How Does Humidity Affect Weather, Health, and Daily Life?
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 in Physics: Definition, Types & Importance
1. What is humidity in physics and why is it important?
In physics, humidity is defined as the concentration of water vapor present in the air. It is a crucial atmospheric variable for several reasons: it plays a key role in weather patterns by influencing precipitation and fog formation, it directly affects human thermal comfort, and water vapor itself is a significant greenhouse gas that helps regulate Earth's temperature.
2. What are the main types of humidity explained with examples?
The three primary types of humidity are:
Absolute Humidity: This is the total mass of water vapor present in a given volume of air, usually expressed in grams per cubic meter (g/m³). For example, a reading of 15 g/m³ is an absolute measure of the water content.
Relative Humidity (RH): This is the ratio, expressed as a percentage, of the amount of water vapor in the air compared to the maximum amount it could hold at that specific temperature. For instance, 50% RH means the air is holding half the moisture it is capable of holding.
Specific Humidity: This is the ratio of the mass of water vapor to the total mass of the moist air parcel, expressed as grams per kilogram (g/kg). It is not affected by changes in temperature or pressure.
3. How is relative humidity different from absolute humidity?
The key difference lies in their dependence on temperature. Absolute humidity is a direct measurement of the water vapor in a volume of air (e.g., g/m³) and does not change with temperature. In contrast, relative humidity is a percentage that shows how saturated the air is. It is highly dependent on temperature; if the temperature drops, the air's capacity to hold water decreases, causing the relative humidity to rise even if the absolute humidity remains the same.
4. What is the dew point, and how does it relate to saturation?
The dew point is the temperature at which air must be cooled to become fully saturated with water vapor, reaching a relative humidity of 100%. When the air temperature reaches the dew point, it is at its saturation point. If the air cools further, the excess water vapor can no longer stay in its gaseous state and will condense into liquid water, forming dew, fog, or clouds.
5. How does temperature affect the relative humidity of the air?
Temperature and relative humidity have an inverse relationship. As temperature increases, the air's capacity to hold moisture also increases. Consequently, if the actual amount of water vapor (absolute humidity) stays constant, a rise in temperature will cause the relative humidity to decrease. Conversely, as air cools, its relative humidity increases, making it feel more humid even if no moisture is added.
6. Why do we feel more sweaty on a humid day than a dry day at the same temperature?
This happens because of the efficiency of evaporation, our body's primary cooling mechanism. On a dry day with low humidity, sweat evaporates quickly from the skin, which removes heat and cools us down. On a humid day, the air is already laden with water vapor, slowing down the rate of evaporation. Since sweat cannot evaporate efficiently, it remains on the skin, making us feel hotter and stickier.
7. How is humidity measured and what instruments are used?
Humidity is measured using an instrument called a hygrometer. The most common types are:
Psychrometer: This device uses two thermometers—a dry-bulb and a wet-bulb. The temperature difference between them is used to calculate the relative humidity.
Electronic Hygrometer: These modern devices use sensors that detect changes in electrical resistance or capacitance caused by atmospheric moisture to provide a direct digital reading of humidity.
8. Besides weather forecasting, where is the concept of humidity important?
Understanding and controlling humidity is crucial in many other fields. For example:
Manufacturing: To prevent corrosion and static discharge in electronics production.
Healthcare: To control airborne pathogens and ensure patient comfort in hospitals and incubators.
Agriculture: To maintain optimal growing conditions for plants in greenhouses.
Museums and Archives: To preserve delicate artifacts, documents, and artworks from degradation.
9. What is a common misconception about feeling humidity?
A common misconception is that relative humidity alone determines how "muggy" the air feels. However, a 60% relative humidity on a cold day feels very different from 60% on a hot day. The dew point is a more accurate indicator of human comfort because it measures the absolute amount of moisture in the air. A high dew point temperature always indicates high moisture content and will feel uncomfortable regardless of the relative humidity reading.
