All You Need To Know About Dew Point And How It Differs From Humidity

Water on a green leaf

Pour cold water into a glass on a hot day or check the cold water pipes in your shower, and you’ll see it. The water droplets form on surfaces – even when there is no leak.

So, where does this water come from?

The science behind this process is in two words: dew point.

This article aims to explain the dew point phenomenon, its measurement, the benefits of monitoring its levels, and how it differs from humidity.

What is Dew Point?

The dew point is the temperature at which water vapor in the air condenses into a liquid at the same rate liquid water vaporizes. In this state of equilibrium, the air's barometric pressure and moisture content volume remain constant.

When the air temperature drops below the dew point temperature, the aerosol water droplets condense into their liquid form which is called dew.

So, when the air around a glass of cold water comes into contact with the glass, the air cools down, and dew forms on the other side of the glass surface.

What is Humidity?

Humidity is the concentration of moisture content in the air at a given temperature and atmospheric pressure.

Relative humidity is the ratio of the number of water vapors in a given volume of air to the maximum amount of water vapors the same volume of air can hold. Generally, it is measured in percentage and is closely related to the dew point temperature.

How to Measure Dew Point Temperature

To measure the dew point, scientists use an instrument known as a hygrometer. It has a glazed mirror that cools down when air passes over it. Humidity sensors, like PurpleAir's air quality monitors, also use hygrometers to measure the dew point temperature in the atmosphere.

Here’s how you can use air quality monitors to measure the dew point temperature reliably:

  1. Evaluate if the sensor's measuring range meets your needs.
  2. The pressure range of the sensor determines whether it is possible to meet your needs or not. If you intend to measure the dew point of compressed air, you may need to expand it to atmospheric pressure and correct the reading.
  3. Install the sensor according to the manufacturer’s instructions. There should be unrestricted airflow around the sensor for an accurate reading. Avoid installing it in a dead-end pipe or a stub.

Differences Between Dew Point And Humidity

Although closely linked, dew point and humidity are different phenomena. Relative Humidity (RH) of 100% can be achieved by cooling the air to its dew point at a constant temperature. However, the value of the dew point depends on humidity. When the air is more humid, the air’s water content will condense at a higher temperature.

Another way to tell the two apart is in how they are measured. The dew point is an absolute measurement while humidity is a percentage. Hence, the dew point is considered a more accurate way of measuring the moisture content and comfort of the air.

Additionally, humidity is dependent on the temperature of the air while dew point is not. It is only possible to alter the humidity of a room by changing its temperature. When the dew point is the ideal control parameter, it is easier to control the environment's temperature and conserve energy.

3 Benefits Of Monitoring Dew Point

Today, the dew point is a standard parameter in environmental sciences and meteorology. Monitoring it during industrial processes such as metallurgy, semiconductor manufacturing, and natural gas processing in refineries is also critical.

Measuring and monitoring the dew point has 3 key advantages:

  1. Avoid corrosion, leaks, blockage, and even explosion in pipes due to excessive moisture.
  2. Avoid unwanted chemical reactions or contamination of final products with moisture.
  3. Conserve energy by monitoring dryer performance using heat for dehumidifying.

When studying the atmosphere, humidity and dew point are vital parameters to note. 

Worried About Air Quality?

Monitor the Particulate Matter levels around the world with our free, real-time PurpleAir Map. or join PurpleAir's mission to make air quality data accessible to everyone by investing in an air quality monitor for your home. 

Together, we can be informed and make changes in our daily habits and the community to improve air quality.