Humidity is a measurement of the amount of water vapor present in the atmosphere or a gas. 

Humidity is high when there is a lot of water vapor in the air. The higher the humidity, the wetter it feels outside.

The temperature and pressure of the environment being measured impact humidity. In cool air, a fixed amount of water vapor results in higher humidity than in warm air. 

Furthermore, as the temperature rises, the volume of water vapor necessary to reach saturation increases.

The figure above shows the psychrometric chart. A psychrometric chart is a tool for analyzing the correlations between various supply air properties and relative humidity.

Humidity is crucial to comprehend because it impacts both weather and climate and global climate change. 

Understanding how humidity affects indoor surroundings can help you decide where to store your books, clothing, and other vital objects in your home.

Ways to Measure Humidity

There are three specific methods to measure humidity. They are mentioned below:

1. Absolute Humidity

The water vapor concentration in the air, regardless of temperature, is absolute humidity. It is expressed in g/m3 (grams of moisture per cubic meter of air).

2. Relative Humidity

The water vapor content in the air compared to how much it can contain at that temperature is relative humidity. 

The percentage is used to express the value. Relative humidity of 50% means the air can hold half of the water vapor. 

In contrast, relative humidity of 100% indicates that the air is completely saturated with water vapor and can no longer exist. The more water vapor air can hold, the higher the temperature.

3. Specific Humidity

The mass of water vapor divided by wet air is known as specific humidity. It’s utilized for highly accurate calculations.

Importance

A steam humidifier in a room
A steam humidifier in a room | Image Credit – Aapsky

The term “humidity” has earned a bad rap for some reason. We usually relate with oily skin and a bad hair day.

But more importantly, finding the correct humidity balance in your home is critical for your comfort.  Whether you realize it or not, humidity levels significantly impact everyday life at your home. 

Humidity can harm your health and comfort irrespective of the place you live. Humidity can exacerbate the heat in the summer, making individuals feel exhausted, irritable,  and ill. 

While many people associate humidity with hot, heavy, and sticky outdoor air, indoor humidity levels are crucial. Climate control regulates the temperature and relative humidity in buildings, cars, and other enclosed places. 

It is necessary to ensure human comfort, health, and safety and meet the environmental requirements of machines, delicate materials such as artifacts, and technical operations.

The perfect humidity is not always easy to figure out, as it depends on personal tastes and outdoor temperatures. 

Home humidity should stay between 30 and 40 percent in winter in ideal conditions. In comparison, the summer allows a bit higher rate from 40 to 60 percent, although going into the upper limit of this range isn’t always easy. 

What exacerbates this problem is that you have to watch your humidity as outdoor temperatures change constantly.

By keeping your humidity levels between 40% and 60%, you can help minimize the spread of diseases by limiting the environment in which pollutants can flourish.

In addition, retaining desirable indoor humidity in your home, you can also help those suffering from sinusitis, bronchitis, and asthma. 

Because our airways are lined with fluids, slight dampness is excellent for our lungs and nasal cavities. 

When the air is dehydrated, our airways become inflamed and dry up; viruses might remain in the air when the air’s highly humid.

Below we discuss the effects and importance of humidity in different areas. 

1. Health

Low relative humidity can be unpleasant, as it dries the skin and mucosal membranes of the body. It also causes sore, itchy, cracked skin and a dry throat, nose, and eyes. 

It dries the mucous membrane, which is supposed to protect your respiratory system against catching pathogens.

Dry air can increase the frequency of bloody noses, raise your chance of contracting airborne viruses or infections, and cause respiratory disorders like asthma, bronchitis, and sinusitis.

Excessive relative humidity can induce discomfort, skin rashes due to sweat, irritation of the nose, eyes, and throat.

It may aggravate respiratory disorders, including asthma and allergy symptoms.

SNLow HumidityHigh Humidity
Itchy, dry skinMold and germs thrive in this environment.
Sinuses are irritatedExcessive sweating
Mouth and throat are dryNasal congestion 
Wooden furniture can crack and dry up over time.Wood furnishings might warp
Colds, flu, and other diseases are more common.Low energy and lethargy
The temperature in the house dropsThe temperature in the house rises
Humidity range for a healthy environment
Humidity range for a healthy environment – Sterling Chart| Image Credit – A V Arundel, E M Sterling, J H Biggin, and T D Sterling

The Sterling Chart depicts how relative humidity impacts human health and well-being. It demonstrates that humans’ ideal atmospheric humidity level is between 40 and 60 percent relative humidity. 

Biological pollutants and pathogens pose the least harm to human health in this ideal humidity zone. 

Colds, viruses, respiratory infections, dry eyes, itchy and chapped skin are common symptoms during the cold, dry winter months when the indoor RH is at its lowest.

2. Comfort

Humidity Indicator
Humidity Indicator | Image Credit – Aleksandr Kravtsov

Humans are more sensitive to temperature changes than to changes in relative humidity, despite humidity being an essential element for thermal comfort. 

Humidity has a minor impact on outdoor thermal comfort when low air temperatures. But a more significant effect when air temperatures are high.

Humans are sensitive to humid air because evaporative cooling is the principal method for temperature regulation in the human body. 

The pace at which perspiration evaporates on the skin is slower under moist settings than in arid conditions. 

We feel warmer if the relative humidity is higher than when it is low because humans detect the rate of heat transfer from the body rather than the temperature itself.

When relative humidity and temperature are too high, occupants are less able to dissipate heat through sweat, making them feel more uncomfortable. 

Depending on the temperature, humans can be comfortable within a wide range of humidities, from 30% to 70%. 

High relative humidity has also been linked to increased off-gassing of Volatile Organic Compounds (VOCs). 

These are harmful compounds generated by burning and off-gassing from several consumer products. This can cause discomfort to the people. 

A combination of high temperature and humidity may worsen scent problems and reduce odor acceptance. 

Even though the direct impact of humidity on scent is debatable, temperature and humidity do play a part in influencing one’s perception of odors. Low relative humidity can make inhabitants’ eyes, throats, and lungs uncomfortable. 

The humidity below and above the suggested levels can cause great discomfort to the occupants of that place.

3. Plant Growth

Thermometer and Hygrometer to measure optimal conditions for plant growth
Thermometer and Hygrometer to measure optimal conditions for plant growth | Image Credit – Evgen Prozhyrko

Photosynthesis requires a high level of moisture. When  plants lose too much water, the stomata close, causing photosynthesis to cease. 

If this occurs, the plant cannot absorb the required CO2, which is necessary to maintain photosynthesis.

Furthermore, a plant’s temperature is mainly controlled through evaporation cooling on a hot day. 

Evaporating water may remove a lot of heat from a plant and is an excellent technique to keep it cool. Open stomata allow a lot of air to pass through.

4. Keeping the stomata open

When there is more significant irradiation, it is vital to limit the plant’s evaporation to keep the stomata open. Evaporation decreases if the humidity in the greenhouse is kept high.

Furthermore, the temperature drops by adding humidity to the greenhouse, requiring the plant to cool less through evaporation. 

Finally, the crop can be wet slightly so that evaporating water can lower the yield or the greenhouse temperature.

It’s more crucial to keep the stomata open than getting the right amount of light. The stomata must be open to absorb CO2 and let photosynthesis occur.

Photosynthesis can happen with low light levels if the stomata are kept open. There will be no photosynthesis if the stomata are closed due to greater light levels. 

Of course, maximum photosynthesis is achieved by keeping the stomata open at the ideal light level.

The plant will stop growing if this process stops. The plant can keep its stomata open if the moisture in the greenhouse and around it is maintained at the proper level. The plant will absorb CO2, and the plant’s temperature will be controlled by evaporation.

5. Static Electricity and equipment failure

Equipment failure
Equipment failure | Image Credit – Weerapong Khodsom

Electro-static charges can accumulate in various types of IT equipment and individuals when the relative humidity is less than 40 percent

Static electricity is constantly generated in our environment by the friction of high-electric-resistance materials against one another. 

People walking on carpet is a good example. This energy becomes a problem only when the surrounding conditions enable it to collect, resulting in not only unpleasant symptoms such as when a person is discharged but also an explosive or combustible atmosphere, with the associated risk.

Furthermore, these phenomena are essential in computer laboratories and data processing centers. 

They can cause electronic circuit malfunctions, dust collection on readers’ heads, and even the breakage of stored magnetic media.

Increasing Relative Humidity (RH) does not stop these charges from developing, but it does prevent them from accumulating. 

Increases in R.H. form a fine layer of humidity on the surfaces of the materials. This allows the charges to go to earth before reaching significant levels of potential.

6. Deterioration of materials in a building

Damaged building materialc
Damaged building material | Image Credit – Sasin Paraksa

Buildings contain many metal elements, each playing a different role based on utilization. This application can range from a structural to a decorative role. 

High relative humidity can cause harm to your house or office. Mold, foggy windows, condensation, and warping of wooden furniture and window and door frames can all be caused by relative humidity levels above 70%

Loss of mechanical characteristics, warping, pitting, joint failures, and other materials failures are examples of typical failures induced by this type of degradation. This entails the replacement of the in-issue element and the associated cost.

When an electrical current passes from a higher potential area to a lower potential site, the metal corrodes. 

The reaction is accelerated when an electrolyte, such as a fine coating of water, is present.

7. Vehicles

Water vapor drops in car windshield
Water vapor drops in car windshield | Picture Source: Elena Kurkutova

It’s no mystery that warm and cold exterior conditions affect vehicles differently. There are difficulties to be concerned about during the harsh winter months, and there are also ones to be aware of during the summer. 

When your engine is running, it generates heat. When you combine it with even greater warmth in the atmosphere, the engine and cooling system is put under more strain.

High humidity within a vehicle can cause condensation issues such as windshield misting and electrical component shorting. 

These factors may be crucial to safety in automobiles, and pressure vessels like pressurized airliners, submersibles, spacecraft, and elaborate environmental control systems, including machinery to maintain pressure, are required.

Overheating the engine

If you drive your vehicle just too hard in the summer heat, overheating is always a risk. Always watch the temperature gauge and turn off the engine if it begins to overheat. 

If the overheating persists, you should have your car inspected by a professional. There could be damage to the machine or cooling system requiring professional assistance.

Air Temperatures: Hot vs. Cool

Hot air inherently contains more water than cool air, exacerbated by the summer humidity on the East Coast. 

Cooler air contains more oxygen. Your engine will work harder if more water and less oxygen is flowing through it. There may be a minor loss of performance and a decrease in fuel efficiency.

Problems with Air Conditioning

During the summer, you’re probably running your air conditioner a lot more. If you wish your air conditioner to perform at maximum efficiency, it may be time to tune up, recharge, and do vent cleaning. 

If your automobile starts to overheat, you should first switch off the air conditioning. You might even want to raise the thermostat/temperature setting. 

This will assist cool the engine by drawing some of the heat away from it. Roll down your windows to keep the interior of your vehicle from becoming too suffocating.

7. Aviation

Airplane
Airplane | Image Credit – Spooh

Airliners operate at a lower internal relative humidity, typically under 20%, primarily on extended flights. 

The low humidity is caused by bringing in very cold air with low absolute humidity, as observed at airplane cruising altitudes.

The relative humidity of this air decreases as it warms. Since the volume of water needed to be carried on board can be a significant weight penalty, humidifiers are not used to boost it to comfortable mid-range levels, causing discomfort such as painful eyes, dry skin, and drying out of mucosa. 

The ambient relative humidity can rise rapidly as airliners descend from higher altitudes into warmer air.  

Some of this moist air is drawn into the pressurized cabin and other non-pressurized areas of the airplane, condensing on the chilly plane skin.

On the interior and outside of the cabin, liquid water can generally be observed streaming over the aircraft’s skin. 

Components must be qualified to work in those settings due to the vehicle’s dramatic fluctuations in relative humidity. 

RTCA DO-160 specifies the recommended environmental standards for most commercial aircraft components.

Ice can form in cold, humid air, which is dangerous to airplanes because it alters the wing profile and adds weight. The risk of ice accumulating inside the carburetor is higher in carburetor engines. As a result, aviation weather reports include a relative humidity indicator, generally in the form of the dew point.

When determining takeoff distances, pilots must consider humidity because excessive humidity necessitates longer runways and reduces climb performance.

Density altitude refers to the height above standard atmospheric conditions at which the air density equals the reported air density at the observation site. 

In other words, the height is measured in terms of air density rather than the distance from the ground. 

The pressure altitude adapted for non-standard temperature is known as “Density Altitude.”

A rise in density altitude is caused by an increase in temperature and a lesser extent. As a result, the density altitude at a given site may be much greater than the actual altitude in hot and humid conditions.

8. Industry

Humidifier in an industrial operation
Humidifier in an industrial operation | Image Credit – Airtec

Humidity control is critical for various sectors to maintain high productivity. Maintaining ideal moisture levels is prevalent in industrial applications such as the food, pharmaceutical, electronics, printing, various manufacturing industries, and in a specialized market such as the upscale hotel industry. 

It is advantageous not just to the manufacturing process but also to the employees’ well-being and health. 

High humidity can wreak havoc on the capacity of chemical plants and refineries that rely on furnaces for certain operations (e.g., steam reforming, wet sulfuric acid processes). 

Flue gas fans must ingest air at a rate higher than would otherwise be required to maintain the same firing rate because humidity lowers ambient oxygen concentrations.

Dehumidification systems, such as compressor or desiccant dehumidifiers, will be required for some applications. 

Others, such as cold rooms for vegetables (over 90% RH at temperatures between 1 and 10°), will require a higher degree of humidity. The required humidity levels will vary depending on the indoor ambient temperatures.

In general, a relative humidity (RH) level of 40 to 60 percent is recommended for condensation avoidance and effective humidification benefits. However, every industrial application has its ideal humidity level for optimum production.

9. Humidity in partition walls and ceilings

Dampness at wet window
Dampness at wet window | Image Credit – Viktoriia Novokhatska

Air extractions can create negative pressure in humid areas. As a result, air would seep inside the building and settle in the spaces between partition walls and ceilings. 

If the temperature of the infiltrated air is lower than that of the surrounding air, such as behind a curtain or a sofa, saturation and even condensation may occur. 

This would give enough humidity for mold to grow, resulting in what is commonly referred to as “rising damp.”

10. Rainfall

Rainfall
Rainfall | Picture Source: Sassi Stock

The amount of water vapor concentration in the atmosphere also influences how much rain we get. 

Rainfall is proportional to the energy balance in the environment and the availability of tiny particles to form droplets around.

The amount of rainfall is determined by the water vapor concentration during heavy rain when all of the water in the air is frequently soaked out.

The higher the humidity, the more water vapor is produced, and the more rain is expected to fall. 

This is why tropical rain showers are more frequent and strong than those found in the United Kingdom.

As a result, humidity is a critical component of the weather, determining how heavy a heavy downpour is or how comforting it is.

11. Water Vapor

The water droplets formed after condensation
The water droplets formed after condensation| Image Credit – Akchamczuk

One of the essential greenhouse gasses is water vapor. Water vapor makes up more of the gaseous composition of the atmosphere than any other greenhouse gas.

Organisms on Earth wouldn’t be able to survive if it weren’t for water vapor. Water vapor acts as a greenhouse gas, allowing solar energy to pass through and heat the Earth. 

The Earth then transmits energy, but some of it is trapped by greenhouse gasses on its way out, adding extra warmth. 

The Earth’s average surface temperature is 14 degrees Celsius, but it would be roughly -18 degrees Celsius without greenhouse gases.

Conclusion

Raindrops
Raindrops | Image Credit – Urbazon

Humidity regulation is vital for material conservation and protecting human health. Material conservation refers to the permanent or temporary preservation of the features and attributes of the elements that comprise the structure. Corrosion is perhaps the most concerning issue in this regard.

As a result, strict relative humidity control can prevent material losses and the resulting cost loss. 

Even more crucial are factors affecting human health, such as the spread of fungi, insects, viruses, and bacteria. 

It’s vital to measure humidity conditions in places where rusting, condensation, mold, warping, or other damages to materials like metals, pharmaceuticals, and chemicals are likely to occur.

Humidity impacts comfort because the amount of moisture in the atmosphere affects how the body regulates its temperature. 

Too much moisture, for example, might make it difficult for the body to cool down, whereas too little humidity allows heat to depart the body fast.

Humans, animals, and plants are all affected by moisture. Humidity is among the determining elements for whether flora and fauna may survive in a given habitat.

However, demanding immediate attention, long-term climate control, and regulating temperature and humidity can be difficult due to day-to-day duties.

But ignoring such factors can result in respiratory problems such as allergies, asthma, or rhinitis.

Suraksha Pal is an Industrial Engineer currently pursuing my master’s degree in Renewable Energy Engineering at the Institute of Engineering, Pulchowk Campus. She has a keen interest in Renewable Energy and is passionate about sustainable development. She loves to express her views on these subjects through articles and blogs.