On a crisp, cold day, there's visible evidence of something we all know, but usually forget in days of warmth. That cloud appearing in front of our faces as we exhale is water--water changed from vapor into tiny, condensed droplets upon contact with the chill air. Of course, the same moisture-laden air is exhaled in warm weather, too, but sneaks out unseen.
That the air we exhale is full of water is one of the reasons for heat
stress in our desert. We tend to think of the water lost by sweating--and indeed this
is the most critical factor, but even under non-stressful conditions, we lose somewhere
around a cupful a day through respiration. In dry desert air, summer or winter, it may
well be more—enough to make a life or death difference. Why not just breath dry air in
and out instead of saturating it with water in our lungs? Simple. If the surface areas
of our lungs were not wet, oxygen couldn't pass from the air through the lung
tissues into the blood. Can you say suffocate?
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.