Why is it more Humid at Night?

Alex Williams
11 Min Read

Global warming is increasing the temperature considerably and our Earth is becoming hotter with every passing year. Humidity is also a part of the climate cycle. Did you know that the first instrument known to mankind for measuring the humidity of air or gas was built by Leonardo da Vinci in the 1400s and he named it hygrometer? By the way, have you ever wondered why is it more humid at night and what time of the day is humidity highest? If not, let’s find it out.

1. What is Humidity?

After evaporation, the concentration of water vapor in the air is known as humidity. It is the indicator of the dew, fog, or precipitation which are present in the atmosphere. The relative humidity is the measurement of the amount of water in the air in relation to the maximum water vapor in the air. The hot air can hold more water vapor, raising the humidity levels. 

2. How does Humidity form?

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Before understanding why is it more humid at night, let’s go through its process of formation. When the water gets evaporated due to overheating on the surface of the Earth, it rises and disperses into the air, and the droplets attach themselves to the particles in the air. These invisible water droplets are known as water vapor. When water vapor combines with air in the atmosphere, it makes the air humid. Humidity is not just outside but inside your houses too. Must read how is dew formed?

3. Why is It more Humid at Night?

During the night, the air temperature drops in consideration of the drop in temperature of its surroundings. Since cold air cannot hold much water vapor or moisture because it has a low saturation point and the vapor exceeds the holding capacity, it condenses on the ground in the form of dew drops. Therefore, both cold air and temperature cause more humidity at night. (See How does Radiation Fog develops in the Valley at Night?)

4. What Time of the Day is Humidity Highest?

After clearing your curiosity about why is it more humid at night, let’s see at what time of the day is humidity highest. In the early morning hours, the temperature is not as high as it is during noon. Therefore, the air is relatively cool and it has kept the moisture in the lower layers of the atmosphere. The relative humidity is highest during midnight and early in the morning because of the higher amounts of water vapor or moisture floating in the air. (See 12 facts about fog breath)

5. Does Every Place have the same Humidity Levels?

No, every place is distinguished by its latitudes and longitudes along with the movement of air. Therefore, the global distribution of humidity is different because of the presence of latitudes. (See What State has the Highest Humidity?)

Hot temperatures cause the evaporated water to rise at higher altitudes with the help of warm air and its high capacity to hold moisture. Therefore, when the temperature is high there is relatively less humidity. But lower temperature means less warm air which cannot take moisture to higher altitudes and as a result, it remains in the lower layers. It makes the air moist and humid. (See What is the Temperature of Water at Room Temperature?)

7. What causes a Rise in Humidity?

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Global warming is the major cause leading to a rise in the humidity levels too. The increasing temperature of the surface of the Earth makes the air warm as it passes over it. The increased solar radiation is causing more evaporation from the surface of the water bodies. Since the warm air has a high saturation point and can hold more water vapor it is causing an increase in the humidity levels. (See How elevation affects climate?)

8. What is the Accurate Level of Humidity?

Humidity is comfortable when it is in the range of 30% to 50%. It means there is only 30% to 50% water vapor in the air. It is not just the outdoor humidity level but even the indoors, if the humidity levels are more than this, it can cause discomfort. (See What is a Cold Front?)

9. Why is more Humidity Discomforting?

According to the National Centers for Environmental Information, a rise of about 0.55° Celsius (1° Fahrenheit) is capable of raising the humidity levels by 4%. This is probably the reason why increased humidity levels feel discomfort in summers more than in winters. The reason why is it more humid at night is applicable in winter too, but it is not problematic at that time of the year.

Another factor for discomfort is the non-evaporation of sweat on a humid day. The moist air is holding enough moisture that it does not let the sweat evaporate. This makes our skin sticky and we feel discomfort. It is also the reason why you feel hotter on humid days. (See What is Air we breathe made up of?)

10. What increases Indoor Humidity Levels?

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The root cause can be the outdoor humidity levels, but some indoor factors can be checked for the same. Take a look.

  • Laundry: Drying the laundry indoors is the major cause of the raised indoor humidity levels. Try to dry it outdoors and if not possible, dry it on a balcony. It is always better to dry these clothes in a dryer.
  • Indoor Plants: Having an indoor garden is bliss but not always because during summer these plants release a fair amount of water in the form of transpiration. This increases the moisture content in indoor air, making it more humid.
  • Poor Ventilation: Closed windows and curtains keep all that air inside your house. It is time to open those windows and let the house breathe. Especially, during the early morning hours because it’s when the humidity is highest in the day and that’s why the circulation of air becomes necessary.

11. How to Control Humidity at Night?

After knowing the reason why is it more humid at night you are finally here to know the ways to control humidity at night. The average indoor humidity should be around 30% to 50% and if it is more than that you should follow these methods to bring the humidity levels down.

  • Take Cool Showers: It does not mean you have to take a bath with ice water. But instead of a warm shower, just use water at normal room temperature. This will neither increase the body temperature nor will it increase the temperature of the surrounding air.
  • Use Exhaust and Ventilation Fans: It is necessary to use ventilation fans or exhausts while you cook. Because it will reduce the air temperature thus decreasing its saturation point. It is a useful method to reduce indoor humidity.
  • Use Air Conditioners: You must be using them already but using them during the night will help in reducing excess humidity levels at night. The cold air from the air conditioner will replace the humid and warm air. Make sure to clean the filters occasionally and change them when required. If your filters are dirty or old, this can be one of the reasons why is it more humid at night indoors even after using the air conditioner. 
  • Use Dehumidifiers: A dehumidifier works like a vacuum cleaner that takes in the warm air from one end, removes moisture from it, and blows out the dry air from another end. The moisture from the air is dripped inside a collection tank in the dehumidifier, and you have to empty it occasionally to keep the machine working accurately.
  • Use Charcoal Briquettes: A briquette is a compressed block of charcoal dust. Charcoal is known as a good moisture absorber; therefore, you can try this. All you have to do is to place one or two charcoal briquettes in an open basket or an open can and leave it. The block will absorb moisture and will work fine for a couple of months, after which you will have to change it.

So, the answer to why is it more humid at night is the low saturation level of air due to which it cannot hold much moisture. I hope this article answered all your questions! Also, check out Why is it Hotter in Summer?

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