Dew is an atmospheric condition where water condenses in the form of water droplets on an exposed object in the morning or evening. It can be seen as lustrous drops on the surface of leaves, grass, and other objects during wintertime. Fog, on the contrary, is a bulky cloud encapsulating water droplets or ice crystals suspended in the air or close to the surface of the earth.
Dew vs Fog
The main difference between dew and fog is that dew is formed from the water droplets that lead to the condensation on colder objects. In contrast to that, fog is formed due to light winds that remain on the earth’s surface.
Dew is defined as the moisture that is formed at night when the heat on the outside cools down. Dew is mostly formed on metal surfaces. Moreover, dew can be formed in any season, especially when nights are calm.
Fog is the low-lying cloud of water droplets that are present at low heights. Moreover, it is a cloud that can touch the ground. Fog is different from the mist. Fog is much denser than mist. There are different types of fog that include radiation fog, advection fog, etc.
Comparison Table Between Dew and Fog
| Parameters of Comparison | Dew | Fog |
| Definition | Water vapor in hot air condenses to make shiny droplets on cold surfaces | A type of aerosol in the form of a cloud formed near the surface of the earth |
| Formation | Calm wind containing water droplets condenses on colder objects | Little water droplets are formed, and due to light, winds remain hanging near the earth’s surface |
| Occurrence | Generally formed on metal surfaces, leaves and grasses, railings, car roofs, and bridges. | It never settles on surfaces, always present as a low-lying cloud |
| Characteristic | When the temperature lowers further, the water droplets change into ice, and this form is called Frost. | It is closely related to mist. It is considered a denser form of mist. |
| Measured by | It is measured by a device called a drosometer. | It is measured in terms of visibility, i.e., the amount of light transmitted from a light source 50 meters away. |
What is Dew?
Dew is the natural form of water that is formed when water condenses. The dew is the result of water changing from the stage of vapor to another liquid stage. This process is known as condensation, where any material undergoes change from gas to liquid. The formation of dew occurs when the temperature drops and the objects cool down. When the object cools down, the air that is surrounded by the object also cools down. This cool air surrounded by the object will be less able to hold the water vapors as compared to warm air. This is how the process of condensation takes place and leads to the formation of small droplets called dew.
The temperature at which the dew is formed is called the dew point. This dew point varies depending on the location and various other parameters such as weather, any time of day, etc. The formation of dew mostly occurs at night because of the temperature drop. If the warm and humid temperature condition is there, then the dew would form in heavy amounts, and the people collect this dew as a water source. The instrument that is used to measure dew is called a drosometer.
What is Fog?
The fog is a type of cloud that touches the ground. It can be thick as well as thin also. In winters, people face difficulty in seeing through the fog. The process of the formation of fog occurs when the water vapor in the gaseous form condenses.
During the process of condensation, the water molecules combine and make tiny droplets of water that are present in the air. The fog happens to be very humid because there are a lot of water vapors in the air that form fog. Few types of fog exist in nature, and that includes ice fog, radiation, etc.
During the summer season, the ground absorbs the earth’s surface absorbs the radiation from the sun and air and becomes warm and moist, and when the season changes, this warm air combines with cooler air and condenses quickly to form the fog. Another condition is when fog is formed when the humidity reaches its maximum level that is up to a hundred percent, these small droplets get converted to large droplets. The fog can be measured through various types of methods such as transmission method, forward scatter, backscatter, etc.
Main Differences Between Dew and Fog
- Dew can form in any season when nights are calm and clear, whereas fog generally forms during change of season.
- Dew is formed on surfaces like railings. Bridges and other metal objects while the fog is formed like a cloud near the surface of the earth.
- Dew disappears as the sun shines or temperature rises, whereas fog may remain throughout the day.
- When the temperature drops further, the dewdrops change into ice flakes and are termed frost, whereas fog is formed after mist. Fog is denser than mist.
- Dewdrops are not harmful to humans, whereas fog causes respiratory problems, irritation in the eyes, and many other health hazards. It also impacts the visibility in the air.
Conclusion
The dew and fog are two different phenomena of the atmosphere that are based on evaporation and condensation. There are major factors that affect the formation of both dew and fog, such as altitude, wind speed, temperature, and water bodies. Dew is formed when water condenses, whereas fog is a type of cloud that appears close to the surface of the earth. The fog forms when the water droplets become bigger due to the low temperature, whereas dew is formed when temperature drops and objects cool down. Both the phenomenon is common in cold seasons. But Fog forms at night and is visible mostly in the morning, whereas dew also occurs at night and is visible on leaves, grass, and twigs.
References
- https://onlinelibrary.wiley.com/doi/abs/10.1002/jpln.200625002
- https://www.sciencedirect.com/science/article/pii/S0367253010001015