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Breath Outside and Humidity
Name: Eric
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
Seeing your breath when you are outside lets you know that
it is indeed cold..! The reason you can "see" your breath is due to
the water vapor in your breath. When you breathe in, water vapor is
added to the air by your lungs, along with the carbon dioxide from
your body. When your breath leaves your warm body, and comes in
contact with the cold air, it is immediately cooled. As it cools,
the water vapor, which you cannot see, condenses into tiny water
droplets, very much like the droplets in a cloud or fog. The
particles are so small that they cannot be identified by the eye
either, but we see the light reflected off them, much like smoke
from a cigarette. So we really do not see our "breath" at all, but
we see the condensed water vapor droplets in our breath. As soon as
the droplets form, they continue to mix with the outside air, and
are quickly evaporated in the drier air, and your "breath"
disappears. Wendell Bechtold, meteorologist Forecaster, National
Weather Service Weather Forecast Office, St. Louis, MO
Does your breath fog more or less if there is less humidity in the
cold air? it would seem that if what we see is condensed water vapor
in our breath then the less water vapor in the outside air, the more
our condensation would show?
Replies:
Actually, the opposite is true. Humid air conducts heat away from the breath
more efficiently causing it to condense faster and in greater volume. Because
high humidity slows the evaporation, the "breath" persists longer.
R. W. "Bob" Avakian
Instructor
Oklahoma State Univ. Inst. of Technology
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Update: June 2012
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