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Smog is a type of air pollutant. The word "smog" was coined in the early 20th century as a portmanteau of the words smoke and fog to refer to smoky fog, its opacity, and odour. The word was then intended to refer to what was sometimes known as pea soup fog, a familiar and serious problem in London from the 19th century to the mid 20th century. This kind of visible air pollution is composed of nitrogen oxides, sulphur oxides, ozone, smoke or particulates among others (less visible pollutants include carbon monoxide, CFCs and radioactive sources). Human-made smog is derived from coal emissions, vehicular emissions, industrial emissions, forest and agricultural fires and photochemical reactions of these emissions. Modern smog, as found for example in Los Angeles, is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog. In certain other cities, such as Delhi, smog severity is often aggravated by stubble burning in neighboring agricultural areas. The atmospheric pollution levels of Los Angeles, Beijing, Delhi, Lahore, Mexico City, Tehran and other cities are increased by inversion that traps pollution close to the ground. It is usually highly toxic to humans and can cause severe sickness, shortened life or death.


Coinage of the term "smog" is generally attributed to Dr. Henry Antoine Des Voeux in his 1905 paper, "Fog and Smoke" for a meeting of the Public Health Congress. The July 26, 1905 edition of the London newspaper Daily Graphic quoted Des Voeux, "He said it required no science to see that there was something produced in great cities which was not found in the country, and that was smoky fog, or what was known as 'smog'." The following day the newspaper stated that "Dr. Des Voeux did a public service in coining a new word for the London fog." However, this is predated by a Los Angeles Times article of January 19, 1893, in which the word is attributed to "a witty English writer."



Coal fires, used to heat individual buildings or in a power-producing plant, can emit significant clouds of smoke that contributes to smog. Air pollution from this source has been reported in England since the Middle Ages. London, in particular, was notorious up through the mid-20th century for its coal-caused smogs, which were nicknamed ' pea-soupers.' Air pollution of this type is still a problem in areas that generate significant smoke from burning coal. The emissions from coal combustions are one of the main causes of air pollution in China. Especially during autumn and winter when coal-fired heating ramps up, the amount of produced smoke forces some Chinese cities to close down roads, schools or airports. One prominent example for this was China's Northeastern city Harbin in 2013.

Transportation emissions

Traffic emissions – such as from trucks, buses, and automobiles – also contribute. Airborne by-products from vehicle exhaust systems cause air pollution and are a major ingredient in the creation of smog in some large cities.}} The major culprits from transportation sources are carbon monoxide (CO), nitrogen oxides (NO and NOx), volatile organic compounds, sulfur dioxide, and hydrocarbons. (Hydrocarbons are the main components of petroleum fuels such as gasoline and diesel fuel.) These molecules react with sunlight, heat, ammonia, moisture, and other compounds to form the noxious vapors, ground level ozone, and particles that comprise smog.

Photochemical smog

Photochemical smog is the chemical reaction of sunlight, nitrogen oxides and volatile organic compounds in the atmosphere, which leaves airborne particles and ground-level ozone. }} This noxious mixture of air pollutants may include the following: A primary pollutant is an air pollutant emitted directly from a source. A secondary pollutant is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere. Examples of a secondary pollutant include ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight; nitrogen dioxide (NO2), which is formed as nitric oxide (NO) combines with oxygen in the air; and acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water.http://www.pmfias.com/2015/08/Smog-Photochemical-smog.html All of these harsh chemicals are usually highly reactive and oxidizing. Photochemical smog is therefore considered to be a problem of modern industrialization. It is present in all modern cities, but it is more common in cities with sunny, warm, dry climates and a large number of motor vehicles. Because it travels with the wind, it can affect sparsely populated areas as well. The composition and chemical reactions involved in photochemical smog were not understood until the 1950s. In 1948, flavor chemist Arie Haagen-Smit adapted some of his equipment to collect chemicals from polluted air, and identified ozone as a component of Los Angeles smog. Haagen-Smit went on to discover that nitrous oxides from automotive exhausts and gaseous hydrocarbons from cars and oil refineries, exposed to sunlight, were key ingredients in the formation of ozone and photochemical smog. Haagen-Smit worked with Arnold Beckman, who developed various equipment for detecting smog, ranging from an "Apparatus for recording gas concentrations in the atmosphere" patented on October 7, 1952, to "air quality monitoring vans" for use by government and industry.

Natural causes

An erupting volcano can also emit high levels of sulphur dioxide along with a large quantity of particulate matter; two key components to the creation of smog. However, the smog created as a result of a volcanic eruption is often known as vog to distinguish it as a natural occurrence. The radiocarbon content of some plant life has been linked to the distribution of smog in some areas. For example, the creosote bush in the Los Angeles area has been shown to have an effect on smog distribution that is more than fossil fuel combustion alone.

Health effects

wearing smog-gas masks at banquet, Los Angeles, circa 1954]] Smog is a serious problem in many cities and continues to harm human health. Ground-level ozone, sulfur dioxide, nitrogen dioxide and carbon monoxide are especially harmful for senior citizens, children, and people with heart and lung conditions such as emphysema, bronchitis, and asthma. It can inflame breathing passages, decrease the lungs' working capacity, cause shortness of breath, pain when inhaling deeply, wheezing, and coughing. It can cause eye and nose irritation and it dries out the protective membranes of the nose and throat and interferes with the body's ability to fight infection, increasing susceptibility to illness. Hospital admissions and respiratory deaths often increase during periods when ozone levels are high. There is a lack of knowledge on the long-term effects of air pollution exposure and the origin of asthma. An experiment was carried out using intense air pollution similar to that of the 1952 Great Smog of London. The results from this experiment concluded that there is a link between early-life pollution exposure that leads to the development of asthma, Proposing the ongoing effect of the Great Smog.

Levels of unhealthy exposure

The U.S. EPA has developed an Air Quality Index to help explain air pollution levels to the general public. 8 hour average ozone concentrations of 85 to 104 ppbv are described as "Unhealthy for Sensitive Groups", 105 ppbv to 124 ppbv as "unhealthy" and 125 ppb to 404 ppb as "very unhealthy". The "very unhealthy" range for some other pollutants are: 355 μg m−3 – 424 μg m−3 for PM10; 15.5 ppm – 30.4ppm for CO and 0.65 ppm – 1.24 ppm for NO2.}}

Premature deaths due to cancer and respiratory disease

In 2016, the Ontario Medical Association announced that smog is responsible for an estimated 9,500 premature deaths in the province each year. A 20-year American Cancer Society study found that cumulative exposure also increases the likelihood of premature death from a respiratory disease, implying the 8-hour standard may be insufficient. NPR.org, Smoggy Skies May Cause Respiratory Death

Alzheimer risk

Tiny magnetic particles from air pollution have for the first time been discovered to be lodged in human brains– and researchers think they could be a possible cause of Alzheimer’s disease. Researchers at Lancaster University found abundant magnetite nanoparticles in the brain tissue from 37 individuals aged three to 92-years-old who lived in Mexico City and Manchester. This strongly magnetic mineral is toxic and has been implicated in the production of reactive oxygen species (free radicals) in the human brain, which are associated with neurodegenerative diseases including Alzheimer’s disease.http://www.lancaster.ac.uk/news/articles/2016/toxic-air-pollution-nanoparticles-discovered-in-the-human-brain/ http://m.motherjones.com/environment/2015/05/air-pollution-dementia-alzheimers-brain

Smog and the risk of certain birth defects

A study examining 806 women who had babies with birth defects between 1997 and 2006, and 849 women who had healthy babies, found that smog in the San Joaquin Valley area of California was linked to two types of neural tube defects: spina bifida (a condition involving, among other manifestations, certain malformations of the spinal column), and anencephaly (the underdevelopment or absence of part or all of the brain, which if not fatal usually results in profound impairment).

Smog and low birth weight

According to a study published in The Lancet, even a very small (5 μg) change in PM2.5 exposure was associated with an increase (18%) in risk of a low birth weight at delivery, and this relationship held even below the current accepted safe levels.

Areas affected

Smog can form in almost any climate where industries or cities release large amounts of air pollution, such as smoke or gases. However, it is worse during periods of warmer, sunnier weather when the upper air is warm enough to inhibit vertical circulation. It is especially prevalent in geologic basins encircled by hills or mountains. It often stays for an extended period of time over densely populated cities or urban areas, and can build up to dangerous levels.


According to the Canadian Science Smog Assessment published in 2012, smog is responsible for detrimental effects on human and ecosystem health, as well as socioeconomic well-being across the country. It was estimated that the province of Ontario sustains $201 million in damages annually for selected crops, and an estimated tourism revenue degradation of $7.5 million in Vancouver and $1.32 million in The Fraser Valley due to decreased visibility. Air pollution in British Columbia is of particular concern, especially in the Fraser Valley, because of a meteorological effect called Inversion which decreases air dispersion and leads to smog concentration.
"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Smog, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Smog&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany