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Types of chocolate
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Chocolate most commonly comes in dark (bottom), milk (middle), and white (top) varieties, with cocoa solids contributing to the brown coloration.
Chocolate is a range of foods derived from cocoa (cacao), mixed with fat (e.g., cocoa butter) and finely powdered sugar to produce a solid confectionery. There are several types of chocolate, classified according to the proportion of cocoa used in a particular formulation.
The use of particular name designations is sometimes subject to international governmental regulation. Some governments assign chocolate solids and ranges of chocolate differently.
Contents
[hide]
1 Terminology
2 Types
2.1 By country/region
2.1.1 United States
2.1.2 Canada
2.1.3 European Union
2.1.4 Japan
3 Definition
4 Quality
5 See also
6 References
7 External links
Terminology[edit]
The cocoa bean (or other alternative) products from which chocolate is made are known under different names in different parts of the world. In the American chocolate industry:
chocolate liquor is the ground or melted state of the nib of the cacao bean, containing roughly equal parts cocoa butter and solids.
cocoa butter is the fatty component of the bean.
cocoa solids is the remaining nonfat part of the cocoa bean, which is ground into a powder.[1]
Types[edit]
Different forms and flavors of chocolate are produced by varying the quantities of the different ingredients. Other flavours can be obtained by varying the time and temperature when roasting the beans.
Swiss Milk chocolate
Milk chocolate is solid chocolate made with milk, in the form of milk powder, liquid milk, or condensed milk, added. In 1875, Swiss confectioner Daniel Peter, in cooperation with his neighbour Henri Nestlé in Vevey, developed the first solid milk chocolate using condensed milk. The bar was named "Gala Peter", combining the Greek word for "milk" and his name.[2] A German company Jordan & Timaeus in Dresden, Saxony had already invented milk chocolate in 1839;[3] hitherto it had only been available as a drink.[4] The US Government requires a 10% concentration of chocolate liquor. EU regulations specify a minimum of 25% cocoa solids. However, an agreement was reached in 2000 that allowed what by exception from these regulations is called "milk chocolate" in the UK, Ireland, and Malta, containing only 20% cocoa solids, to be traded as "family milk chocolate" elsewhere in the European Union.[5]
Cadbury chocolate is the brand leader in the United Kingdom.[6] First produced by George Cadbury Junior in 1905, Cadbury Dairy Milk was made with a higher proportion of milk than previous chocolate bars, and it became the company's best selling product by 1914. It is the best selling milk chocolate bar in the UK, followed by Galaxy.[7]
"Hershey process" milk chocolate is popular in the US. The process was invented by Milton S. Hershey, founder of The Hershey Company. The process uses fresh milk from local farms. The logistics of purchasing and delivering fresh milk is difficult as, according to state regulations fresh milk cannot be held for more than 72 hours after its reception. If not immediately processed into milk chocolate, the milk must be disposed of. The actual Hershey process is a trade secret, but experts speculate that the milk is partially lipolyzed, producing butyric acid, and then the milk is pasteurized and stabilized. This process gives the product a particular taste, to which the US public has shown to have an affinity, to the extent that some rival manufacturers now add butyric acid to their milk chocolates.[4]
Dark chocolate, also known as "plain chocolate" or "black chocolate", is produced using higher percentages of cocoa, traditionally with cocoa butter instead of milk, but there are also dark milk chocolates and many degrees of hybrids. Dark chocolate can be eaten as is, or used in cooking, for which thicker, baking bars, usually with high cocoa percentages ranging from 70% to 99% are sold. Dark is synonymous with semisweet, and extra dark with bittersweet, although the ratio of cocoa butter to solids may vary.
Swiss White chocolate
White chocolate is made of sugar, milk, and cocoa butter, without the cocoa solids.
A 200 gram bar of dark baking chocolate, with a minimum cocoa content of 40%
Swiss dark chocolate
Cocoa powder is used for baking, and for drinking with added milk and sugar. There are two types of unsweetened cocoa powder: natural cocoa (like the sort produced by the Broma process), and Dutch-process cocoa. Both are made by pulverizing partially defatted chocolate liquor and removing nearly all the cocoa butter; Dutch-process cocoa is additionally processed with alkali to neutralize its natural acidity. Natural cocoa is light in colour and somewhat acidic with a strong chocolate flavor. Natural cocoa is commonly used in recipes that also use baking soda; as baking soda is an alkali, combining it with natural cocoa creates a leavening action that allows the batter to rise during baking. Dutch cocoa is slightly milder in taste, with a deeper and warmer colour than natural cocoa. Dutch-process cocoa is frequently used for chocolate drinks such as hot chocolate due to its ease in blending with liquids. However, Dutch processing destroys most of the flavonoids present in cocoa.[8] In 2005 Hershey discontinued their pure Dutch-process European Style cocoa and replaced it with Special Dark, a blend of natural and Dutch-process cocoa.
Organic chocolate is chocolate which has been certified organic ingredients.
Raw chocolate is chocolate that has not been processed, heated, or mixed with other ingredients. It is sold in chocolate-growing countries, and to a much lesser extent in other countries, often promoted as healthy.[9]
Unsweetened chocolate, also known as bitter, baking chocolate, or cooking chocolate, is pure chocolate liquor mixed with some form of fat to produce a solid substance. The pure, ground, roasted cocoa beans impart a strong, deep chocolate flavor. With the addition of sugar, however, it is used as the base for cakes, brownies, confections, and cookies.
Bittersweet chocolate is chocolate liquor (or unsweetened chocolate) to which some sugar (less than a third), more cocoa butter, vanilla flavouring, and sometimes lecithin has been added. It typically has less sugar and more liquor than semisweet chocolate,[10] but the two are interchangeable when baking. Bittersweet and semisweet chocolates are sometimes referred to as "couverture". Many brands now print on the package the percentage of cocoa in the chocolate (as chocolate liquor and added cocoa butter). The higher the percentage of cocoa, the less sweet the chocolate is.
Semisweet chocolate is frequently used for cooking purposes. It is a dark chocolate with (by definition in Swiss usage) half as much sugar as cocoa, beyond which it is "sweet chocolate". Semisweet chocolate does not contain milk solids.[11]
"Couverture" is a term used for chocolates rich in cocoa butter. Popular brands of couverture used by professional pastry chefs and often sold in gourmet and specialty food stores include: Valrhona, Felchlin, Lindt & Sprüngli, Scharffen Berger, Cacao Barry, Callebaut, Chocodate, Chocofig fuel chocolates, and Guittard. These chocolates contain a high percentage of cocoa.
Semi-sweet chocolate chips
Tempered couverture chocolate
Pieces of dark compound chocolate cake coating
"Compound chocolate" is the technical term for a confection combining cocoa with vegetable fat, usually tropical fats and/or hydrogenated fats, as a replacement for cocoa butter. It is often used for candy bar coatings. In many countries it may not legally be called "chocolate".
Modeling chocolate is a chocolate paste made by melting chocolate and combining it with corn syrup, glucose syrup, or golden syrup. It is primarily used by cakemakers and pâtisseries to add decoration to cakes and pastries.
Ruby chocolate is a new type of chocolate, created by Barry Callebaut. The variety was in development beginning in 2004. The new chocolate type is made from the Ruby cocoa bean, through a process that is said to unlock the flavor and color tone present in the Ruby bean. The chocolate's taste is described as "sweet yet sour".[citation needed]
Flavours such as mint, vanilla, coffee, orange, or strawberry are sometimes added to chocolate in a creamy form or in very small pieces. Chocolate bars frequently contain added ingredients such as peanuts, nuts, fruit, caramel, and crisped rice. Pieces of chocolate, in various flavours, are sometimes added to cereals and ice cream.
By country/region[edit]
United States[edit]
The U.S. Food and Drug Administration (FDA) regulates the naming and ingredients of cocoa products:[12][13]
Product
Chocolate Liquor
Milk Solids
Sugar
Cocoa Fat
Milk Fat
Milk Chocolate ≥ 10% ≥ 12%
Sweet Chocolate ≥ 15% < 12%
Semisweet or Bittersweet (Dark) Chocolate ≥ 35% < 12%
White Chocolate ≥ 14% ≤ 55% ≥ 20% ≥ 3.5%
In March 2007, the Chocolate Manufacturers Association, whose members include Hershey's, Nestlé, and Archer Daniels Midland, began lobbying the U.S. Food and Drug Administration (FDA) to change the legal definition of chocolate to allow the substitution of "safe and suitable vegetable fats and oils" (including partially hydrogenated vegetable oils) for cocoa butter in addition to using "any sweetening agent" (including artificial sweeteners) and milk substitutes.[14] Currently, the FDA does not allow a product to be referred to as "chocolate" if the product contains any of these ingredients.[15] To work around this restriction, products with cocoa substitutes are often branded or labeled as "chocolatey" or as in the case of Hershey's Mr. Goodbar containing vegetable oils, "made with chocolate".
Canada[edit]
The legislation for cocoa and chocolate products in Canada is found in Division 4 of the Food and Drug Regulations (FDR), under the Food and Drugs Act (FDA). The Canadian Food Inspection Agency (CFIA) is responsible for the administration and enforcement of the FDR and FDA (as it relates to food).[16]
Product
Cocoa Butter
Milk Solids
Milk Fat
Fat-Free Cocoa Solids
Cocoa Solids
Milk Chocolate ≥ 15% ≥ 12% ≥ 3.39% ≥ 2.5% ≥ 25%
Sweet Chocolate ≥ 18% < 12% ≥ 12% ≥ 31%
Chocolate, Bittersweet Chocolate, Semi-sweet Chocolate or Dark Chocolate ≥ 18% < 5% ≥ 14% ≥ 35%
White Chocolate ≥ 20% ≤ 14% ≥ 3.5%
The use of cocoa butter substitutes in Canada is not permitted. Chocolate sold in Canada cannot contain vegetable fats or oils.[17]
The only sweetening agents permitted in chocolate in Canada are listed in Division 18 of the Food and Drug Regulations.[18] Artificial sweeteners such as aspartame, sucralose, acesulfame potassium, and sugar alcohols (sorbitol, maltitol, etc.) are not permitted.
Products manufactured or imported into Canada that contain non-permitted ingredients (vegetable fats or oils, artificial sweeteners) cannot legally be called "chocolate" when sold in Canada. A non-standardized name such as "candy" must be used.[17]
European Union[edit]
Products labelled as "Family Milk Chocolate" elsewhere in the European Union are permitted to be labelled as simply "Milk Chocolate" in Malta, the U.K. and the Republic of Ireland.[19]
Product
Total Dry Cocoa Solids
Cocoa Butter
Non-Fat Cocoa Solids
Total Fat
Milk Fat
Milk Solids
Flour/starch
Chocolate ≥ 35% ≥ 18% ≥ 14%
Couverture Chocolate ≥ 35% ≥ 31% ≥ 2.5%
Chocolate Vermicelli or Flakes ≥ 32% ≥ 12% ≥ 14%
Milk Chocolate ≥ 25% ≥ 2.5% ≥ 25% ≥ 3.5% ≥ 14%
Couverture Milk Chocolate ≥ 25% ≥ 2.5% ≥ 31% ≥ 3.5% ≥ 14%
Milk Chocolate Vermicelli or Flakes ≥ 20% ≥ 2.5% ≥ 12% ≥ 3.5% ≥ 12%
Family Milk Chocolate ≥ 20% ≥ 2.5% ≥ 25% ≥ 5% ≥ 20%
Cream Chocolate ≥ 25% ≥ 2.5% ≥ 25% ≥ 5.5% ≥ 14%
Skimmed Milk Chocolate ≥ 25% ≥ 2.5% ≥ 25% ≤ 1% ≥ 14%
White Chocolate ≥ 20% ≥ 14%
Chocolate a la taza ≥ 35% ≥ 18% ≥ 14% ≤ 8%
Chocolate familiar a la taza ≥ 30% ≥ 18% ≥ 12% ≤ 18%
Note 1: "Total Fat" refers to the combined cocoa butter and milk fat content.
Note 2: "Total Dry Cocoa Solids" as defined in this and all world regulations refers to combined cocoa powder and butter.
Japan[edit]
In Japan, 'chocolate products' are classified on a complex scale (q.v. ja:チョコレート#チョコレートの規格).
Chocolate materials (チョコレート生地, chokorēto kiji):
Pure chocolate material (純チョコレート生地, jun-chokorēto kiji)
Cocoa content ≥35%, cocoa butter ≥18%, sucrose ≤55%, lecithin ≤0.5%, no additives other than lecithin and vanilla flavouring, no fats other than cocoa butter and milk fats, water ≤3%
Pure milk chocolate material (純ミルクチョコレート生地, jun-miruku chokorēto kiji)
Cocoa content ≥21%, cocoa butter ≥18%, milk solids ≥14%, milk fats ≥3.5%, sucrose ≤55%, lecithin ≤0.5%, no additives other than lecithin and vanilla flavouring, no fats other than cocoa butter and milk fats, water ≤3%
Chocolate material (チョコレート生地, chokorēto kiji)
Cocoa content ≥35%, cocoa butter ≥18%, water ≤3%. It is also permitted to substitute milk solids for cocoa content as follows: cocoa content ≥21%, cocoa butter ≥18%, combined milk solids & cocoa content ≥35%, milk fats ≥3%, water ≤3%.
Milk chocolate material (ミルクチョコレート生地, miruku chokorēto kiji)
Cocoa content ≥21%, cocoa butter ≥18%, milk solids ≥14%, milk fats ≥3%, water ≤3%
Quasi chocolate material (準チョコレート生地, jun-chokorēto kiji) a
Cocoa content ≥15%, cocoa butter ≥3%, fats ≥18%, water ≤3%
Quasi milk chocolate material (準ミルクチョコレート生地, jun-miruku chokorēto kiji)
Cocoa content ≥7%, cocoa butter ≥3%, fats ≥18%, milk solids ≥12.5%, milk fats ≥2%, water ≤3%
Chocolate products (チョコレート製品, chokorēto seihin):
Products using milk chocolate or quasi milk chocolate as described above are handled in the same way as chocolate / quasi chocolate.
Chocolate (チョコレート, chokorēto)
Processed chocolate products made from chocolate material itself or containing at least 60% chocolate material. Processed chocolate products must contain at least 40% chocolate material by weight. Amongst processed chocolate products, those containing at least 10% by weight of cream and no more than 10% of water can be called raw chocolate (生チョコレート, nama chokorēto)
Chocolate sweet (チョコレート菓子, chokorēto kashi)
Processed chocolate products containing less than 60% chocolate material
Quasi chocolate (準チョコレート, jun-chokorēto)
The Quasi symbol should officially be circled. Processed quasi chocolate products made from quasi chocolate material itself or containing at least 60% quasi chocolate material.
Quasi chocolate sweet (準チョコレート菓子, jun-chokorēto kashi)
Processed quasi chocolate products containing less than 60% quasi chocolate material
Definition[edit]
Chocolate is a product based on cocoa solid or cocoa fat or both. The amount and types of cocoa solids and fat that the term implies is a matter of controversy. Manufacturers have an incentive to use the term for variations that are cheaper to produce, containing less cocoa and more cocoa substitutes.
There has been disagreement in the EU about the definition of chocolate; this dispute covers several ingredients, including the types of fat used and the quantity of cocoa. In 1999, however, the EU resolved the fat issue by allowing up to 5% of chocolate's content to be one of 5 alternatives to cocoa butter: illipe oil, palm oil, sal, shea butter, kokum gurgi, or mango kernel oil.[20]
A recent workaround has been to reduce the amount of cocoa butter in candy bars without using vegetable fats by adding polyglycerol polyricinoleate (PGPR), which is an artificial castor oil-derived emulsifier that simulates the mouthfeel of fat. Up to 0.3% PGPR may be added to chocolate for this purpose.[21]
Quality[edit]
Cacao beans can be tested for their quality as a certain variety using DNA tests, especially by testing single-nucleotide polymorphisms that act as markers.[22]
See also[edit]
Food portal
Candy making
Chocolate bar
List of bean-to-bar chocolate manufacturers
List of desserts
References[edit]
Jump up ^ "Making Sense of % Cacao". CMA - Chocolate Manufacturers Association. 2 January 2008. Archived from the original on 2 January 2008. Retrieved 5 December 2011.
Jump up ^ The Oxford Companion to Sugar and Sweets (p. 524)
Jump up ^ "Wer hat's erfunden?" [Who invented it?]. mitteldeutschland.com. 9 December 2011. Archived from the original on 11 January 2012.
^ Jump up to: a b Moskin, Julia (13 February 2008). "Dark may be king, but milk chocolate makes a move". The New York Times. Retrieved 1 January 2016.
Jump up ^ "Directive 2000/36/EC of the European Parliament and of the Council of 23 June 2000 relating to cocoa and chocolate products intended for human consumption". Eur-lex.europa.eu. Retrieved 5 December 2011.
Jump up ^ Ascribed to Cadbury plc. (19 January 2010). "A history of Cadbury's sweet success". Times Online. London. Retrieved 30 May 2010.
Jump up ^ "Top 10 selling chocolate bars in the UK". Wales Online. Retrieved 29 December 2014
Jump up ^ "Chocolate as a Health Food?". Retrieved 3 March 2006.
Jump up ^ Cahalane, Claudia (30 March 2007). "A raw deal". The Guardian. London. Retrieved 5 December 2011.
Jump up ^ Mushet, C.; Sur La Table; Caruso, M. (2008). The Art and Soul of Baking. Andrews McMeel Publishing. pp. 39–40. ISBN 978-0-7407-7334-1.
Jump up ^ "Semisweet chocolate". Joy of Baking. iFood Media LLC. Retrieved 28 May 2015.
Jump up ^ "Title 21 – Food and Drugs, Chapter I, Sub chapter B – Food for Human Consumption, Part 163 – Cocoa Products". Title 21 – Food and Drugs. Food and Drug Administration Department of Health and Human Services. Retrieved 1 May 2007.
Jump up ^ "Types of Chocolate Products". Hershey.com. Archived from the original on 26 January 2009. Retrieved 1 May 2007.
Jump up ^ "To Our Stake older" (PDF). Archived from the original (PDF) on 2 December 2007. Retrieved 27 January 2008.
Jump up ^ (2007P-0085, Copy of 2007P-0085 Appendix C – search for cacao)
Jump up ^ "Responsibilities of the Agency: 11. (3) (a)". Canadian Food Inspection Agency Act. Department of Justice Canada. Retrieved 16 February 2012. The [Canadian Food Inspection] Agency is responsible for the enforcement of the Food and Drugs Act as it relates to food, as defined in section 2 of that Act
^ Jump up to: a b "Division 4: Cocoa and Chocolate Products". Food and Drug Regulations. Department of Justice Canada. Retrieved 16 February 2012.
Jump up ^ "Division 18: Sweetening Agents". Food and Drug Regulations. Department of Justice Canada. Retrieved 16 February 2012.
Jump up ^ "Guidance on the Cocoa and Chocolate Products Regulations 2003" (PDF). Retrieved 13 November 2010.
Jump up ^ "EU Agrees on Chocolate Definition Upsetting Major Cocoa Producers". www.thefreelibrary.com. Retrieved 18 September 2015.
Jump up ^ "Let the chocolate flow". Foodnavigator.com. 11 April 2001. Retrieved 5 December 2011.
Jump up ^ Nuwer, Rachel (16 January 2014). "A New Way to Find Out If Your Chocolate Is Legit". Smithsonian. Retrieved 29 May 2015.
[hide]
v
t
e
Chocolate
Overview
Outline
History (in Spain)
Theobroma
Theobroma
Theobroma cacao
Theobroma grandiflorum
Theobroma bicolor
Components
Cocoa bean
Cocoa butter
Cocoa solids
Chocolate liquor
Drugs
Anandamide
Caffeine
Phenethylamine
Theobromine
Theophylline
Types
Baking
Compound chocolate
Couverture chocolate
Dark chocolate
Milk chocolate
Modeling chocolate
Organic chocolate
White chocolate
Raw chocolate
Products
Chocolate bar
brands
Chocolate beverages
Chocolate biscuit
Chocolate brownie
Chocolate cake
Chocolate chip
Chocolate chip cookie
Chocolate coins
Chocolate crackles
Chocolate gravy
Chocolate ice cream
Chocolate liqueur
Chocolate milk
Chocolate pudding
Chocolate spread
Chocolate syrup
Chocolate truffle
Chocolate-covered foods
Cioccolato di Modica
Fudge
Ganache
Hot chocolate
Mint chocolate
Mocaccino
Mole sauce
Belgian chocolate
Swiss chocolate
Processes
Aerated chocolate
Broma process
Chocolate bloom
Chocolate temper meter
Conche
Dutch process
Enrober
Sugar crust
Industry
Big Chocolate
Children in cocoa production
Chocolaterie
Chocolatier
The Dark Side of Chocolate
European Cocoa and Chocolate Directive
Ghana Cocoa Board
Ghana production
Harkin–Engel Protocol
International Cocoa Organization
Ivory Coast production
Manufacturers (vertical)
Nigeria production
Philippine chocolate industry
World Cocoa Foundation
Other topics
Chocoholic
Chocolate fountain
Chocolate museums
Chocolatiers
Health effects
United States military chocolate
External links[edit]
Wikimedia Commons has media related to Types of chocolate.
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text:
Prime meridian
From Wikipedia, the free encyclopedia
Jump to: navigation, search
"Prime Meridian" redirects here. For the meridian often called the Prime Meridian, see Prime meridian (Greenwich).
0°
Prime Meridian
A prime meridian is a meridian (a line of longitude) in a geographical coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its antimeridian (the 180th meridian in a 360°-system) form a great circle. This great circle divides the sphere, e.g., the Earth, into two hemispheres. If one uses directions of East and West from a defined prime meridian, then they can be called Eastern Hemisphere and Western Hemisphere.
Gerardus Mercator in his Atlas Cosmographicae (1595) uses a prime meridian somewhere close to 25°W, passing just to the west of Santa Maria Island in the Atlantic. His 180th meridian runs along the Strait of Anián (Bering Strait)
A prime meridian is ultimately arbitrary, unlike an equator, which is determined by the axis of rotation—and various conventions have been used or advocated in different regions and throughout history.[1] The most widely used modern meridian is the IERS Reference Meridian. It is derived but deviates slightly from the Greenwich Meridian, which was selected as an international standard in 1884.
Contents
[hide]
1 History
2 List of prime meridians on Earth
3 International prime meridian
3.1 Prime meridian at Greenwich
3.2 IERS Reference Meridian
3.2.1 List of places
4 Prime meridian on other planetary bodies
5 See also
6 Notes
7 Citations
8 Works cited
9 External links
History[edit]
See also: History of longitude
Ptolemy's 1st projection, redrawn under Maximus Planudes around 1300, using a prime meridian east of Africa
The notion of longitude was developed by the Greek Eratosthenes (c. 276 BC – c. 195 BC) in Alexandria, and Hipparchus (c. 190 BC – c. 120 BC) in Rhodes, and applied to a large number of cities by the geographer Strabo (64/63 BC – c. 24 AD). But it was Ptolemy (c. AD 90 – c. AD 168) who first used a consistent meridian for a world map in his Geographia.
Ptolemy used as his basis the "Fortunate Isles", a group of islands in the Atlantic which are usually associated with the Canary Islands (13° to 18°W), although his maps correspond more closely to the Cape Verde islands (22° to 25° W). The main point is to be comfortably west of the western tip of Africa (17.5° W) as negative numbers were not yet in use. His prime meridian corresponds to 18° 40' west of Winchester (about 20°W) today.[2] At that time the chief method of determining longitude was by using the reported times of lunar eclipses in different countries.
Diogo Ribeiro's map of 1529, now in the Vatican library
Ptolemy's Geographia was first printed with maps at Bologna in 1477, and many early globes in the 16th century followed his lead. But there was still a hope that a "natural" basis for a prime meridian existed. Christopher Columbus reported (1493) that the compass pointed due north somewhere in mid-Atlantic, and this fact was used in the important Treaty of Tordesillas of 1494 which settled the territorial dispute between Spain and Portugal over newly discovered lands. The Tordesillas line was eventually settled at 370 leagues west of Cape Verde. This is shown in Diogo Ribeiro's 1529 map. São Miguel Island (25.5°W) in the Azores was still used for the same reason as late as 1594 by Christopher Saxton, although by then it had been shown that the zero magnetic deviation line did not follow a line of longitude.[3]
1571 Africa map by Abraham Ortelius, with Cabo Verde prime meridian
In 1541, Mercator produced his famous 41 cm terrestrial globe and drew his prime meridian precisely through Fuertaventura (14°1'W) in the Canaries. His later maps used the Azores, following the magnetic hypothesis. But by the time that Ortelius produced the first modern atlas in 1570, other islands such as Cape Verde were coming into use. In his atlas longitudes were counted from 0° to 360°, not 180°W to 180°E as is usual today. This practice was followed by navigators well into the 18th century.[4] In 1634, Cardinal Richelieu used the westernmost island of the Canaries, Ferro, 19° 55' west of Paris, as the choice of meridian. The geographer Delisle decided to round this off to 20°, so that it simply became the meridian of Paris disguised.[5]
In the early 18th century the battle was on to improve the determination of longitude at sea, leading to the development of the marine chronometer by John Harrison. But it was the development of accurate star charts, principally by the first British Astronomer Royal, John Flamsteed between 1680 and 1719 and disseminated by his successor Edmund Halley, that enabled navigators to use the lunar method of determining longitude more accurately using the octant developed by Thomas Godfrey and John Hadley.[6] Between 1765 and 1811, Nevil Maskelyne published 49 issues of the Nautical Almanac based on the meridian of the Royal Observatory, Greenwich. "Maskelyne's tables not only made the lunar method practicable, they also made the Greenwich meridian the universal reference point. Even the French translations of the Nautical Almanac retained Maskelyne's calculations from Greenwich—in spite of the fact that every other table in the Connaissance des Temps considered the Paris meridian as the prime." [7]
In 1884, at the International Meridian Conference in Washington, D.C., 22 countries voted to adopt the Greenwich[8] meridian as the prime meridian of the world. The French argued for a neutral line, mentioning the Azores and the Bering Strait, but eventually abstained and continued to use the Paris meridian until 1911.
List of prime meridians on Earth[edit]
Locality
Modern longitude
Meridian name
Comment
Bering Strait 168°30′ W
Bering Strait offered 1884 as possibility for a "neutral prime meridian" by Pierre Janssen at the International Meridian Conference [9]
Washington, D.C. 77°03′56.07″ W (1897) or 77°04′02.24″ W (NAD 27)[clarification needed] or 77°04′01.16″ W (NAD 83) New Naval Observatory meridian
Washington, D.C. 77°02′48.0″ W, 77°03′02.3″, 77°03′06.119″ W or 77°03′06.276″ W (both presumably NAD 27). If NAD27, the latter would be 77°03′05.194″ W (NAD 83) Old Naval Observatory meridian
Washington, D.C. 77°02′11.56299″ W (NAD 83),[10] 77°02′11.55811″ W (NAD 83),[11] 77°02′11.58325″ W (NAD 83)[12] (three different monuments originally intended to be on the White House meridian) White House meridian
Washington, D.C. 77°00′32.6″ W (NAD 83) Capitol meridian
Philadelphia 75° 10′ 12″ W [13][14]
Rio de Janeiro 43° 10′ 19″ W [15]
Fortunate Isles / Azores 25° 40′ 32″ W Used until the Middle Ages, proposed as one possible neutral meridian by Pierre Janssen at the International Meridian Conference[16]
El Hierro (Ferro),
Canary Islands 18° 03′ W,
later redefined as
17° 39′ 46″ W Ferro meridian [17]
Tenerife 16° 38' 22" W Tenerife meridian Rose to prominence with Dutch cartographers and navigators after they abandoned the idea of a magnetic meridian[18]
Cadiz 6° 17' 40" W San Fernando meridian [19]
Lisbon 9° 07′ 54.862″ W [20]
Madrid 3° 41′ 16.58″ W [20]
Greenwich 0° 00′ 05.3101″ W Greenwich meridian Airy Meridian[21]
Greenwich 0° 00′ 05.33″ W United Kingdom Ordnance Survey Zero Meridian Bradley Meridian[21]
Greenwich 0° 00′ 00.00″ IERS Reference Meridian
Paris 2° 20′ 14.025″ E Paris meridian
Brussels 4° 22′ 4.71″ E [20]
Antwerp 4° 24′ E Antwerp meridian [citation needed]
Amsterdam 4° 53′ E through the Westerkerk in Amsterdam; used to define the legal time in the Netherlands from 1909 to 1937[22]
Bern 7° 26′ 22.5″ E [citation needed]
Pisa 10° 24′ E [13]
Oslo (Kristiania) 10° 43′ 22.5″ E [13][14]
Florence 11°15′ E Florence meridian used in the Peters projection, antipode of a line running through the Bering Strait
Rome 12° 27′ 08.4″ E meridian of Monte Mario Used in Roma 40 Datum [23]
Copenhagen 12° 34′ 32.25″ E Rundetårn[24]
Naples 14° 15′ E [16]
Bratislava 17° 06′ 03″ E Meridianus Posoniensis Used by Sámuel Mikoviny
Stockholm 18° 03′ 29.8″ E at the Stockholm Observatory[20]
Kraków 19° 57′ 21.43″ E Kraków meridian at the Old Kraków Observatory at the Śniadecki' College; mentioned also in Nicolaus Copernicus's work On the Revolutions of the Heavenly Spheres.
Warsaw 21° 00′ 42″ E Warsaw meridian [20]
Oradea 21° 55′ 16″ E [25] Between 1464 and 1667, a prime meridian was set in the Fortress of Oradea (Varadinum at the time) by Georg von Peuerbach.[26]
Alexandria 29° 53′ E [27]
Saint Petersburg 30° 19′ 42.09″ E Pulkovo meridian
Great Pyramid of Giza 31° 08′ 03.69″ E 1884 [28]
Jerusalem 35° 13′ 47.1″ E [14]
Mecca 39° 49′ 34″ E see also Mecca Time [29]
Ujjain 75° 47′ E Used from 4th century CE Indian astronomy and calendars(see also Time in India).[30]
Kyoto 136° 14′ E Used in 18th and 19th (officially 1779–1871) century Japanese maps. Exact place unknown, but in "Kairekisyo" in Nishigekkoutyou-town in Kyoto, then the capital.[citation needed]
~ 180 Opposite of Greenwich, proposed 13 October 1884 on the International Meridian Conference by Sandford Fleming [16]
International prime meridian[edit]
In October 1884 the Greenwich Meridian was selected by delegates (forty-one delegates representing twenty-five nations) to the International Meridian Conference held in Washington, D.C., United States to be the common zero of longitude and standard of time reckoning throughout the world.[31][note 1] The modern prime meridian, the IERS Reference Meridian, is placed very near this meridian and is the prime meridian that currently has the widest use.
Prime meridian at Greenwich[edit]
Markings of the prime meridian at the Royal Observatory, Greenwich.
Main article: Prime meridian (Greenwich)
The modern prime meridian, based at the Royal Observatory, Greenwich, was established by Sir George Airy in 1851.[33]
The position of the Greenwich Meridian has been defined by the location of the Airy Transit Circle ever since the first observation was taken with it by Sir George Airy in 1851.[33] Prior to that, it was defined by a succession of earlier transit instruments, the first of which was acquired by the second Astronomer Royal, Edmond Halley in 1721. It was set up in the extreme north-west corner of the Observatory between Flamsteed House and the Western Summer House. This spot, now subsumed into Flamsteed House, is roughly 43 metres to the west of the Airy Transit Circle, a distance equivalent to roughly 0.15 seconds of time.[21] It was Airy's transit circle that was adopted in principle (with French delegates, who pressed for adoption of the Paris meridian abstaining) as the Prime Meridian of the world at the 1884 International Meridian Conference.[34][35]
All of these Greenwich meridians were located via an astronomic observation from the surface of the Earth, oriented via a plumb line along the direction of gravity at the surface. This astronomic Greenwich meridian was disseminated around the world, first via the lunar distance method, then by chronometers carried on ships, then via telegraph lines carried by submarine communications cables, then via radio time signals. One remote longitude ultimately based on the Greenwich meridian using these methods was that of the North American Datum 1927 or NAD27, an ellipsoid whose surface best matches mean sea level under the United States.
IERS Reference Meridian[edit]
Main article: IERS Reference Meridian
Satellites changed the reference from the surface of the Earth to its centre of mass around which all satellites orbit regardless of surface irregularities. The requirement that satellite-based geodetic reference systems be centred on the centre of mass of the earth caused the modern prime meridian to be 5.3" east of the astronomic Greenwich prime meridian through the Airy Transit Circle. At the latitude of Greenwich, this amounts to 102 metres.[36] This was officially accepted by the Bureau International de l'Heure (BIH) in 1984 via its BTS84 (BIH Terrestrial System) that later became WGS84 (World Geodetic System 1984) and the various ITRFs (International Terrestrial Reference Systems).
Due to the movement of Earth's tectonic plates, the line of 0° longitude along the surface of the Earth has slowly moved toward the west from this shifted position by a few centimetres; that is, towards the Airy Transit Circle (or the Airy Transit Circle has moved toward the east, depending on your point of view) since 1984 (or the 1960s). With the introduction of satellite technology, it became possible to create a more accurate and detailed global map. With these advances there also arose the necessity to define a reference meridian that, whilst being derived from the Airy Transit Circle, would also take into account the effects of plate movement and variations in the way that the Earth was spinning.[37] As a result, the International Reference Meridian was established and is commonly used to denote Earth's prime meridian (0° longitude) by the International Earth Rotation and Reference Systems Service, which defines and maintains the link between longitude and time. Based on observations to satellites and celestial compact radio sources (quasars) from various coordinated stations around the globe, Airy's transit circle drifts northeast about 2.5 centimetres per year relative to this Earth-centred 0° longitude. Circa 1999 the international reference meridian (IRM) passed 5.31 arcseconds east of Airy's meridian or 102.5 metres (336.3 feet) at the latitude of the Royal Observatory, Greenwich, London.[38][39][40][41] It is also the reference meridian of the Global Positioning System operated by the United States Department of Defense, and of WGS84 and its two formal versions, the ideal International Terrestrial Reference System (ITRS) and its realization, the International Terrestrial Reference Frame (ITRF).[38][39][40] A current convention on the Earth uses the opposite of the IRM as the basis for the International Date Line.
List of places[edit]
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Place data as RDF
On Earth, starting at the North Pole and heading south to the South Pole, the IERS Reference Meridian (as of 2016) passes through:
Co-ordinates
(approximate)
Country, territory or sea
Notes
90°0′N 0°0′E / 90.000°N 0.000°E / 90.000; 0.000 (North Pole)
Arctic Ocean
81°39′N 0°0′E / 81.650°N 0.000°E / 81.650; 0.000 (Greenland Sea)
Greenland Sea
72°53′N 0°0′E / 72.883°N 0.000°E / 72.883; 0.000 (Norwegian Sea)
Norwegian Sea
61°0′N 0°0′E / 61.000°N 0.000°E / 61.000; 0.000 (North Sea)
North Sea
53°45′N 0°0′E / 53.750°N 0.000°E / 53.750; 0.000 (United Kingdom)
United Kingdom
From Tunstall in East Riding to Peacehaven, passing through Greenwich
50°47′N 0°0′E / 50.783°N 0.000°E / 50.783; 0.000 (English Channel)
English Channel
49°19′N 0°0′E / 49.317°N 0.000°E / 49.317; 0.000 (France)
France
From Villers-sur-Mer to Gavarnie
42°41′N 0°0′E / 42.683°N 0.000°E / 42.683; 0.000 (Spain)
Spain
From Cilindro de Marboré to Castellón de la Plana
39°56′N 0°0′E / 39.933°N 0.000°E / 39.933; 0.000 (Mediterranean Sea)
Mediterranean Sea
Gulf of Valencia
38°52′N 0°0′E / 38.867°N 0.000°E / 38.867; 0.000 (Spain)
Spain
From El Verger to Calpe
38°38′N 0°0′E / 38.633°N 0.000°E / 38.633; 0.000 (Mediterranean Sea)
Mediterranean Sea
35°50′N 0°0′E / 35.833°N 0.000°E / 35.833; 0.000 (Algeria)
Algeria
From Stidia to Algeria-Mali border near Bordj Mokhtar
21°50′N 0°0′E / 21.833°N 0.000°E / 21.833; 0.000 (Mali)
Mali
14°59′N 0°0′E / 14.983°N 0.000°E / 14.983; 0.000 (Burkina Faso)
Burkina Faso
11°6′N 0°0′E / 11.100°N 0.000°E / 11.100; 0.000 (Togo)
Togo
For about 600 m
11°6′N 0°0′E / 11.100°N 0.000°E / 11.100; 0.000 (Ghana)
Ghana
For about 16 km
10°57′N 0°0′E / 10.950°N 0.000°E / 10.950; 0.000 (Togo)
Togo
For about 39 km
10°36′N 0°0′E / 10.600°N 0.000°E / 10.600; 0.000 (Ghana)
Ghana
From the Togo-Ghana border near Bunkpurugu to Tema
Passing through Lake Volta at 7°48′N 0°0′E / 7.800°N 0.000°E / 7.800; 0.000 (Lake Volta)
5°37′N 0°0′E / 5.617°N 0.000°E / 5.617; 0.000 (Atlantic Ocean)
Atlantic Ocean
Passing through the Equator at 0°0′N 0°0′E / 0.000°N 0.000°E / 0.000; 0.000 (Equator) ("Null Island")
60°0′S 0°0′E / 60.000°S 0.000°E / -60.000; 0.000 (Southern Ocean)
Southern Ocean
68°54′S 0°0′E / 68.900°S 0.000°E / -68.900; 0.000 (Antarctica)
Antarctica
Queen Maud Land, claimed by Norway
Prime meridian on other planetary bodies[edit]
See also: Longitude (planets)
"Prime meridian (planets)" redirects here. It is not to be confused with Central meridian (planets).
As on the Earth, prime meridians must be arbitrarily defined. Often a landmark such as a crater is used; other times a prime meridian is defined by reference to another celestial object, or by magnetic fields. The prime meridians of the following planetographic systems have been defined:
Two different heliographic coordinate systems are used on the Sun. The first is the Carrington heliographic coordinate system. In this system, the prime meridian passes through the center of the solar disk as seen from the Earth on 9 November 1853, which is when Richard Christopher Carrington started his observations of sunspots.[42] The second is the Stonyhurst heliographic coordinates system.
The prime meridian of Mercury is defined to be 20° east of the crater Hun Kal.[43]
The prime meridian of Venus passes through the central peak in the crater Ariadne.[44]
The prime meridian of the Moon lies directly in the middle of the face of the moon visible from Earth and passes near the crater Bruce.
The prime meridian of Mars is defined by the crater Airy-0.
Jupiter has several coordinate systems because its cloud tops—the only part of the planet visible from space—rotate at different rates depending on latitude.[45] It is unknown whether Jupiter has any internal solid surface that would enable a more Earth-like coordinate system. System I and System II coordinates are based on atmospheric rotation, and System III coordinates use Jupiter's magnetic field.
Titan, like the Earth's moon, always has the same face towards Saturn, and so the middle of that face is 0 longitude.
Pluto's prime meridian is defined as the center of the face that is always pointed towards Charon, its largest moon, as the two are tidally locked towards each other.
See also[edit]
Geography portal
1st meridian east
1st meridian west
Notes[edit]
Jump up ^ Voting took place on 13 October and the resolutions were adopted on 22 October 1884.[32]
Citations[edit]
Jump up ^ Prime Meridian, geog.port.ac.uk
Jump up ^ Norgate & Norgate 2006
Jump up ^ Hooker 2006
Jump up ^ e.g. Jacob Roggeveen in 1722 reported the longitude of Easter Island as 268° 45' (starting from Fuertaventura) in the Extract from the Official log of Jacob Roggeveen reproduced in Bolton Glanville Corney, ed. (1908), The voyage of Don Felipe Gonzalez to Easter Island in 1770-1, Hakluyt Society, p. 3, retrieved 13 January 2013
Jump up ^ Speech by Pierre Janssen, director of the Paris observatory, at the first session of the Meridian Conference.
Jump up ^ Sobel & Andrewes 1998, pp. 110–115
Jump up ^ Sobel & Andrewes 1998, pp. 197–199
Jump up ^ "The Prime Meridian at Greenwich". Royal Museums Greenwich. n.d. Retrieved 28 March 2016.
Jump up ^ International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884. Project Gutenberg
Jump up ^ NGS 2016, PID: HV1847.
Jump up ^ NGS 2016, PID: HV1846.
Jump up ^ NGS 2016, PID: AH7372.
^ Jump up to: a b c Hooker (2006), introduction.
^ Jump up to: a b c Oct. 13, 1884: Greenwich Resolves Subprime Meridian Crisis, WIRED, 13 October 2010.
Jump up ^ Atlas do Brazil, 1909, by Barão Homem de Mello e Francisco Homem de Mello, published in Rio de Janeiro by F. Briguiet & Cia.
^ Jump up to: a b c "The Project Gutenberg eBook of International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day". Gutenberg.org. 12 February 2006. Retrieved 28 March 2016.
Jump up ^ Ancient, used in Ptolemy's Geographia. Later redefined 17° 39′ 46″ W of Greenwich to be exactly 20° W of Paris. French "submarin" at Washington 1884.
Jump up ^ A.R.T. Jonkers; Parallel meridians: Diffusion and change in early modern oceanic reckoning, in Noord-Zuid in Oostindisch perspectief, The Hague, 2005, p. 7. Retrieved 2 February 2015.
Jump up ^ , [1], in El País, 2016, retrieved 23 December 2016.
^ Jump up to: a b c d e Bartky, Ian R. (2007), One Time Fits All: The Campaigns for Global Uniformity, p. 98, retrieved through GoogleBooks, 6 May 2014.
^ Jump up to: a b c Dolan 2013a.
Jump up ^ (in Dutch)Eenheid van tijd in Nederland (Unity of time in the Netherlands), Utrecht University website, retrieved 28 August 2013.
Jump up ^ Grids & Datums – Italian Republic, asprs.org, Retrieved 10 December 2013.
Jump up ^ meridian, article from Den Store Danske Encyklopædi
Jump up ^ Oradea, Tourism office website, retrieved 3 February 2015.
Jump up ^ "Romanian astronaut makrsk 10th anniversary of Prime Meridian Astronomy Club". NineO'Clock.ro. 2015. Retrieved 26 June 2017.
Jump up ^ The meridian of Ptolemy's Almagest.
Jump up ^ Wilcomb E. Washburn, "The Canary Islands and the Question of the Prime Meridian: The Search for Precision in the Measurement of the Earth"
Jump up ^ Maimonides, Hilchot Kiddush Hachodesh 11:17, calls this point אמצע היישוב, "the middle of the habitation", i.e. the habitable hemisphere. Evidently this was a convention accepted by Arab geographers of his day.
Jump up ^ Burgess 1860
Jump up ^ "International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884. Protocols of the proceedings". Project Gutenberg. 1884. Retrieved 30 November 2012.
Jump up ^ Howse 1997, pp. 12, 137
^ Jump up to: a b Greenwich Observatory ... the story of Britain's oldest scientific institution, the Royal Observatory at Greenwich and Herstmonceux, 1675–1975 p.10. Taylor & Francis, 1975
Jump up ^ McCarthy, Dennis; Seidelmann, P. Kenneth (2009). TIME from Earth Rotation to Atomic Physics. Weinheim: Wiley-VCH. pp. 244–5.
Jump up ^ ROG Learning Team (23 August 2002). "The Prime Meridian at Greenwich". Royal Museums Greenwich. Royal Museums Greenwich. Retrieved 14 June 2012.
Jump up ^ Malys, Stephen; Seago, John H.; Palvis, Nikolaos K.; Seidelmann, P. Kenneth; Kaplan, George H. (1 August 2015). "Why the Greenwich meridian moved". Journal of Geodesy. 89 (12): 1263. Bibcode:2015JGeod..89.1263M. doi:10.1007/s00190-015-0844-y.
Jump up ^ Dolan 2013b.
^ Jump up to: a b History of the Prime Meridian -Past and Present
^ Jump up to: a b IRM on grounds of Royal Observatory from Google Earth Accessed 30 March 2012
^ Jump up to: a b The astronomic latitude of the Royal Observatory is 51°28'38"N whereas its latitude on the European Terrestrial Reference Frame (1989) datum is 51°28'40.1247"N.
Jump up ^ Guinot, B., 2011. Solar time, legal time, time in use. Metrologica 48, S181–S185.
Jump up ^ "Carrington heliographic coordinates".
Jump up ^ Archinal, B. A.; A’Hearn, M. F.; Bowell, E.; Conrad, A.; Consolmagno, G. J.; Courtin, R.; Fukushima, T.; Hestroffer, D.; Hilton, J. L.; Krasinsky, G. A.; Neumann, G.; Oberst, J.; Seidelmann, P. K.; Stooke, P.; Tholen, D. J.; Thomas, P. C.; Williams, I. P. (23 October 2010). "Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009" (PDF). Celestial Mechanics and Dynamical Astronomy. 109 (2): 15. Bibcode:2011CeMDA.109..101A. doi:10.1007/s10569-010-9320-4.
Jump up ^ "USGS Astrogeology: Rotation and pole position for the Sun and planets (IAU WGCCRE)". Retrieved 22 October 2009.
Jump up ^ "Planetographic Coordinates". Retrieved 24 May 2017.
Works cited[edit]
Burgess, Ebenezer (1860), "Translation of the Surya-Siddhanta", Journal of the American Oriental Society (e book), 6, Google (published c. 2013), p. 185
Dolan, Graham (2013a). "The Greenwich Meridian before the Airy Transit Circle". The Greenwich Meridian.
Dolan, Graham (2013b). "WGS84 and the Greenwich Meridian". The Greenwich Meridian.
Hooker, Brian (2006), A multitude of prime meridians, retrieved 13 January 2013
Howse, Derek (1997), Greenwich Time and the Longitude, Phillip Wilson, ISBN 0-85667-468-0, ASIN 0948065265
Norgate, Jean; Norgate, Martin (2006), Prime meridian, retrieved 13 January 2013
NGS datasheet station name form, National Geodetic Survey, 2016, retrieved 11 December 2016
Sobel, Dava; Andrewes, William J. H. (1998), The Illustrated Longitude, Fourth Estate, London
External links[edit]
Wikimedia Commons has media related to Prime meridian.
"Where the Earth's surface begins—and ends", Popular Mechanics, December 1930
scanned TIFFs of the conference proceedings
Prime meridians in use in the 1880s, by country
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Nitrification
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Not to be confused with Nitration.
Nitrogen cycle
Nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate.[1] The transformation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil. Nitrification is an aerobic process performed by small groups of autotrophic bacteria and archaea. This process was discovered by the Russian microbiologist Sergei Winogradsky.
Contents
[hide]
1 Microbiology and ecology
2 Chemistry and Enzymology
3 Nitrification in the marine environment
4 Soil Conditions controlling nitrification rates
5 Inhibitors of nitrification
6 Methane inhibition
7 Environmental concerns
8 See also
9 References
10 External links
Microbiology and ecology[edit]
The oxidation of ammonia into nitrite is performed by two groups of organisms, ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA[2]).[3] AOB can be found among the β-proteobacteria and gammaproteobacteria.[4] Currently, two AOA, Nitrosopumilus maritimus and Nitrososphaera viennensis, have been isolated and described.[5] In soils the most studied AOB belong to the genera Nitrosomonas and Nitrosococcus. Although in soils ammonia oxidation occurs by both AOB and AOA, AOA dominate in both soils and marine environments,[2][6][7] suggesting that Thaumarchaeota may be greater contributors to ammonia oxidation in these environments.[2]
The second step (oxidation of nitrite into nitrate) is done (mainly) by bacteria of the genus Nitrobacter and Nitrospira. Both steps are producing energy to be coupled to ATP synthesis. Nitrifying organisms are chemoautotrophs, and use carbon dioxide as their carbon source for growth. Some AOB possess the enzyme, urease, which catalyzes the conversion of the urea molecule to two ammonia molecules and one carbon dioxide molecule. Nitrosomonas europaea, as well as populations of soil-dwelling AOB, have been shown to assimilate the carbon dioxide released by the reaction to make biomass via the Calvin Cycle, and harvest energy by oxidizing ammonia (the other product of urease) to nitrite. This feature may explain enhanced growth of AOB in the presence of urea in acidic environments.[8]
In most environments, organisms are present that will complete both steps of the process, yielding nitrate as the final product. However, it is possible to design systems in which nitrite is formed (the Sharon process).
Nitrification is important in agricultural systems, where fertilizer is often applied as ammonia. Conversion of this ammonia to nitrate increases nitrogen leaching because nitrate is more water-soluble than ammonia.
Nitrification also plays an important role in the removal of nitrogen from municipal wastewater. The conventional removal is nitrification, followed by denitrification. The cost of this process resides mainly in aeration (bringing oxygen in the reactor) and the addition of an external carbon source (e.g., methanol) for the denitrification.
Nitrification can also occur in drinking water. In distribution systems where chloramines are used as the secondary disinfectant, the presence of free ammonia can act as a substrate for ammonia-oxidizing microorganisms. The associated reactions can lead to the depletion of the disinfectant residual in the system.[9] The addition of chlorite ion to chloramine-treated water has been shown to control nitrification.[10][11]
Together with ammonification, nitrification forms a mineralization process that refers to the complete decomposition of organic material, with the release of available nitrogen compounds. This replenishes the nitrogen cycle.
Chemistry and Enzymology[edit]
Nitrification is a process of nitrogen compound oxidation (effectively, loss of electrons from the nitrogen atom to the oxygen atoms), and is catalyzed step-wise by a series of enzymes.
2 NH4+ + 3 O2 → 2 NO2− + 2 H2O + 4 H+ (Nitrosomonas, Comammox) 2 NO2− + O2 → 2 NO3− (Nitrobacter, Nitrospira, Comammox)

-OR-
NH3 + O2 → NO2− + 3H+ + 2e− NO2− + H2O → NO3− + 2H+ + 2e−

In Nitrosomonas europaea, the first step of oxidation (ammonia to hydroxylamine) is carried out by the enzyme ammonia monooxygenase (AMO).
NH 3 + O 2 + 2 H + ⟶ NH 2 OH + H 2 O {\displaystyle {\ce {NH3 + O2 + 2H+ -> NH2OH + H2O}}}
The second step (hydroxylamine to nitrite) is carried out step-wise by two different enzymes. Hydroxylamine oxidoreductase (HAO), converts hydroxylamine to nitric oxide.[12]
NH 2 OH ⟶ NO + 3 H + + 3 e − {\displaystyle {\ce {NH2OH -> NO + 3H+ + 3e-}}}
Another as-of-yet unknown enzyme that converts nitric oxide to nitrite.
The third step (nitrite to nitrate) is completed in a different organism.
nitrite + acceptor ↽ − − ⇀ nitrate + reduced acceptor {\displaystyle {\ce {{nitrite}+acceptor<=>{nitrate}+reduced\ acceptor}}}
Nitrification in the marine environment[edit]
In the marine environment, nitrogen is often the limiting nutrient, so the nitrogen cycle in the ocean is of particular interest.[13][14] The nitrification step of the cycle is of particular interest in the ocean because it creates nitrate, the primary form of nitrogen responsible for "new" production. Furthermore, as the ocean becomes enriched in anthropogenic CO2, the resulting decrease in pH could lead to decreasing rates of nitrification. Nitrification could potentially become a "bottleneck" in the nitrogen cycle.[15]
Nitrification, as stated above, is formally a two-step process; in the first step ammonia is oxidized to nitrite, and in the second step nitrite is oxidized to nitrate. Different microbes are responsible for each step in the marine environment. Several groups of ammonia-oxidizing bacteria (AOB) are known in the marine environment, including Nitrosomonas, Nitrospira, and Nitrosococcus. All contain the functional gene ammonia monooxygenase (AMO) which, as its name implies, is responsible for the oxidation of ammonia.[2][14] More recent metagenomic studies have revealed that some Thaumarchaeota (formerly Crenarchaeota) possess AMO. Thaumarchaeotes are abundant in the ocean and some species have a 200 times greater affinity for ammonia than AOB, leading researchers to challenge the previous belief that AOB are primarily responsible for nitrification in the ocean.[16] Furthermore, though nitrification is classically thought to be vertically separated from primary production because the oxidation of nitrogen by bacteria is inhibited by light, nitrification by AOA does not appear to be light inhibited, meaning that nitrification is occurring throughout the water column, challenging the classical definitions of "new" and "recycled" production.[16]
In the second step, nitrite is oxidized to nitrate. In the oceans, this step is not as well understood as the first, but the bacteria Nitrospina and Nitrobacter are known to carry out this step in the sea.[16]
Soil Conditions controlling nitrification rates[edit]
• Substrate availability (presence of NH4+)
• Aeration (availability of O2)
• Well-drained soils with 60% soil moisture
• pH (near neutral)
• Temperature (best 20-30°C) => Nitrification is seasonal, affected by land use practices
Inhibitors of nitrification[edit]
Nitrification inhibitors are chemical compounds that slow the nitrification of ammonia, ammonium-containing, or urea-containing fertilizers, which are applied to soil as fertilizers. These inhibitors can help reduce losses of nitrogen in soil that would otherwise be used by crops. Nitrification inhibitors are used widely, being added to approximately 50% of the fall-applied anhydrous ammonia in states in the U.S., like Illinois.[17] They are usually effective in increasing recovery of nitrogen fertilizer in row crops, but the level of effectiveness depends on external conditions and their benefits are most likely to be seen at less than optimal nitrogen rates.[18]
The environmental concerns of nitrification also contribute to interest in the use of nitrification inhibitors: the primary product, nitrate, leaches into groundwater, producing acute toxicity in multiple species of wildlife and contributing to the eutrophication of standing water. Some inhibitors of nitrification also inhibit the production of methane, a greenhouse gas.
The inhibition of the nitrification process is primarily facilitated by the selection and inhibition/destruction of the bacteria that oxidize ammonia compounds. A multitude of compounds that inhibit nitrification, which can be divided into the following areas: the active site of ammonia monooxygenase (AMO), mechanistic inhibitors, and the process of N-heterocyclic compounds. The process for the latter of the three is not yet widely understood, but is prominent. The presence of AMO has been confirmed on many substrates that are nitrogen inhibitors such as dicyandiamide, ammonium thiosulfate, and nitrapyrin.
The conversion of ammonia to hydroxylamine is the first step in nitrification, where AH2 represents a range of potential electron donors.
NH3 + AH2 + O2 → NH2OH + A + H2O
This reaction is catalyzed by AMO. Inhibitors of this reaction bind to the active site on AMO and prevent or delay the process. The process of oxidation of ammonia by AMO is regarded with importance due to the fact that other processes require the co-oxidation of NH3 for a supply of reducing equivalents. This is usually supplied by the compound hydroxylamine oxidoreductase (HAO) which catalyzes the reaction:
NH2OH + H2O → NO2− + 5 H+ + 4 e−
The mechanism of inhibition is complicated by this requirement. Kinetic analysis of the inhibition of NH3 oxidation has shown that the substrates of AMO have shown kinetics ranging from competitive to noncompetitive. The binding and oxidation can occur on two different locations on AMO: in competitive substrates, binding and oxidation occurs at the NH3 site, while in noncompetitive substrates it occurs at another site.
Mechanism based inhibitors can be defined as compounds that interrupt the normal reaction catalyzed by an enzyme. This method occurs by the inactivation of the enzyme via covalent modification of the product, which ultimately inhibits nitrification. Through the process, AMO is deactivated and one or more proteins is covalently bonded to the final product. This is found to be most prominent in a broad range of sulfur or acetylenic compounds.
Sulfur-containing compounds, including ammonium thiosulfate (a popular inhibitor) are found to operate by producing volatile compounds with strong inhibitory effects such as carbon disulfide and thiourea.
In particular, thiophosphoryl triamide has been a notable addition where it has the dual purpose of inhibiting both the production of urease and nitrification.[19] In a study of inhibitory effects of oxidation by the bacteria Nitrosomonas europaea, the use of thioethers resulted in the oxidation of these compounds to sulfoxides, where the S atom is the primary site of oxidation by AMO. This is most strongly correlated to the field of competitive inhibition.
Examples of N-heterocyclic molecules.
N-heterocyclic compounds are also highly effective nitrification inhibitors and are often classified by their ring structure. The mode of action for these compounds is not well understood: while nitrapyrin, a widely used inhibitor and substrate of AMO, is a weak mechanism-based inhibitor of said enzyme, the effects of said mechanism are unable to correlate directly with the compound’s ability to inhibit nitrification. It is suggested that nitrapyrin acts against the monooxygenase enzyme within the bacteria, preventing growth and CH4/NH4 oxidation.[20] Compounds containing two or three adjacent ring N atoms (pyridazine, pyrazole, indazole) tend to have a significantly higher inhibition effect than compounds containing non-adjacent N atoms or singular ring N atoms (pyridine, pyrrole).[21] This suggests that the presence of ring N atoms is directly correlated with the inhibition effect of this class of compounds.
Methane inhibition[edit]
Some enzymatic nitrification inhibitors, such as urease, can also inhibit the production of methane in methanotrophic bacteria. AMO shows similar kinetic turnover rates to methane monooxygenase (MMO) found in methanotrophs, indicating that MMO is a similar catalyst to AMO for the purpose of methane oxidation. Furthermore, methanotrophic bacteria share many similarities to NH3 oxidizers such as Nitrosomonas.[22] The inhibitor profile of particulate forms of MMO (pMMO) shows similarity to the profile of AMO, leading to similarity in properties between MMO in methanotrophs and AMO in autotrophs.
Environmental concerns[edit]
Nitrification inhibitors are also of interest from an environmental standpoint because of the production of nitrates and nitrous oxide from the process of nitrification. Nitrous oxide (N2O), although its atmospheric concentration is much lower than that of CO2, has a global warming potential of about 300 times greater than carbon dioxide and contributes 6% of planetary warming due to greenhouse gases. This compound is also notable for catalyzing the breakup of ozone in the stratosphere.[23] Nitrates, a toxic compound for wildlife and livestock and a product of nitrification, are also of concern.
Soil, consisting of polyanionic clays and silicates, generally has a net anionic charge. Consequently, ammonium (NH4+) binds tightly to the soil but nitrate ions (NO3−) do not. Because nitrate is more mobile, it leaches into groundwater supplies through agricultural runoff. Wildlife such as amphibians, freshwater fish, and insects are sensitive to nitrate levels, and have been known to cause death and developmental anomalies in affected species.[24] In addition, because they easily leach into groundwater, contributing to eutrophication, a process in which large algal blooms reduce oxygen levels in bodies of water and lead to death in oxygen-consuming creatures due to anoxia. Nitrification is also thought to contribute to the formation of photochemical smog, ground level ozone, acid rain, changes in species diversity, and other undesirable processes. In addition, nitrification inhibitors have also been shown to suppress the oxidation of methane (CH4), a potent greenhouse gas, to CO2. Both nitrapyrin and acetylene are shown to be especially strong suppressors of both processes, although the modes of action distinguishing them are unclear.
See also[edit]
f-ratio
Haber process
Nitrifying bacteria
Nitrogen fixation
Simultaneous nitrification-denitrification
Comammox
References[edit]
Jump up ^ Nitrification Network. "Nitrification primer". nitrificationnetwork.org. Oregon State University. Retrieved 21 August 2014.
^ Jump up to: a b c d Hatzenpichler R. (2012) Diversity, physiology and niche differentiation of ammonia-oxidizing archaea. Appl Environ Microbiol 78: 7501-7510
Jump up ^ Treusch, A.H., Leininger, S., Kletzin, A., Schuster, S.C., Klenk, H.P., and Schleper, C. (2005) Novel genes for nitrite reductase and Amo-related proteins indicate a role of uncultivated mesophilic crenarchaeota in nitrogen cycling. Environ Microbiol 7: 1985–1995
Jump up ^ Purkhold, U., Pommerening-Roser, A., Juretschko, S.,Schmid, M.C., Koops, H.-P., and Wagner, M. (2000) Phylogeny of all recognized species of ammonia oxidizers based on comparative 16S rRNA and amoA sequence analysis: implications for molecular diversity surveys. Appl Environ Microbiol 66: 5368–5382
Jump up ^ Martens-Habbena, W., Berube, P. M., Urakawa, H., de la Torre, J. R., Stahl, D. A. 2009. Ammonia oxidation kinetics determine niche separation of nitrifying Archaea and Bacteria. Nature 461: 976-981.
Jump up ^ Wuchter, C., Abbas, B., Coolen, M.J.L., Herfort, L., van Bleijswijk, J., Timmers, P., et al. (2006) Archaeal nitrification in the ocean. Proc Natl Acad Sci USA 103: 12317–12322.
Jump up ^ Leininger, S.; Urich, T.; Schloter, M.; Schwark, L.; Qi, J.; Nicol, G. W.; Prosser, J. I.; Schuster, S. C.; Schleper, C. (2006). "Archaea predominate among ammonia-oxidizing prokaryotes in soils" (PDF). Nature. 442 (7104): 806–809. doi:10.1038/nature04983. PMID 16915287.
Jump up ^ Marsh, K. L., G. K. Sims, and R. L. Mulvaney. 2005. Availability of urea to autotrophic ammonia-oxidizing bacteria as related to the fate of 14C- and 15N-labeled urea added to soil. Biol. Fert. Soil. 42:137-145.
Jump up ^ Zhang, Y, Love, N, & Edwards, M (2009), "Nitrification in Drinking Water Systems", Critical Reviews in Environmental Science and Technology, 39(3):153-208, doi:10.1080/10643380701631739.
Jump up ^ McGuire, M.J., Lieu, N.I. and Pearthree, M.S. (1999). “Using Chlorite Ion to Control Nitrification,” Journal American Water Works Association. 91:10 (October) 52-61.
Jump up ^ McGuire, M.J., Wu, X., Blute, N.K., Askenaizer, D., and Qin, G. (2009). “Prevention of nitrification using chlorite ion: Results of a demonstration project in Glendale, Calif.,” Journal American Water Works Association. 101:10 (October) 47-59.
Jump up ^ Caranto, Jonathan D.; Lancaster, Kyle M. (2017-08-01). "Nitric oxide is an obligate bacterial nitrification intermediate produced by hydroxylamine oxidoreductase". Proceedings of the National Academy of Sciences. 114 (31): 8217–8222. doi:10.1073/pnas.1704504114. ISSN 0027-8424. PMID 28716929.
Jump up ^ Zehr, J. P. and R. M. Kudela. 2011. Nitrogen cycle of the open ocean: from genes to ecosystems. Annu. Rev. Mar Sci. 3:197-225.
^ Jump up to: a b Nitrification and Denitrification: Probing the Nitrogen Cycle in Aquatic Environments B. B. Ward Microbial Ecology Vol. 32, No. 3 (1996), pp. 247-261
Jump up ^ Hutchins, D. A., Mulholland, M. R., Fu, F. (2009). Nutrient cycles and marine microbes in a CO2-enriched ocean. Oceanography. Vol. 22, pp. 128-145.
^ Jump up to: a b c Zehr, J. P. and Kudela R. M.. 2011. Nitrogen cycle of the open ocean: from genes to ecosystems. Annu. Rev. Mar Sci. 3:197-225.
Jump up ^ Czapar, G; Payne, J; Tate, J. An Educational Program on the Proper Training of Fall-applied Nitrogen Fertilizer. Crop Management, 2007, 6(1). doi:10.1094/CM-2007-0510-01-RS
Jump up ^ Ferguson, R; Lark, R; Slater, G. Approaches to management zone definition for use of nitrification inhibitors. Soil Sci. Soc. Am. J., 2003, 67, p. 937-947. doi:10.2136/sssaj2003.9370
Jump up ^ McCarty, G.W. Modes of action of nitrification inhibitors. Biology and Fertility of Soils, 1998, 29(1), p. 1-9 doi:10.1007/s003740050518
Jump up ^ Topp, E; Knowles, R. Effects of Nitrapyrin [2-Chloro-6-(trichloromethyl) Pyridine] on the Obligate Methanotroph Methylosinus trichosporium OB3b. Appl. Environ. Microbiol. 1984, 47(2), p. 258-262.doi:10.1007/BF01576048
Jump up ^ McCarty, G.W. Modes of action of nitrification inhibitors. Biology and Fertility of Soils, 1998, 29(1), p. 1-9. doi:10.1007/s003740050518
Jump up ^ Knowles, B. Physiology, biochemistry and specific inhibitors of CH4, NH4+, and CO oxidation by methanotrophs and nitrifiers. Microbiol. Rev. 1989, 53, p.68-84.
Jump up ^ Singh, S; Verma, A. The Potential of Nitrification Inhibitors to Manage the Pollution Effect of Nitrogen Fertilizers in Agricultural and Other Soils: A Review. Environmental Practice, 2007, p.266-279. doi:10.1017/S1466046607070482
Jump up ^ Rouse, J; Bishop, C; Struger, J. Nitrogen pollution: an assessment of its threat to amphibian survival. Environ. Health Perspect. 1999, 107(10), p.799-803. doi:10.2307/3454576
External links[edit]
Nitrification at the heart of filtration at fishdoc.co.uk
Nitrification at University of Aberdeen · King's College
Nitrification Basics for Aerated Lagoon Operators at lagoonsonline.com
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