Dear Tom,

Why doesn’t air pressure cause problems the way temperature does?

Arnold Ress, Des Moines, Iowa

Dear Arnold,

Air pressure is a benign weather phenomenon in the sense that its effects on the human body are minor within the limits that air pressure varies. Chicago’s air pressure extremes are 30.98 inches (Feb. 16, 1989) and 28.70 inches (Mar. 12, 1923). The difference, 2.28 inches, represents only about one pound per square inch, or an elevation change of 2,160 feet. Air pressure, a measure of the weight of air, is determined by the amount of air extending up to the “top” of the atmosphere. A barometer measures the number of inches of mercury in a vertical tube that weighs the same as the air pressure, 29.92 inches at sea level, or 14.7 lbs. per square inch.