Enter an elevation and click "Calculate" to
display the percent difference between air pressure at sea-level and air pressure at some
elevation.
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The air pressure in Denver is approximately 17% less than
that of sea-level. That's 17% less volume of air available to your lungs.
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| Have you ever wondered what the difference is between
training at sea-level and at some elevation or why it can be difficult to breathe while
climbing a 14ner. Then read on. You've often heard that the air is "thinner" at
elevation, in reality its lighter, and less compressed. |
| The air's pressure is caused by the weight of the air
pressing down on the Earth, the ocean and on the air below. Earth's gravity, of course,
causes the downward force that we know as "weight." Since the pressure depends
on the amount of air above the point where you're measuring the pressure, the pressure
falls as you go higher and volume per cubic foot decreases. The "weight" of the
air above you compresses the volume, thus the lower you are the more compressed the air is
and the more oxygen you can take in per breath. |
Pressure decreases with altitude. As you go higher in
the air, the atmospheric pressure decreases. The exact pressure at a particular altitude
depends of weather conditions, but a couple of rules of thumb (approximations) and a
formula give you a general idea of how pressure decreases with altitude. A rule of thumb
for the altimeter correction is that the pressure drops about 1 inch of mercury for each
1,000 foot altitude gain. If you're using millibars, the correction is 1 millibar for each
8 meters of altitude gain. These rules of thumb work pretty well for elevations or
altitudes of less than a two or three thousand feet. Here's the formula if you want a more
precise answer: Pressure decreases with height in the first 100 kilometers above the
earth's surface according to the formula P(z)=P(sea level)*exp(-z/H). P(z)= pressure at
height z, P(sea level)= sea level pressure(~1013 millibars), z= height in meters, H= scale
height( to keep the formula simple, we're using 7 kilometers for the scale height). Since
the formula is in metric units, you'd have to convert an altimeter setting, which is
always given in inches of mercury in the U.S., to millibars, using the conversion: one
millibar is equal to 0.02953 inches of mercury In all the formula, / means to divide, *
means to multiply, "exp(-z/H) means to divide minus z by H and then take the inverse
of the natural log of the answer. The standard rules of algebra apply.
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