## Condensation trail ain’t on my bucket list

Things tend to go from where they are to where they ain’t. (I know. Ain’t, ain’t a word. But sometimes the shock value of poor English makes something more memorable.) This statement is true of all material matter, and the process is called diffusion. All physical things diffuse. Just at different rates.

It is not necessarily true for abstractions. If you are waiting for knowledge to go from somewhere else into your head, you will remain unknowledgeable for a long time.

I got to thinking about diffusion because of my wife. She said, “Look at where several contrails from jets are crossing at almost the same point in the sky.” Unfortunately, when I looked up, I almost wrecked the car and killed us both. See, things tend to go from where they are to where they aren’t, especially if you aren’t watching where you are going!

A brief discussion then ensued as to whether or not I should be a better driver, or she should be less of a distraction. Well, define “brief discussion.”  Anyway, hands down, I won. She has been nothing but a distraction to me since the day we met.

Of course, the discussion also left me considering if I could determine when each contrail was made based upon the varying widths of the contrails and the diffusion rate.

If you can remember the distant past, say about last December, you might recall that when you breathed out, the warm moist air from your lungs condensed in the cold air outside, and you left a contrail. The word “contrail” stands for “condensation trail.” Of course, your contrail dispersed within seconds because the water evaporated and diffused into the surrounding air.

If I had a bucket list, I’d like to go someplace where the outside temperature is minus 40 degrees Fahrenheit, which incidentally is the same as minus 40 degrees Celsius. At this temperature, when someone breathes out, the vapor condenses and freezes. It leaves behind a cartoon balloon hovering about your face. That would be so cool! Unfortunately, breathing air that is minus 40 degrees anything is pretty dangerous. That’s one reason I don’t have a bucket list. They tend to be risky.

Anyway, when a jet engine burns fuel, or carbons, hydrogens and oxygens all mixed up together, the hydrogens and oxygens make water vapor. At a sufficiently high elevation, the water vapor not only condenses, but freezes, because it is minus 40 degrees Fahrenheit or Celsius up there. The ice can’t evaporate because it’s frozen, and the ice can’t melt because it’s minus 40 degrees. You end up with tiny little ice cubes floating in space like a cartoon bubble, except they are long and skinny. Incidentally, the same thing happens within natural clouds, but it doesn’t take a jet engine to make a cloud.

All of this depends not only on the temperature, but on how much moisture is in the air. If the air is too warm, there is no contrail, or it evaporates very quickly. If there is not much water, the contrail evaporates more quickly. If there is a lot of moisture in the air, the contrail hangs around longer.

The wind can also play a role, as it blows the ice crystals apart, hastening diffusion. Of course, the wind at high elevations may be very different than what we experience here on the ground. I’ve heard it said that there is more wind up there than there is down here, even in this column. In fact, many contrails spread out and create a high, thin, cloud cover that has been shown to effectively cool the earth. When all flights were grounded for a week after Sept. 11, the earth warmed noticeably. Now THAT was man-made global warming.

So, no, you can’t tell by its width how long ago a contrail formed because there are too many variables. But I can tell you that, if you watch contrails instead of the highway, you will go where you aren’t.

Gary McCallister, .(JavaScript must be enabled to view this email address), is a professor emeritus of biological sciences at Colorado Mesa University.

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