Fog vs. Smog

Difference Between Fog And Smog

Fog is a mass of clouds that forms at or touches the ground. Smog is a mixture of fog and other ingredients that is considered a form of air pollution.

How Fog Is Formed

You can get an idea of how fog forms if you understand what happens in your bathroom as you take a hot shower. As you take a shower, tiny droplets of water spray into the bathroom air. Since this air is dry initially, these droplets quickly evaporate, forming an invisible gas called water vapor. The longer the shower runs, the more water vapor enters the air. There is a limit, however, to how much water vapor the air can hold. When no more water vapor can enter the air, the air has reached its saturation temperature, also called its dew point. When this state is reached, the excess water vapor in the air condenses, or changes from a gas to a liquid. It condenses on cool surfaces such as mirrors and windows. It can also condense on dust, pollen, and other small particles in the air, forming a cloud of fog in your bathroom.

When the air in your bathroom becomes warmer, you will see the fog “clearing.” In just a few minutes, the millions of tiny water droplets evaporate, changing back to the invisible gas, water vapor. This occurs because warmer air can hold more water vapor than colder air. This is what happens outdoors in the morning after a foggy night. As the morning sun warms the ground and the air, the fog “burns off”—the liquid droplets evaporate and become a gas.


There are two kinds of smog. One includes excessive concentrations of smoke from burning substances. The other sort is brought on by a chemical reaction that occurs when substances within the air are in contact with sunlight. Each sorts of smog usually develop throughout a situation known as a temperature inversion. This happens when a layer of cool air near the bottom is trapped by a layer of heat air above it, and winds are too light to move the layers of air. This condition prevents air from mixing vertically and retains the smog concentrated near the ground.

Something that pollutes the air can contribute to smog. This consists of gases that are produced by coal burning, wooden, gasoline, and different fuels and even pure gases and substances that happen in nature.

Smog has occurred throughout history. For example, in America’s early colonial period, the term “Indian summer” was often used to describe the time after the first frost when smoke from fires hung in the air. During the late 1800’s, smog was a serious problem in London and other large cities as a result of the extensive burning of fuels such as wood and coal.


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