Smog
From Wikipedia, the free encyclopedia
- For other uses, see Smog (disambiguation)
Smog is a kind of air pollution the name 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 sulphur dioxide. In the 1950s a new type of smog, known as photochemical smog, was first described. This is a noxious mixture of air pollutants including the following:
- nitrogen oxides, such as nitrogen dioxide
- tropospheric ozone
- volatile organic compounds (VOCs)
- peroxyacyl nitrates (PAN)
- aldehydes (R'O)
All of these chemicals are usually highly reactive and oxidizing. Due to this fact, photochemical smog is considered to be a problem of modern industrialization.
Photochemical smog is a concern in most major urban centres but, because it travels with the wind, it can affect sparsely populated areas as well. Smog is caused by a reaction between sunlight and emissions mainly from human activity. Photochemical smog is the chemical reaction of sunlight, nitrogen oxides (NOx) and volatile organic compounds (VOC's) in the atmosphere, which leaves airborne particles (called particulate matter) and ground-level ozone. Nitrogen oxides are released in the exhaust of fossil fuel-burning engines in cars, trucks, coal power plants, and industrial manufacturing factories. VOC's are vapors released from gasoline, paints, solvents, pesticides, and other chemicals.
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[edit] Origin of term
The term "smog" was first coined by 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, “[H]e 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.”
[edit] Areas affected
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, such as London, Los Angeles, Mexico City, Houston, Toronto, Athens, Beijing, Hong Kong or the Ruhr Area and can build up to dangerous levels.
[edit] London
London has been known for smog since Roman times. Even in the Middle Ages, concerns over air pollution were sufficient for Edward I to (briefly) ban the use |Ballad of Gresham College]] the same year describes how the smoke "does our lungs and spirits choke, Our hanging spoil, and rust our iron."
Episodes of smog became common in London in the late 19th century and were nicknamed "pea-soupers". The Great Smog of 1952 darkened the streets London and killed approximately 4,000 people in the short term (a further 8,000 died from its effects in the following weeks and months). Reluctant to admit that coal smoke was to blame, the British government initially blamed a flu epidemic. In 1956 the Clean Air Act introduced smokeless zones to the capital. This was only seriously enforced after the December 1957 smog which killed many elderly persons in the capital and suburbs.[citation needed] It may be coincidence but an exceptional epidemic of Asian flu was equally virulent at the time of the 1957 smog. Finally only smokeless fuels could be used in these areas. 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.
[edit] 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.[1]
[edit] Tehran
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.[2]
[edit] Aviation Smog
High altitude ice clouds (cirrus clouds) which result from air traffic can be seen as a kind of smog. Their climatic impact is not well understood yet and is investigated in numerous studies. Ice clouds caused by aviation act like an 'ice curtain' that is being weaved around the world. Although it prevents solar radiation from reaching the Earth's surface, it reflects outgoing infrared radiation to a higher extent. The net effect is that more heat energy is trapped within the Earth's atmosphere contributing to global warming.
[edit] Health effects
Smog is a problem in a number of cities and continues to harm human health.[3] Ground-level ozone is especially harmful for senior citizens, children, and people with heart and lung conditions such as emphysema, bronchitis, and asthma[4]. It can inflame breathing passages, decreasing the lung's 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 [5].
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 - 30.4ppb for CO and 0.65 ppbv - 1.24 [2]
[edit] Natural causes
An erupting volcano can also emit high levels of sulfur dioxide, creating volcanic smog, or vog.
The burning of forests in Indonesia has on a number of occasions created prolonged smog-like haze, which have extended to parts of Malaysia, Philippines, Singapore and Thailand although a lot of the times these fires are started by farmers who want to clear away land for the start of the new planting season.
[edit] Cultural references
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.
— Dickens, Bleak House
'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.
[edit] See also
[edit] Notes and references
- ^ Air pollution in Mexico City, University of Salzburg
- ^ "Hundreds treated over Tehran smog", BBC News, 2005-12-10. Retrieved on 2006-08-03.
- ^ USA Today
- ^ "Who is most at risk from ozone?"
- ^ Ozone in Wisconsin
- "When smog was a frequent occurrence" WW2 People's War, BBC 2005-08-10. Accessed 2006-08-03.
