User:Milton Beychok/Sandbox2

Smog is a type of air pollution and the word "smog" is a combination of  the words "smoke" and "fog". Modern smog is derived primarily from precursor pollutants, emitted to the atmosphere from vehicular internal combustion engines and industrial plants,  that react in the atmosphere with sunlight to produce secondary pollutants that also combine with the precursor emissions to form the components of photochemical smog.

Origin of the term "smog"
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 in London. The July 26, 1905 edition of the Daily Graphic, a London newspaper, 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'."&thinsp;

Photochemical smog


Originally, Dr. Des Voeux's term smog referred to a mixture of smoke, sulfur dioxide (SO2) and fog which was once prevalent in London when coal with a high sulfur content was widely used throughout the city as heating fuel. The dark, sulfurous London smog caused reduced visibility, respiratory problems and had a noticeable affect on human health. The so-called Great Smog of 1952 darkened the streets of London and killed approximately 4,000 people in a 4 day period (another 8,000 died from its effects in the following months). The type of smog experienced in London many decades ago is no longer encountered since other fuels have largely replaced the wide-spread use of high-sulfur coal for heating.

Photochemical smog is chemically quite different than the old London-type smog and has a long history. In 1542, when exploring what is now Southern California, Juan Rodriguez Cabrillo named San Pedro Bay the "Bay of Smokes" because of the thick haze that covered the area. Complaints of eye irritation from the polluted air in Los Angeles date back to the late 1860s. In the 1940s, photochemical smog first became apparent in Los Angeles and other large cities on sunny days, although none of those cities had any significant use of coal for heating fuel or for industrial activities. Photochemical smog is a daytime phenomenon characterized by a brown haze that reduces visibility and contains oxidants, such as ozone (O3), that cause respiratory problems, eye irritation and plants to be damaged. It is a mixture of ozone, reactive hydrocarbons, nitrogen oxide (NO), nitrogen dioxide (NO2), aldehydes, peroxyacetyl nitrate (PAN), particulate matter and other components..

The chemistry involved in the formation of smog is highly complex and involves many different reactions (see the adjacent diagram). The three major ingredients required to form photochemical smog are solar energy (i.e., sunlight), reactive hydrocarbons and nitrogen oxide, the latter two being referred to as the precursor pollutants. As shown in the adjacent diagram, the two precursors enter the atmosphere as gases emitted for the most part from vehicular internal combustion engines fuelled by gasoline and diesel oil. To a much lesser extent, nitrogen oxide is also emitted from industrial combustion sources, and reactive hydrocarbons are emitted by evaporation from the handling and storage of volatile hydrocarbons such as gasoline, solvents, some pesticides and some paints. Biogenic sources such as pine trees and certain other trees are also a relatively minor source of reactive hydrocarbon emissions such as isoprene and α-pinene.

Briefly,as depicted in the adjacent diagram, this a very simplified listing of the chemical reactions that take place to form photochemical smog:


 * The gaseous precursor nitrogen oxide, emitted primarily from vehicular internal combustion engines, is oxidized to produce gaseous nitrogen dioxide.
 * nitrogen oxide + oxygen $$\rightarrow$$ nitrogen dioxide
 * 2NO(g) + O2(g) $$\mathrm{\rightarrow}$$ 2NO2(g)


 * The gaseous nitrogen dioxide is broken down by solar energy from sunllght to produce gaseous nitrogen oxide and atomic oxygen (O, an oxygen radical).
 * '''nitrogen dioxide +solar energy $$\rightarrow$$ nitrogen oxide + atomic oxygen
 * NO2(g) + solar energy $$\rightarrow$$ NO (g) + O


 * The atomic oxygen reacts with gaseous atmospheric oxygen (O2) to form gaseous ozone (O3).
 * atomic oxygen + atmospheric oxygen $$\rightarrow$$ ozone
 * O + O2(g) $$\rightarrow$$ O3(g)


 * The gaseous ozone also oxidizes gaseous nitrogen oxide to form gaseous nitrogen dioxide and gaseous oxygen.
 * ozone + nitrogen oxide $$\rightarrow$$ nitrogen dioxide + oxygen
 * '''O3(g) + NO(g) $$\rightarrow$$ NO2(g) + O2(g)


 * The gaseous precursor reactive hydrocarbons (RH), emitted primarily from vehicular internal combustion engines, reacts with atomic oxygen, atmospheric oxygen and ozone to produce various highly reactive hydrocarbon free radicals (RO•2).


 * The hydrocarbon free radicals then react with other species such as nitrogen dioxide to form peroxyacetyl nitrate (PAN), aldehydes and other smog components.
 * Nitrogen dioxide + oxygen + hydrocarbon free radicals $$\rightarrow$$ peroxyacetyl nitrate
 * 2NO2(g) + O2(g) + 2RO•2 $$\rightarrow$$ 2CH3CO–OO–NO2(g)

The various products produced or formed from the precursor pollutants are referred to as secondary pollutants. All of the above chemical reactions (as well as others) occur more or less simultaneously during sunny, summertime days in most large cities with a great number of automobiles and other vehicles.

Health effects
Photochemical smog constitutes a serious health problem in most large cities. It is 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.

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.

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.

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, such as London, Atlanta, Houston, Phoenix, Las Vegas, New Delhi, New York, Cairo, Los Angeles, Sacramento, São Paulo, Mexico City, Santiago of Chile, Toronto, Athens, Beijing, Shanghai, Manila, Hong Kong, Seoul, the Randstad or Ruhr Area and can build up to dangerous levels.

London
In 1306, concerns over air pollution were sufficient for Edward I to (briefly) ban coal fires in London. 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 and 20th centuries 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 infamously 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 being double or even triple international standards.

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. The economic losses of the fires in 1997 have been estimated at more than US$9 billion. 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) has issued a daily rating since September 2003. The Indonesians have been ineffective at enforcing legal policies on errant farmers.

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.

United States
The United States Environmental Protection Agency has designated over 300 U.S. counties in the United States to be "non-attainment areas" for one or more air pollutants, meaning that they have failed to attain and maintain the National Ambient Air Quality Standards as required by the Clean Air Act enacted by the U.S. Congress. The non-attainment areas are largely clustered around large metropolitan areas, with the largest contiguous non-attainment zones being in California and the Northeast, as can be seen in the map below. Various U.S. and Canadian government agencies collaborate to produce real-time air quality maps and forecasts.

Los Angeles and the San Joaquin Valley
Being in low basins surrounded by mountains, Los Angeles and the San Joaquin Valley are notorious for their smog. The millions of vehicles in these basins plus the added effects of the San Francisco Bay and Los Angeles/Long Beach port complexes contribute to further air pollution. While strict regulations by the multiple California government agencies overseeing this problem have reduced the number of Stage 1 smog alerts from several hundred annually to just a few, these geologically predisposed entrapment zones collect pollution levels from cars, trucks and fixed sources which still exceeds health standards and is a pressing issue for the more than 25 million people who live there.

Major incidents in the US

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