7 things you didn’t know about humidity

1. Humidity 100%,

does not mean it will rain

Humidity is a physical quantity used to describe the content of water vapor in the air. There are many ways to express the level of air humidity, the most commonly used of which is "relative humidity" in meteorology.

So what is relative humidity? Let's think of air as a sponge that can hold up to a certain amount of water, say 1 liter. Then relative humidity refers to the ratio of the actual water content of the sponge (i.e. absolute humidity) and the maximum amount of water it can hold. If the sponge drinks no water, the relative humidity is zero; if the sponge drinks 500 ml of water, the relative humidity is 50%.

The maximum amount of water vapor the atmosphere can hold depends primarily on temperature. A rise in temperature is equivalent to making a sponge bigger, able to hold more water. So, when you increase the size of the sponge without adding more water, the relative humidity decreases.

If you continue to add water after the sponge is full of water, the excess water vapor will precipitate out. But this doesn't mean it will definitely rain. Because relative humidity is usually measured at ground level, it does not accurately reflect humidity aloft.

Even when the humidity at high altitude reaches saturation and the excess water vapor condenses into small water droplets, these precipitated small water droplets will not immediately fall into rain like in a water-saturated sponge. Because they are light and small (mostly only 0.01~0.02 mm in diameter), they are held up by the rising air and form floating clouds. Only when the small water droplets continue to absorb water and grow so fat that the air cannot hold them, will they drip and turn into drizzle.

So, 100% humidity does not mean it will definitely rain.

2. The higher the dew point, the more uncomfortable it will be for people

However, when the humidity reaches 100%, dew will definitely appear.

When the water vapor content remains unchanged, the temperature decreases, which is equivalent to the sponge becoming smaller, and finally the water vapor in the air reaches a saturated state. As a result, excess water vapor precipitates out and turns into dew.

The ambient temperature when water vapor in the air condenses to form dew is called the dew point. For example, the dew point is 18°C, which means that the outside temperature must drop below 18°C ??before the water vapor in the air reaches saturation, forming small, sparkling water droplets on the grass and leaves.

Dew point is a measure of absolute humidity. For example, the dew point of a certain place is 12°C, then the absolute humidity of the air here is the saturated water vapor amount at 12°C.

It can be seen that the higher the dew point, the more water vapor in the air. When there is a lot of water vapor, the temperature or relative humidity is generally higher. After all, the larger the sponge, the more water it can hold, and the fuller the sponge is, the more water it can hold. On the contrary, the lower the dew point, the less water vapor in the air. There are two situations of low water vapor. One is low temperature, which means that the sponge is small and has little ability to hold water; the other is low relative humidity, which means that although the sponge is large, it drinks less water.

Although the weather forecast does not mention dew point, it is actually an important indicator of whether the body feels comfortable. Together with wind, sunlight and other factors, it affects our somatosensory temperature (that is, the air temperature that the human body actually feels).

People often feel uncomfortable when the dew point is high. Because as mentioned before, temperatures are generally higher at high dew points, which can make people sweat profusely. High dew points are sometimes accompanied by high relative humidity, which blocks the evaporation of sweat and makes people uncomfortable or even sick due to excessive body temperature. When the dew point is low, the temperature or relative humidity will be relatively low, both of which can allow the body to dissipate heat effectively, making it more comfortable.

Water vapor in the air mainly comes from the evaporation of oceans and lakes. The higher the water temperature, the faster the water evaporates and the more water vapor is in the air. Therefore, most of the high dew point areas on the earth are close to warm waters, such as the Persian Gulf, the Red Sea and the Gulf of Aden, which are the three highest dew points in the world. area.

The Persian Gulf is the area with the highest water temperature on earth, and its water temperature in summer can reach 30~33℃. Therefore, the highest dew point ever recorded in the world - 35℃ (3:00 pm on July 8, 2003) occurred in Dhahran on the west coast of the Persian Gulf.

3. Cities are stinkier in summer

Have you ever noticed that cities are stinkier in summer, with bursts of stench floating in the air from time to time? Why is this?

In addition to summer garbage being more susceptible to decay, scientists have also found that people's sense of smell is more sensitive in humid environments. This is because high temperatures and high humidity cause more water molecules to float in the air and move faster. A large number of active water molecules carry more smelly particles into our noses, so cities in summer are stinkier.

This may also explain why a wet "soaked dog" smells worse. Dog hair is home to many microorganisms such as bacteria and yeast, which produce some unpleasant-smelling compounds. After the dog gets wet, these smelly substances will be carried into our noses by evaporated water molecules, making the dog smell worse.

The stench emitted by garbage can also be smelled in winter, but the cold, dry air will limit the distance the odor particles can travel, greatly reducing their lethality.

4. If the air is dry, it is easy to sing out of tune

Our vocal cords are composed of a pair of symmetrical mucous membranes.

When making sounds, the airflow from the trachea and lungs continuously impacts the vocal cords, causing the vocal cords to vibrate and produce sounds. The vocal cords control airflow to control the tone of our voices when we speak or sing. Interestingly, in a dry environment, it is difficult to sing without going off-key.

In fact, researchers speculate that it is humidity that gives language its rich tones. After counting more than 3,700 languages ??spoken around the world, they found that languages ??with complex tones - such as Cantonese, Vietnamese and many African languages ??- are more likely to appear in humid areas of the planet.

Research shows that the vast majority of languages ??with complex tones appear in tropical areas of Southeast Asia and Africa, with a small number located in humid areas of North America, the Amazon Basin, and New Guinea. Non-polyphonic languages, such as various European languages ??including English, tend to be found in drier places - the cold north or dry deserts.

The reason for this interesting pattern is that the humidity of the air affects the elasticity of the vocal cords. There is a fixed ratio of water and polysaccharides in the mucus layer on the surface of the vocal cords to keep the mucus layer soft and elastic, which is the key to sound production. Inhaling dry air will dehydrate the vocal cords, causing the mucus layer to become more viscous and less elastic, making it difficult to produce complex tones.

5. Hair can measure humidity

If you have long hair, you may not need to bother with the weather forecast to tell you the humidity of the air. Because hair is very sensitive to humidity, straight hair will become curlier and curly hair will become curlier when the air is humid. Swiss physicist Sausser also discovered this interesting phenomenon, and then he used hair to create the world's first hair hygrometer.

Sausle fixed one end of a 25.4-centimeter-long bundle of hair to a screw, and the other end passed through a pulley and was connected to a heavy object. The hair will become shorter after it absorbs water and becomes wet, driving the weight upward. Sausser calculated the humidity of the air based on the distance the weight moved.

Why does hair become shorter after absorbing water?

The main component of hair is a protein called keratin. We all know that proteins are composed of amino acids, which are arranged "hand in hand" into long peptide chains. As shown in the figure above, through disulfide bonds or hydrogen bonds, the peptide chain can form a helical structure and further fold.

The disulfide bond is very stable and is not affected by humidity. As long as you don't perm your hair, it can exist almost permanently. This gives our hair strength and resilience. The hydrogen bond is relatively weak, it is very sensitive to humidity and can be interrupted and reconstructed at any time.

When it is humid, there are more water molecules in the air, which means that in addition to hydrogen bonds can be formed between adjacent amino acids, there are also hydrogen bonds between amino acids located at different positions in the peptide chain and in different peptide chains. More hydrogen bonds will be formed, which will cause the peptide chain to continue to fold and bend. When the humidity decreases, many hydrogen bonds will be broken, and the peptide chain will stretch again and become longer. The macroscopic manifestation is that the hair becomes shorter as the humidity increases.

If you imagine hair as a spring, then blow-drying your hair is equivalent to straightening the spring, and the hair will become longer; when it is wet, the large number of hydrogen bonds formed will further bend and fold the spring. , or even tangled, and the hair becomes shorter.

Although hair hygrometers are very crude and you can even make them at home, it was not until the 1960s that hair hygrometers withdrew from the stage of history and were replaced by electronic hygrometers.

6. It is dangerous to exercise when it is hot and humid

Even professional athletes must adjust their exercises according to changes in humidity.

Baseball is a sport that is very affected by humidity. If the player cannot adjust the batting intensity according to the field, then for every 20% increase in relative humidity, a home run will occur (after the batter hits the ball, he successfully circles the base and returns to home plate before the ball is caught by the opponent player). Home run. The most direct way is to hit the ball directly outside the home run wall 90 to 100 meters away, so the probability of hitting the ball as far as possible will be reduced by about 25%.

When the humidity of the stadium is high, the baseball will absorb water and gain weight, causing the batting speed to decrease; the resistance of the ball in the humid air will also be greater. Under the simultaneous influence of the two, the baseball will fly The distance out will be shorter. For every 1 meter the ball travels less, the probability of hitting a home run decreases by about 7.5%. So, it's easier for players to hit home runs at higher altitudes because the humidity is lower and the ball travels farther.

In fact, strenuous exercise in a high-humidity environment is very dangerous. Because when we exercise in hot environments, our bodies cool down by sweating. If the air is dry, sweat can evaporate quickly and take away heat from the body surface, effectively lowering body temperature. But if the humidity of the environment is high, it is difficult for sweat to evaporate, and the body has to sweat more to try to lower the body temperature. Excessive sweating can cause dehydration, and if not treated in time, people can easily suffer from heat stroke.

So when it is hot and humid, it is best for everyone to reduce the time for outdoor exercise, and to replenish water in time after exercise.

7. Humidity tells moths where there is more nectar

The hot and humid environment that we hate is like paradise for insects.

Small bugs are more susceptible to dehydration than larger animals because their relative surface area (the ratio of body surface area to volume) is greater, which means they lose more water through transpiration from their body surface. .

And we know that most insects are very small, and high humidity will increase their survival rate, so most insects are very sensitive to humidity and always like a moist paradise. Among them, moths are the best, which can detect humidity changes as small as 4%.

In addition, moths can also find their food, nectar, by detecting changes in humidity.

Nectar has a transpiration effect, and the relative humidity above the heads of newly bloomed flowers will be about 4% higher than the environment. The humidity difference then gradually decreases until the nectar is exhausted after about half an hour. In other words, half an hour later, the flowers may still be blooming, but the nectar is gone. Moths can only enjoy nectar if they find flowers that are open for less than half an hour. Therefore, the keen perception of humidity changes can help moths quickly determine which flowers have more nectar.

This article is derived from an article in the 2016 issue of the magazine Big Technology* Science Mystery. Readers are welcome to follow our WeChat ID of Big Technology: hdkj1997