Following Tuesday's column on weather misconceptions, a number of people asked how dry air can be heavier than humid air. The answer involves the chemical makeup of the molecules.
Water vapor is H2O, meaning each molecule has two hydrogen atoms and an oxygen atom. Each of the two hydrogen atoms has a molecular mass of one Dalton, for a total of two. Each oxygen atom has a molecular mass of 16 Daltons. Therefore, each molecule of water vapor has a molecular mass of 18 Daltons.
Meanwhile, ambient air is 78 percent nitrogen, which is N2 and has a molecular mass of 28 Daltons. Therefore, the higher percentage of water vapor there is in the air, the higher the percentage there is of lighter molecules. Even though hot and humid air makes us feel sluggish, it is, in fact, lighter air.
Have a weather question you'd like answered? E-mail weather@wday.com ,
or write to WDAY Stormtracker, WDAY-TV, Box 2466, Fargo, ND 58108
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