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Smog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area and is caused by a mixture of smoke and sulfur dioxide.

Origin of term

Smog in New York City as viewed from the World Trade Center in 1988

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 26 July 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.”

"Smog" also appears in a Jan. 19, 1893, Los Angeles Times article and is attributed to "a witty English writer."

Health effects

Smog is a problem in a number of cities and continues to harm human health.[1] 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[2]. It can inflame breathing passages, decreasing the lungs' working capacity, and causing 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 [3].

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" [1]. The "very unhealthy" range for some other pollutants are: 355 μg m-3 - 424 μg m-3 for PM10; 15.5 ppbv - 30.4ppbv for CO and 0.65 ppbv - 1.24 ppbv for NO2[[2]

File:Lightmatter Golden gate bridge.jpg
Characteristic coloration for smog in California in the beige cloud bank behind Golden Gate Bridge

Areas affected

File:Beijing smog comparison August 2005.png
Beijing air on a day after rain (left) and a sunny but smoggy day (right)

Smog can form in almost any climate where industries or cities release large amounts of air pollution. 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, such as London, New York, Los Angeles, Mexico City, Houston, Toronto, Athens, Beijing, Hong Kong, the Randstad or Ruhr Area and can build up to dangerous levels.

Historically, there have been acute incidents where smog has killed thousands of people in a single metropolitan area.


Victorian London was notorious for its thick smogs, or "pea-soupers", a fact that is often recreated to add an air of mystery to a period costume drama

London has been known for smog since Roman times. In 1306, concerns over air pollution were sufficient for Edward I to (briefly) ban coal fires in London.[4] In 1661, John Evelyn's Fumifugium suggested burning fragrant wood instead of mineral coal, which he believed would reduce coughing. The Ballad of Gresham College the same year describes how the smoke "does our lungs and spirits choke, Our hanging spoil, and rust our iron."

Severe episodes of smog continued in the 19th century and were nicknamed "pea-soupers". The Great Smog of 1952 darkened the streets of London and killed approximately 4,000 people in the short time of 4 days (a further 8,000 died from its effects in the following weeks and months). Initially a flu epidemic was blamed for the loss of life. In 1956 the Clean Air Act introduced smokeless zones in the capital. Consequently, reduced sulfur dioxide levels made the intense and persistent London smog a thing of the past. It was after this the great clean-up of London began and buildings recovered their original stone façades which, during two centuries, had gradually blackened. Smog caused by traffic pollution, however, does occur in modern London.

Mexico City

Due to its location in a highland 'bowl', cold air sinks down onto the urban area of Mexico City, trapping industrial and vehicle pollution underneath, and turning it into the most infamous smog-plagued city of Latin America. Within one generation, the city has changed from being known for some of the cleanest air of the world into one with some of the worst pollution, with pollutants like nitrogen dioxide breaching international health standards by 2-3 times.[5]

Los Angeles

Being in a low basin surrounded by mountains, Los Angeles is a notorious victim of smog. The millions of vehicles in the city due to lack of sufficient public transportation, plus the added affects of the Los Angeles/Long Beach port complex contribute to further air pollution in the city. While strict regulations by the Californian government have reduced the number of Stage 1 smog alerts from several hundred annually to just a few annually, Los Angeles' pollution level still exceeds health standards and is a pressing issue for the more than 15 million people who live there.


In December 2005, schools and public offices had to close in Tehran, Iran and 1600 people were taken to hospital, in a severe smog blamed largely on unfiltered car exhaust.[6]

United States

The United States Environmental Protection Agency has designated over 300 U.S. counties to be non-attainment areas for one or more pollutants tracked as part of the National Ambient Air Quality Standards.[7] These areas are largely clustered around large metropolitan areas, with the largest contiguous non-attainment zones in California and the Northeast. Various U.S. and Canadian government agencies collaborate to produce real-time air quality maps and forecasts.[8]

Major incidents in the US

  • 1948, October 30-31, Donora, PA: 20 died, 600 hospitalized, thousands more stricken. Lawsuits were not settled until 1951.[9]
  • 1953, November, New York: Smog kills between 170 and 260 people.[10]
  • 1954, October, Los Angeles: heavy smog shuts down schools and industry for most of the month.[11]
  • 1963, New York: blamed for 200 deaths [12]
  • 1966, New York: blamed for 169 deaths [13]

Photochemical smog

In the 1950s a new type of smog, known as photochemical smog, was first described. This forms when sunlight hits various pollutants in the air and forms a mix of inimicial chemicals that can be very dangerous. A photochemical smog is the chemical reaction of sunlight, nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the atmosphere, which leaves airborne particles (called particulate matter) and ground-level ozone.

Nitrogen oxides are released by nitrogen and oxygen in the air reacting together under high temperature such as in the exhaust of fossil fuel-burning engines in cars, trucks, coal power plants, and industrial manufacturing factories. VOCs are released from anthropogenic (man-made) sources such as gasoline, paints, solvents, pesticides, and biogenic sources, such as pine and citrus tree emissions.

This noxious mixture of air pollutants can include the following:

All of these 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.[14] Because it travels with the wind, it can affect sparsely populated areas as well.

Southeast Asia

Smog is a regular problem in Southeast Asia caused by land and forest fires in Indonesia, especially Sumatra and Kalimantan, although the less political term haze is preferred in describing the problem. Farmers and plantation owners are usually responsible for the fires, which they use to clear tracts of land for further plantings. Those fires mainly affect Brunei, Indonesia, Philippines, Malaysia, Singapore and Thailand, and occasionally Guam and Saipan[3] [4] The economic losses of the fires in 1997 have been estimated at US$9.3 billion [5]. This includes damages in agriculture production, destruction of forest lands, health, transportation, tourism, and other economic endeavours. Not included are social, environmental, and psychological problems and long-term health effects. The latest bout of haze to occur in Malaysia, Singapore and the Malacca Straits is in October 2006, and was caused by smoke from fires in Indonesia being blown across the Straits of Malacca by south-westerly winds.

The Association of Southeast Asian Nations (ASEAN) reacted and signed Agreement on Transboundary Haze Pollution, formed a Regional Haze Action Plan (RHAP) and established a co-ordination and support unit (CSU). RHAP, with the help of Canada, established a monitoring and warning system for forest/vegetation fires and implemented a Fire Danger Rating System (FDRS). The Malaysian Meteorological Service (MMS) [6] has issued a daily rating since September 2003. The Indonesians have been ineffective at enforcing legal policies on errant farmers.

Natural causes

An erupting volcano can also emit high levels of sulfur dioxide, creating volcanic smog, or vog.

Pollution index

File:295189351 304eb88223 b.jpg
Smog fills the skies of Delhi, India. Measures like CNG-run buses and Delhi Metro have decreased the pollution-level of the city

The severity of smog is often measured using automated optical instruments such as Nephelometers, as haze is associated with visibility and traffic control in ports. Haze however can also be an indication of poor air quality though this is often better reflected using accurate purpose built air indexes such as the American Air Quality Index, the Malaysian API (Air Pollution Index) and the Singaporean Pollutant Standards Index.

In hazy conditions, it is likely that the index will report the suspended particulate level. The disclosure of the responsible pollutant is mandated in some jurisdictions.

The American AQI is divided into six color coded categories. Technically AQI runs only from 0 to 500. The 301 to 500 range is categorised as hazardous and colored maroon. [7]

The Malaysian API does not have a capped value; hence its most hazardous readings can go above 500. Above 500, a state of emergency is declared in the affected area. Usually, this means that non-essential government services are suspended, and all ports in the affected area are closed. There may also be prohibitions on private sector commercial and industrial activities in the affected area excluding the food sector. So far, state of emergency rulings due to hazardous API levels were applied to the Malaysian towns of Port Klang, Kuala Selangor and the state of Sarawak during the 2005 Malaysian haze and the 1997 Southeast Asian haze.

Cultural references

File:Claude Monet 015.jpg
Claude Monet made several trips to London between 1899 and 1901, during which he painted views of the Thames and Houses of Parliament which show the sun struggling to shine through London's smog-laden atmosphere
  • The London "pea-soupers" earned the capital the nickname of "The Smoke". Similarly, Edinburgh was known as "Auld Reekie". The smogs feature in many London novels as a motif indicating hidden danger or a mystery, perhaps most overtly in Margery Allingham's The Tiger in the Smoke (1952), but also in Dickens' Bleak House (1852):

[A]s he handed me into a fly after superintending the removal of my boxes, I asked him whether there was a great fire anywhere? For the streets were so full of dense brown smoke that scarcely anything was to be seen.
"Oh, dear no, miss," he said. "This is a London particular."
I had never heard of such a thing.
"A fog, miss," said the young gentleman.

  • The 1970 made-for-TV movie A Clear and Present Danger, which featured Hal Holbrook, E.G. Marshall, Joseph Campanella, Jack Albertson and Pat Hingle, was one of the first American television network entertainment programs to warn about the problem of smog and air pollution.[15] (This film is not to be confused with the 1994 film with a similar name.)
  • 'Smog' or 'Smoggy' has also come into use to describe a resident of Teesside (in North East England) or a supporter of Middlesbrough Football Club, due to the high concentration of chemical and heavy industry in the Teesside area. Although it has now been proven that the Teesside air is cleaner than London, Newcastle, Sunderland and many other British cities, the main source of pollution in the air is now vehicle exhaust fumes, like most urban areas.
  • Hedorah, a monster from the Godzilla movie, Godzilla vs. Hedorah, feeds on pollution and is referred to as "The Smog Monster".

See also

Notes and references

  1. USA Today
  2. "Who is most at risk from ozone?"
  3. Ozone in Wisconsin
  5. Air pollution in Mexico City, University of Salzburg
  6. "Hundreds treated over Tehran smog". BBC News. 2005-12-10. Retrieved 2006-08-03.
  7. The Green Book Nonattainment Areas | Green Book | US EPA
  8. Available at
  9. Environmental History Timeline: 1940-1960
  10. Environmental History Timeline: 1940-1960
  11. Environmental History Timeline: 1940-1960
  14. Miller, Jr., George Tyler (2002). Living in the Environment: Principles, Connections, and Solutions (12th Edition). Belmont: The Thomson Corporation. pp. p. 423. ISBN 0-534-37697-5.
  15. A Clear and Present Danger (1970) (TV)

External links

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