What is Humidity?
Humidity is the amount of moisture or water vapour or water molecules present in the atmospheric gas. The more water in the vapour, the higher the humidity. Humidity arises from water evaporating from places like lakes and oceans. Warm water evaporates quickly. That’s why, you may find the most humid regions near to warm water bodies in places like the Red Sea, the Persian Gulf, and Miami.
Here, we will learn about the humidity and its types viz: specific, relative, and absolute humidity.
Types of Humidity
Relative humidity
Specific humidity
Absolute humidity
Relative Humidity
A meteorologist uses the term ‘relative humidity’. The relative humidity is a comparison of the amount of moisture present in the air to the amount of moisture air can hold. The amount of moisture the atmosphere can hold totally depends on the temperature.
The formula for the relative humidity is given by:
Relative Humidity = Actual amount of water in the air/saturated amount of moisture in the air can hold at that temperature
The relative humidity is the function of both water content (moisture) and the temperature.
Point to Remember
The relative humidity is 100% when the air is saturated with water vapour and 0% when no vapour is present in the atmosphere.
Relative Humidity Explained
Think of the atmosphere as a sponge and it is capable of absorbing a fixed amount of water, i.e., a mug of water. Now, think of a rise in temperature as an increase in the sponge size.
When the sponge has no water, it means the relative humidity is zero. Now, pour a half bucket of water on the sponge, the relative humidity reaches 50%.
We know that a sponge saturated with a half mug of water has 50% humidity, on increasing the size of the sponge (increasing the temperature) without adding water further, the relative humidity decreases because the sponge becomes bigger and is capable to take on water vapour; however, the amount of water remains the same.
Soaking a sponge (atmosphere) with water more than the capacity it can hold can lead to dripping; however, it doesn’t symbolize rainfall. So, how does rainfall occur?
Rainfall
Rainfall occurs when the rising air cannot hold enough water molecules that are gathered in the form of clouds in the sky.
Specific Humidity
We define specific humidity as the mass of water vapour present in a given unit mass of moist air.
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Specific humidity is equal to the ratio of water vapour mass and the air parcel’s total (including dry) air mass.
Specific humidity is also known as the humidity ratio. It does not change with the expansion or compression of an air parcel.
We usually express specific heat as grams of vapour per kg of air, or in air conditioning as grains per pound.
The specific humidity has great usage in meteorology.
Absolute Humidity
We define the absolute humidity in the two following sentences:
Absolute humidity is equal to the mass of water vapour per unit of volume of air, i.e., grams of water/cm3 of air. The formula for the absolute humidity is given by:
Absolute humidity = Mass of water/volume in cm3
Absolute humidity does not take temperature into consideration.
Absolute humidity in the atmosphere is between zero and approximately 30 gm/m3 when the air is saturated at 300C
Dew point is frequently cited as a more accurate way of evaluating the humidity and comfort of the air than relative humidity because it is an absolute measurement, unlike relative humidity.
When the dewpoint and temperature are the same, the relative humidity is 100 percent. Condensation will occur if the temperature falls lower, and liquid water will form.
If the relative humidity is 100 percent, which means the dew point temperature and absolute air temperature are both the same, precipitation is unlikely. It simply indicates that the maximum amount of moisture in the air is present at the current temperature. Fog on the surface and clouds in the sky, which are made up of microscopic water droplets suspended in the air, can develop from saturation.
While dew point provides a quick indication of air moisture content, relative humidity does not since humidity is proportional to air temperature. It can be put another way. One can calculate relative humidity based on the dew point. Also, the actual air temperature must be known in that case.
The actual saturation vapour pressure ratio is also known as relative humidity, where the real vapour pressure is a measurement of the amount of water vapour in a volume of air that rises with the amount of water vapour.
At any given temperature, saturated vapour pressure is the greatest Vapor Pressure that can exist.
Water vapour, whose VP is its SVP at the given temperature, exists in the air with relative humidity (RH) of 100 percent. This is equivalent to air in a state of equilibrium with liquid water. RH is the percentage representation of the VP/SVP ratio. 'dry' air will contain water vapour at the given temperature with a VP smaller than the SVP.
Effects of Humidity
Humidity can cause various uncomfortable conditions, let’s discuss these one-by-one:
Bacteria and viruses spread easily in humid conditions because of which people often fall sick, especially from respiratory issues.
When the relative humidity goes above 60%, the viruses spread among people, and they get ill.
The rise in the moisture content of air leads to the rise in temperature because of which the evaporation rate of sweat from our bodies slows. This slowdown leads to the following problems:
1. Overheating in our bodies
2. Exhausts easily, and
3. Consequences are lethal to health like Altered blood circulation, increased respiration rate, and sweating.
4. During humidity, higher levels of dust mites and fungi lead to allergies among people.
5. The spread of airborne chemical contaminants.
6. Detrimental to asthma sufferers.
What Method is Used to Determine Humidity?
A hygrometer is mainly used to measure relative humidity. The basic hygrometer is a sling psychrometer consisting of two thermometers connected by a chain and a handle. A single thermometer is standard. The other is a wet-bulb thermometer, a cotton wick over its bulb. The temperature of the air is measured with a dry bulb thermometer.
On the other hand, the wet-bulb thermometer has a moist cloth at the tip. As water molecules evaporate from the wet bulb's surface, they carry heat with them, decreasing the thermometer's reading. The vapour pressure, or the amount of water vapour in the air, determines the evaporation rate. No water will evaporate from the wet bulb at 100 percent relative humidity, and the readings on both thermometers will be the same. In a graph, comparing the two temperatures yields relative humidity results.
Fun Facts
In 1783, a person named Horace Bénédict de Saussure was the person to build the first hygrometer with hair. A hygrometer is a humidity measuring device.
Humidity provides us with a tonal language
Our vocal cords consist of a pair of mucus membranes that stretch across the larynx (our voice box). These membranes vibrate, controlling the air from the lungs that flow as we speak or sing. It means the level of moisture present in the air affects the elasticity of our vocal cords.
Singers can tell us how hard it is to carry a tune in a dry environment.
As per the latest research, we are better at detecting smells in a humid environment because, in heat and high humidity, there are more water molecules in the air to bind and carry odorous particles into our nostrils.
FAQs on Humidity
1. When does dew occur? What is the dew point temperature?
Dew occurs when the relative humidity reaches 100%.
We define a dew point temperature as an absolute measure of the amount of water vapour in the air. Dew point temperature is the best indicator of how comfortable or uncomfortable your day might go.
2. List some dew points with their conditions.
The below table lists the kind of a day with their respective dew points:
Dew Point | Kind of a Day | Dew Point | Kind of a Day |
40° | Perfectly summer day | 65° | An uncomfortable day |
50° | Comfortable day | 70° | Intolerable day |
60° | A little steamy day |
3. What is saturation?
When gas holds maximum water vapour at a given temperature, the capacity of the air to hold the moisture increases with the rise in temperature.
4. How humidity affects asthma sufferers?
Microorganisms like mould and fungi are known to cause respiratory issues like asthma. In a humid environment because of the easy spread of fungi in the atmosphere, even normal people experience hypersensitivity.
These microorganisms grow sharply when the relative humidity goes beyond 75% because of which it becomes detrimental to people suffering from asthma.
5. What is the dew point temperature?
The dew point is the temperature at which air must be chilled to achieve a relative humidity (RH) of 100 per cent at constant pressure. After that, the air can no longer hold water in the gaseous state. Water vapour would have to come out of the atmosphere in the liquid form if the air were to be cooled still further, which would typically happen as fog or precipitation. When the dew point increases, the amount of moisture also increases in the air.
6. What factors determine humidity levels?
The amount of moisture that can be included in the air increases as the temperature rises. As a result, even if the absolute humidity remains constant, the relative humidity fluctuates.
The relative humidity of a system falls as the system's total pressure lowers. Similarly, as a system's total pressure rises, the relative humidity rises until saturation is attained. If you want to learn more about these topics, download the Vedantu App. Experts have designed all the app and the website content to make it easily understandable to the students. You can even find free study content specifically designed for the competitive exams and the regular school syllabus of CBSE students.
7. Is it true that high humidity attracts bugs?
Excessive dampness in your home might attract a variety of pests. Springtails, camel crickets, and booklice are just a few insects that can be controlled simply by lowering the moisture or humidity in the home. Pests like cockroaches and ants can be attracted to excess wetness. Dehumidifiers function by removing moisture from the air, providing a dryer atmosphere in which creepy-crawlies have a more challenging time surviving. Although no bug is pleasant to see, those that seek moisture are the ones you want to avoid on your way to the bathroom.
8. What is the significance of humidity?
Humidity impacts human health because it influences our thermal comfort, or whether we feel hot or chilly. When the weather is hot and humid, the body struggles to stay cool because releasing heat through perspiration evaporation into the air is more complicated. One of the most important greenhouse gases is water vapour. We wouldn't survive on Earth if it weren't for water vapour. Water vapour acts as a greenhouse gas, allowing solar energy to pass through and warm the Earth. The Earth then radiates energy away, but some of it is trapped by greenhouse gases on its way out, adding extra warmth.
9. What are the negative consequences of using a dehumidifier?
A dehumidifier may or may not work for everyone. Uses of something else in your space may create some unintended consequences. Dehumidifiers help to dry out the air. A dehumidifier may not be essential if you live in a dry climate such as a desert or high-altitude area or heat your home with gas or electricity. When the air is arid, conditions like pneumonia might worsen.
