What Does Smog Mean?

The smog that is also referred to as smoke fog is intense air pollution and its name is derived in the 20th century from both fog and smoke as “smog” due to its nature of being opaque and for its typical odor. Smog is a mixture of nitrogen oxides, sulfur oxide, ozone, smoke, and other particulates. The kind of visible man-made pollution is derived from industrial emissions, coal combustion emissions, vehicle emissions, forest and agriculture fires along with photochemical reactions of these emissions.


Winter smog and summer smog are the two categories of smoke that are often discussed. Summer smog is often associated with the photochemical formation of ozone. In summertime photochemical smog is the dominant type of smoke that is formed because the temperature is warmer and there is more sunlight that is present. As the temperature is colder during the winter months and atmospheric inversion is common, the usage of coal and other fossil fuels becomes common to heat up houses and other commercial places.  Thus the winter smog formation is due to the excessive emissions due to the combustion of coal and other fossil fuels along with the lack of atmospheric pollutant dispersion under inversions.  


Both the primary and the secondary pollutants are the cause of the formation of smog. The primary pollutants are the pollutants that are emitted directly from the source like the emission of sulfur dioxide directly from the combustion of coal. The secondary pollutants such as ozone are formed when the primary pollutants after the emission from the source undergo a reaction in the atmosphere. 


Photochemical smog is a type of air pollution that is obtained from the admission that is generated from the combustion of the fuels in the engines and the industrial fumes. The pollutants give rise to secondary pollutants when they react in the atmosphere with sunlight and then combine with the primary emission to form photochemical smog. Since 2002 in cities like Delhi the smoke severity is aggravated by subtle burning in neighboring agricultural areas.


Most of this photochemical smog in many of the cities is increasing due to the inversion effect of the atmosphere that traps the pollution close to the ground. This topic, therefore, deals with what smog is, its types, cause, and effects.  


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Types of Smog

There are two types of smog as the cause behind the formation of smog is different. The two classifications of smog are as follows:-

  1. Photochemical Smog is also known as Los Angeles Smog: Photochemical smog definition is referred to as “summer smog” that is a type of air pollution developed from the admission that is generated from the combustion of the fuels in the engines and the industrial fumes.  Thus the photochemical smog formation happens with the chemical reaction of sunlight, nitrogen oxides, and volatile organic compounds in the atmosphere and leaves the air-born particles and ground-level ozone. It depends both on the primary pollutants and the secondary pollutants. Nitrogen oxides, particularly nitric oxide (NO) and nitrogen dioxide(\[NO_{2}\]), and volatile organic compounds are considered as the primary pollutants. Whereas,  peroxyacetyl nitrates (PAN), tropospheric ozone, and aldehydes are considered secondary pollutants. 

In the morning due to the high rush hours, a very high concentration of hydrocarbon and nitric oxide emissions mostly by the vehicles on the roads and also a small percentage due to the industrial emissions. Some of this volatile hydrocarbon rapidly oxidizes the OH group atoms into peroxy radicals, which convert nitric oxide (NO) to nitrogen dioxide (\[NO_{2}\]). These two then further react with a series of chemical reactions.  

Photochemical smog effects on environmental factors as well as human beings are huge. When the hydrocarbons in the atmosphere combine with the chemicals that are contained within the photochemical smog they form molecules that can cause eye irritation. The atmospheric radical stops the ground-level ozone from being eliminated by interfering with the nitrogen cycle. This ground-level ozone is very toxic for human beings. The other negative effects that are associated with the formation of photochemical smog is shortness of breath as well as decreasing vision.

  1. Sulfurous Smog is Also Known as London Smog- Sulfurous smog is also known as London smog because of a smog episode in London in the year 1952 to lead to the deaths of 4000 people. It is developed due to the high concentration of oxides of sulfur in the air. The emission of Sulfur dioxide by the natural source is estimated to be 24 persons whereas anthropogenic sources contribute to 76% of the emission of Sulfur dioxide. The fossil fuel sources that produce the sulfuric acid and a particular time lead to the choking mixture when it is incorporated into the droplets of fog. It is associated with actinic flux, high humidity as well as low temperature. During 1950 the legislation eliminated this form of air pollution due to the reduced emission of Sulfur dioxide and smoke before 1950 as it was considered a serious air pollutant that causes irritation to human eyes, nose, and lungs. Certain volcanoes also emit Sulfur dioxide in the atmosphere along with the fossil fuels like coal that bare sulfur.


Causes of Smog

The numerous sources such as factories, vehicles, and consumer products are the typical factors for the formation of pollutants that result in the development of smog. In the urban set up most of the smoke formation is the consequence of vehicle emission that sums up to 50% of smog. The relation between the weather patterns and heavy motor vehicle traffic, consumer products, and other industrial emissions is the main factor for the occurrence of smog. The consumer products include plastic packaging, paints, solvents, and sprays. Some of the main causes of the formation of smog are given below:-

  1. The Use of Coal is Fuel- Coal that is used for heating or power-producing plants results in the emission of high concentrations of sulfur oxides in the atmosphere. Also due to the presence of the high level of suspended particulate matter in the atmosphere and dampness, the effects due to the conversion of the coal also worsened. A smoggy environment is developed as the coal generates a significant amount of smoke while burning.

  2. Industrial and Vehicular Emissions- Fossil fuel combustion in cars, trucks, buses, motorbikes, and boats results in the emission from the transportation sector that becomes the chief contributor of smog. Most of the smoke formed in the urban setup is due to the emissions from the vehicles during peak traffic time. For the production of various materials and coals, the industrial process incorporates a large number of fossil fuels and resources that need to be extracted from nature. Therefore the industries also result in the emission of harmful gases and fumes that are released into the atmosphere which ultimately leads to the formation of smog.

  3. Excessive Waste Production- Our excessive consumption results in the production of a large amount of waste. To get rid of this huge amount of waste much of it is burned which leads to the emission of harmful gasses in the atmosphere which later transforms into smog.

  4. Fireworks- Though the use of fireworks is very limited and the occasions are very rare, a single night of firework display results in enormous air and particulate pollutants that leads to a significant amount of smog. This is associated with new year eves for Diwali where large amounts of fireworks are used. This results in the formation of a dense layer of smoke the very next day.

  5. Burning the Agricultural Material- In many of the countries the burning of the old crops are the waste materials that are generated from the farming practices is still prevalent. This leads to the major forms of smog. But the farmers still do this practice because it is convenient to do so. In capitals like Delhi, most of the smoke formation is due to crop fires. Every year thousands of farmers who are residing in North Indian states like Haryana Punjab in Uttar Pradesh bless their rice crop fields to grow wheat. The conversion of the agricultural materials also results in the burning of substances like fertilizers, ammonia, and pesticides that release certain gasses in our atmosphere which in later stages turn into smog.

  6. Activities in Construction- In the areas of high construction density, a large amount of dirt and dust particles enter into the air causing smoke that particularly orcas from construction activities.

  7. Natural Causes- Due to volcanic eruption and some specific plant life effects smog is developed due to natural causes as well. A high concentration of Sulphur dioxide is released during volcanic eruptions, particularly in the air, which is one of the primary constituents of smog formation. The radiocarbon amount of some of the plant’s life also results in the formation of smog in some areas.

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FAQs (Frequently Asked Questions)

1. How is smog formed?

The photochemical smog formation happens with the chemical reaction of sunlight, nitrogen oxides, and volatile organic compounds in the atmosphere and leaves the air-born particles and ground-level ozone. It depends both on the primary pollutants and the secondary pollutants.

2. What is the combination of smoke and fog called?

The combination of smoke and fog is called smog.

3. What is the difference between fog and smog?

Fog is generally caused by the water droplets in the air whereas smog is formed by the presence of particulates, smoke, and fog in the air. Breathing fog causes no harm as it is non-toxic. It only reduces visibility whereas breathing in smog causes lung cancer, asthma, breathing disorders as well as eye irritation.

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