they reached their perilune because an altimeter was an instrument that determined altitude based on changes in atmospheric pressure and the Moon has no atmosphere."
• "When his near-vertical climb reached 90,000 feet, atmospheric pressure fell to a scant 6 millibars, about 1 percent of the pressure at sea level."