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Sunday, May 19, 2024

Ask Ms. Scientist: windchill and chopping onions

Dear Ms. Scientist,

How is the windchill index calculated?

Hana M.

Welcome to UW-Madison, where the only thing colder than the Humanities building is the air outside during this polar vortex we have recently entered. It sure is chilly out there on these first few walks to class this semester and the windchill temperature is a useful number to reference before you bundle up and head on out. The windchill number is only indicative of how cold your skin feels, not the temperature it is or ever will be. In actuality, your exposed skin can only reach 15 degrees Fahrenheit. Therefore, by using air temperature and wind speed, meteorologists are able to calculate a perceived windchill index that will give those outdoors an idea of how cold their skin will feel when exposed to the cold gusts. In fact, the National Weather Service uses just those two values and a prototypical human face tissue sample, in combination with the body’s rate of heat loss, to create a chart that will provide windchill temperature values.

Dear Ms. Scientist,

Why does chopping onions make me cry?

Lucy K.

So now you are back at school and cooking for yourself again—good for you! But, cooking for yourself means doing all the dirty prep work. Especially chopping those smelly onions! Onions contain an enzyme known as the lachrymatory-factor synthase, which is released into the air when the onion is cut. This enzyme then converts the onion’s amino acids sulfoxides into sulfenic acid. This sulfenic acid then becomes syn-propanethial-S-oxide, which, in the air, eventually irritates your eyes! Since it stings so much, your eyes produce more and more tears in attempt to wash away the gases. Some have their “tried and true” tricks to beat the waterworks when slicing and dicing that ultimately may or may not work. At the end of it all, you’ll hopefully have a delicious meal to share with an empty tissue box.

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Ask Ms. Scientist is wrtten by Julie Spitzer. If you have a burning science question you want her to answer, email it to

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