Have you ever been in such cold weather that you could see your breath? Did you feel as though you were a mythical creature emitting a cloud of mist each time you breathed out? Well, sorry to ruin your fantasy, but there’s a scientific explanation for this fascinating phenomenon.
As you probably already know, every time you inhale, your lungs absorb oxygen from the air. When you exhale, your lungs put carbon dioxide (CO2) back into the air. The warm air released from your body with each exhalation contains vapor because of the moisture from your lungs, throat and mouth. The warmth gives the particles of water the energy they need to keep moving rapidly. But when the air outside is cold, the water particles slow down and move closer together, forming little drops of water in the air, which is a process referred to as condensation. These drops of water suspended in the air appear like a cloud under lights, which is why you are able to see them.
How cold does it need to be for you to witness this phenomenon? Actually, there’s no set answer. It depends on other factors, such as the humidity level of the air — the more humid the air, the more visible your breath will be. But generally speaking, you can usually see your breath when the temperature reaches around 7°C or cooler. One tip to see it more easily is to open your mouth wide and exhale from deeper in your throat so that the air coming out will be warmer and carry more vapor.
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So, the next time the mercury in the thermometer plummets, step outside, take a deep breath, exhale and enjoy the spectacle!
Photo courtesy of Shutterstock 照片：Shutterstock 提供
What Did You Learn?
1. Which of the following words in the passage means “the transformation of a gas into a liquid”?
(A) Spectacle. (B) Exhalation.
(C) Phenomenon. (D) Condensation.
2. Which of the following statements is true about the air exhaled from the human body?
(A) It stops moving if the temperature is too low.
(B) It contains a large amount of oxygen.
(C) It is a gas and normally not visible.
(D) It is completely dry and warm
3. According to the passage, under which circumstances will you be less likely to see your breath?
(A) Breathing out air on a freezing rainy day.
(B) Releasing your breath when the weather is chilly.
(C) Blowing out your breath when the temperature is below 0°C.
(D) Taking a deep breath under the sunlight and expelling it from the nose.
答案：1. (D) 2. (C) 3. (D)
Word in Use
1. emit vt. 發出∕排出（氣體、氣味、光等）
The hot steam emitted from the iron helps press the clothes.
2. absorb vt. 吸收
Mina used the mop to absorb the spilled milk before her mom got home.
3. vapor n. 水蒸氣
Clouds are formed when water vapor is turned into droplets.
4. particle n. 粒子；微粒
Airborne particles include ash, dust or pollen, and are invisible to the naked eye.
5. suspend vt. 懸浮，懸掛
The decorations were suspended from the ceiling by thin string.
1. as though + S + V 好像∕彷彿…
Tina acts as though she’s tough. In fact, she is quite timid.
2. be referred to as... 被稱為…
Taiwan was referred to as Formosa by Portuguese sailors.
3. generally speaking 一般來說
Generally speaking, the magazine is published monthly, but it sometimes publishes bimonthly.
4. take a deep breath 深呼吸
Before archers release an arrow, they take a deep breath to keep their hands steady.
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