The “Dog Days” of summer are here, and in no time, the mercury can go from a comfortable 60° to a scorching 95°. Adding to the misery most of the time is the humidity. With a relative humidity of 50% when the temperature is 95°, it actually feels more like 105° outside. Whew…
The hottest days of summer in Wisconsin often involve higher humidity levels, making the air feel “heavier.” But did you know the air on a humid day is less dense compared more comfortable day with the same temperature? It may sound odd, even to me at times, but science proves this fact outright.
To answer this question, we have to dust off the old chemistry book. Now think back – for some of you waaayy back – to your high school or college Earth science class. In total, Earth’s atmosphere is composed of 78% nitrogen, 21% oxygen, and 1% other gases. It is estimated water vapor represents 0.40%, not a lot in the grand picture. However, when we experience a humid day, the amount of water vapor in our local atmosphere is much greater.
So why is the air less dense, or in layman’s terms, not as “heavy?” The water molecule, famously known as H2O, has significantly less mass compared to oxygen and nitrogen molecules, the gases that make up 99% of our total atmosphere. When more water vapor is present on a regional level, more oxygen and nitrogen is displaced to other areas. Think about this concept by imaging a ship and a sailboat. Both vessels float, but the ship’s large mass allows it to push away, or displace, more water compared to the dinky sailboat.
Now, I’m not about to go on air and tout or correct how humid air is actually less dense, other than for a learning moment when the weather is slow. I feel the humidity just like you do on the hot days, waiting for that next front to bring relief, and maybe a little rain too. Have a great day and thanks for reading my blog!
This post was written by Nick Grunseth on June 25, 2012