This lesson provides multiple texts to build on your understanding of humidity. You will use these texts to evaluate the rules about humidity you came up with during the lab, as well as expand your knowledge of humidity. 

Text 1: Have you ever visited a place that just made you feel hot and sticky the entire time, no matter what you did to cool off? You can thank humidity for that unpleasant feeling.

Humidity is the amount of water vapor in the air. If there is a lot of water vapor in the air, the humidity will be high. The higher the humidity, the wetter it feels outside. On the weather reports, humidity is usually explained as relative humidity. Relative humidity is the amount of water vapor actually in the air, expressed as a percentage of the maximum amount of water vapor the air can hold at the same temperature.

Think of the atmosphere as a sponge that can hold a fixed amount of water, let's say a gallon of water. If there is no water in the sponge, then the relative humidity would be zero. Saturate the sponge with half a gallon of water - half of what it is capable of holding - and that relative humidity climbs to 50 percent. When humidity is high, the air is so clogged with water vapor that there isn't room for much else.

If you sweat when its humid, it can be hard to cool off because your sweat can't evaporate into the air like it needs to.

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Text 2:
Now, a new global study projects that in coming decades the effects of high humidity in many areas will dramatically increase. At times, they may surpass humans’ ability to work or, in some cases, even survive. Health and economies would suffer, especially in regions where people work outside and have little access to air conditioning. Potentially affected regions include large swaths of the already muggy southeastern United States, the Amazon, western and central Africa, southern areas of the Mideast and Arabian peninsula, northern India and eastern China.
 

“The conditions we’re talking about basically never occur now—people in most places have never experienced them,” said lead author Ethan Coffel, a graduate student at Columbia University’s Lamont-Doherty Earth Observatory. “But they’re projected to occur close to the end of the century.” The study will appears this week in the journal Environmental Research Letters.

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Hot summertime temperatures in Chicago are often accompanied by high humidity, making it feel much warmer than it actually is. The saying – “it’s not the heat, it’s the humidity” – is often true during Chicago’s summer. The high humidity often results in oppressive heat index values and dangerous heat waves during the summer months. The heat index is an index that combines air temperature and relative humidity to measure the human-perceived equivalent temperature (i.e. how hot it actually feels).

Studies have projected that the region will experience higher dew points in the future, leading to hot days feeling even hotter due to this increased humidity. As a result of higher temperatures and humidity in Chicago, the frequency, duration, and intensity of heat waves are likely to increase substantially in the future. One study projects an increase of between 166 to 2,217 excess deaths per year from heat wave-related mortality in the City of Chicago by 2081- 2100, depending on the climate model.

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In 1783, Horace Bénédict de Saussure built the first hygrometer, a device to measure humidity, and he built it with… hair. To understand how it worked, you need to know a thing or two about hair.

A single strand of hair has many layers. The inner layer is filled with proteins called keratins that bind to each other, giving shape to your luscious locks. These proteins bind by forming tough disulfide bonds or weaker hydrogen bonds. You can thank hydrogen bonds for the funny way your hair dries naturally after getting out of the shower. Water molecules (two hydrogens and an oxygen) are soaked up by your hair and act as a bridge linking keratin molecules together in place. These hydrogen bonds keep your hair fixed in shape until you wet it again, allowing new hydrogen bonds to form.

In high humidity, water molecules in the air find their way into straight strands. As hydrogen bonds connect keratin proteins, hair starts to fold back on itself and curl. Frizzy fly always occur when hair folds back enough to break the cuticle – or the outer layer of hair that looks like dragon scales under a microscope.

Enter hygrometer. Saussure attached one end of a 10-inch piece of human hair to a screw. The rest of the strand he maneuvered through a pulley and attached to a weight. As the hair took on moisture, the strand curled and shortened moving the pulley and lifting the weight. Saussure could then calculate how much humidity was in the air based on how much the weight moved.

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Use the texts you've read to answer the following questions. Refer to multiple texts in your answers.