|MadSci Network: Earth Sciences|
There are really two aspects to answering this question. The first is that the atmospheric pressure decreases with altitude. At higher altitudes, the "weight" of air above you is less, so the pressure is lower (just like the pressure is higher at the bottom of the ocean). This is discussed here: http://w ww.pbs.org/wgbh/nova/everest/exposure/pressure.html At the top of Mount Everest, the atmospheric pressure is about one-third of what it is at sea level, as discussed on these two pages http://www .pbs.org/wgbh/nova/everest/exposure/higher.html http://www.mos.org /Everest/exhibit/physiology.htm These also discuss some of the physiological effects of the decrease in pressure. The second aspect is the effect of atmospheric pressure on the boiling temperature. Boiling happens when the vapor pressure exerted by the water equals the atmospheric pressure. So boiling is easier (can happen at lower temperatures) when the pressure is lower, as explained here: http://www.iapws.org/faq1/boil.ht m So yes, altitude matters for boiling. At sea level, water boils at approximately 100 degrees Celsius. In the Denver area where I live, the atmospheric pressure is about 83% of that at sea level, and water boils at about 95 degrees C. Atop Mount Everest, it is about 34% of sea level, which translates into boiling at about 72 degrees C. Allan Harvey, email@example.com "Don't blame the government for what I say, or vice-versa."
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