If you look out of the window, especially on autumn days, it can happen that you can hardly see anything at all. The reason: fog. It looks like we’re wrapped in a gray cloud.
What is fog?
Just like clouds, fog consists of many small water droplets. The biggest and only difference is that clouds are in the sky and fog is on the ground.
How is it made?
Fog can occur especially when the days are warm and the nights are cold and long. The warmth of the sun allows the water to evaporate during the day. Since it is colder again at night, the air cools down considerably. The previously evaporated water, which is in the air as water vapor, condenses. That means it will be liquid again. As a result, very small water droplets form in the air, which we then perceive as fog.
Some days the fog is thicker than others. It has to do with the temperature. The colder it is at night, the more the air cools down. Less water vapor fits into cold air and it makes it appear denser.
Throughout the morning the sun warms the air again. This causes the water droplets to evaporate again and become invisible to our eyes.
Dangerous or useful?
Fog can be very dangerous when driving a car. In heavy fog, the driver can sometimes not see the road and so it is easier to get off the road. For this reason, the rear fog light should be switched on in fog. Other obstacles can only be recognized later through the fog, when it is often too late to avoid safely. It is therefore particularly important not to drive too fast and to pay special attention.
But the fog is not always dangerous or harmful. Some countries also use the fog to obtain drinking water for the population. They use a grid with very small holes to filter the water out of the mist. Since the water droplets settle on the grid, large amounts of drinking water can be obtained, depending on the density of the fog.