What Is The Difference Between Fog And Smog?

Fog and smog are differentiated by their different causes and effects.
Fog and smog are differentiated by their different causes and effects.

The terms fog and smog are often used interchangeably even though they refer to two different phenomena. The term fog refers to a visible collection of water droplets suspended in the air. Fog can also be made up of crystals of ice suspended in mid-air. Several experts consider fog to be a variety of clouds found close to the earth's surface. On the other hand, the term smog refers to a type of air pollution that originated in the early 20th century. The term was created through the combination of the words smoke and fog. Before the coining of the term smog, the phenomenon was commonly referred to as pea soup fog. There are several fundamental differences between fog and smog such as the method of their formation as well as the effects they have on the environment.

Formation of Fog

One of the most significant differences between smog and fog is that they are formed in different ways. According to several experts, fog occurs due to the variation between the dew point and the air temperature. The term dew point refers to a specific temperature that air must be cooled to for it to be considered saturated with water. When the difference between the two temperatures is less than 36.5°F fog formation could result. At this temperature, the water vapor in the air condenses and forms minuscule droplets of water suspended in the air. The condensed droplets then gather together and form a visible cloud-like structure. Another factor that is vital for the formation of fog is that the relative humidity needs to be as near 100%. In some cases, fog can result even if the relative humidity is not close to 100%. On the other hand, meteorologists have proven that fog will not necessarily form even if the absolute humidity is 100%.

Formation of Smog

Smog, on the other hand, is rarely caused by naturally occurring factors but is primarily caused by human-made conditions. The use of coal has been known to result in the formation of smog. When coal is burnt to produce energy, a thick dark cloud of smoke is formed, and it interacts with the surrounding fog to create smog. In other areas, smog results from traffic emissions from vehicles such as buses and trucks. The primary natural cause for smog formation is the eruption of a volcano. However, for a volcanic eruption to cause smog, the emission needs to have two primary characteristics; the presence of sulfur dioxide in high quantities and vast amounts of particles. In the absence of these two conditions, natural smog cannot be formed. Experts often refer to this variety of smog as vog to identify that it has a natural cause instead of a human-made.

Types of Fog

Fog and smog are also different because there are several types of each phenomenon. There are several types of fog with some of the most common being radiation fog, evaporation fog, and advection fog. For fog to be considered radiation fog, it must have been formed after the sun had set and there should be a clear sky. In warmer months, radiation fog lasts for a very short time after the sun rises, however in the winter months, the fog can last longer. Evaporation fog on the other hand often occurs when cold air passes over a body of warmer water. In some cases, steam devils have been known to precede the evaporation fogs. On the other hand, advection fog occurs when an air mass containing water vapor passes over a surface that is relatively cooler than the air mass due to the action of wind. Advection fog commonly happens in snowy regions as a warm air mass is blown over the cold snow. Advection fog also happens in the sea when a warm air mass passes over cold sea water. The coast of California is one of the places where advection fog is most common.

Types of Smog

On the other hand, there are two main types of smog which are both named after the seasons, winter and summer smog. The two types of smog are mainly distinguished by the time when they are formed as well as the methods through which they are formed. Summer smog, as the name suggests, is mainly formed in the summer months. Due to the higher quantities of sunlight and the higher temperatures, more photochemical smog, which is classified as a type of summer smog, is formed than other types. In the winter months, due to the increased use of fossil fuels to heat buildings, the smoke contributes to the formation of winter smog.

Impacts of Fog

Fog and smog are also distinct because they have different impacts with fog primarily affecting people's visibility while smog has a major effect on people's health. The main impact of fog is that it results in reducing visibility. As a result of the reduced visibility, road accidents are common. Air travel is also greatly affected by the presence of fog.

Impacts of Smog

Scientific research suggests that smog affects the health of a large number of people. The people who are significantly affected by smog are the older member of society, the children, and those with chronic diseases that affect their lungs and hearts. It has been suggested that smog can reduce the amount of air that the lungs can hold. Smog has been shown to have a significant impact on the nose and eyes as it reduces the moisture content in their protective membranes. Research from the Ontario Medical Association indicated that close to 10,000 people die each year in the province of Ontario due to complications caused by smog. Research in California suggested that smog may also be responsible for some congenital disabilities.

Methods That Have Been Taken to Reduce Smog

Because smog has a generally negative impact on the environment, governments are putting in place several measures to reduce the quantity of smog in the atmosphere. The primary method to combat smog is by reducing the pollutants that contribute to its formation.


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