NO_''x'' is a generic term for the mono-nitrogen oxides NO and NO₂ (nitric oxide and nitrogen dioxide). They are produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures. In areas of high motor vehicle traffic, such as in large cities, the amount of nitrogen oxides emitted into the atmosphere as air pollution can be quite significant. NOx gasses are formed everywhere where there is combustion - like in an engine. In atmospheric chemistry, the term means the total concentration of NO and NO₂. NO_''x'' react to form smog and acid rain. NO_''x'' are also central to the formation of tropospheric ozone.

NO_''x'' should not be confused with nitrous oxide (N₂O), which is a greenhouse gas and has many uses as an oxidizer, an anesthetic, and a food additive.

NO_''y'' (reactive odd nitrogen) is defined as the sum of NO_''x'' plus the compounds produced from the oxidation of NO_''x'' which include nitric acid.

Formation and reactions

The oxygen and nitrogen do not react at ambient temperatures. But at high temperatures, they have an endothermic reaction producing various oxides of nitrogen. Such temperatures arise inside an internal combustion engine, combustion of a mixture of air and fuel.

In atmospheric chemistry, the term NO_''x'' means the total concentration of NO and NO₂. During daylight, these concentrations are in equilibrium; the ratio NO/NO₂ is determined by the intensity of sunshine (which converts NO₂ to NO) and the concentration of ozone (which reacts with NO to again form NO₂).

In the presence of excess oxygen (O₂), nitric oxide (NO) reacts with the oxygen to form nitrogen dioxide (NO₂). The time required depends on the concentration in air as shown below:

{|- ! NO concentration in air (ppm) ! Time required for half NO to be oxidized to NO₂ (min) |- |20,000 |0.175 |- |10,000 |0.35 |- | 1,000 | 3.5 |- |100 |35 |- |10 |350 |- |1 |3500 |}

When NO_''x'' and volatile organic compounds (VOCs) react in the presence of sunlight, they form photochemical smog, a significant form of air pollution, especially in the summer. Children, people with lung diseases such as asthma, and people who work or exercise outside are particularly susceptible to adverse effects of smog such as damage to lung tissue and reduction in lung function.

Formation of nitric acid and acid rain

Mono-nitrogen oxides eventually form nitric acid when dissolved in atmospheric moisture, forming a component of acid rain. The following chemical reaction occurs when nitrogen dioxide reacts with water:

:2 NO₂ + H₂O → HNO₂ + HNO₃

Nitrous acid then decomposes as follows:

:3 HNO₂ → HNO₃ + 2 NO + H₂O

where nitric oxide will oxidize to form nitrogen dioxide that again reacts with water, ultimately forming nitric acid:

:4 NO + 3 O₂ + 2 H₂O → 4 HNO₃

Mono-nitrogen oxides are also involved in tropospheric production of ozone.

This nitric acid may end up in the soil, where it makes nitrate, where it is of use to growing plants.

Sources

Natural sources

Nitric oxide is produced during thunderstorms due to the extreme heat of lightning, and is caused by the splitting of nitrogen molecules. This can result in the production of acid rain, if nitrous oxide forms compounds with the water molecules in precipitation, thus creating acid rain.

Biogenic sources

Agricultural fertilization and the use of nitrogen fixing plants also contribute to atmospheric NO_''x'', by promoting nitrogen fixation by microorganisms.

Industrial sources

The three primary sources of NO_''x'' in combustion processes:

thermal NO_''x''

fuel NO_''x''

prompt NO_''x''

Thermal NO_''x'' formation, which is highly temperature dependent, is recognized as the most relevant source when combusting natural gas. Fuel NO_''x'' tends to dominate during the combustion of fuels, such as coal, which have a significant nitrogen content, particularly when burned in combustors designed to minimise thermal NO_''x''. The contribution of prompt NO_''x'' is normally considered negligible. A fourth source, called ''feed NO_''x'''' is associated with the combustion of nitrogen present in the feed material of cement rotary kilns, at between 300° and 800°C, where it is also a minor contributor.

Thermal

Thermal NO_''x'' refers to NO_''x'' formed through high temperature oxidation of the diatomic nitrogen found in combustion air. The formation rate is primarily a function of temperature and the residence time of nitrogen at that temperature. At high temperatures, usually above 1600°C (2900°F), molecular nitrogen (N₂) and oxygen (O₂) in the combustion air disassociate into their atomic states and participate in a series of reactions.

The three principal reactions (the extended Zeldovich mechanism) producing thermal NO_''x'' are:

:N₂ + O → NO + N :N + O₂ → NO + O :N + OH → NO + H

All 3 reactions are reversible. Zeldovich was the first to suggest the importance of the first two reactions. The last reaction of atomic nitrogen with the hydroxyl radical, OH, was added by Lavoie, Heywood and Keck to the mechanism and makes a significant contribution to the formation of thermal NO_''x''.

Fuel

The major source of NO_''x'' production from nitrogen-bearing fuels such as certain coals and oil, is the conversion of fuel bound nitrogen to NO_''x'' during combustion. During combustion, the nitrogen bound in the fuel is released as a free radical and ultimately forms free N₂, or NO. Fuel NO_''x'' can contribute as much as 50% of total emissions when combusting oil and as much as 80% when combusting coal.

Although the complete mechanism is not fully understood, there are two primary paths of formation. The first involves the oxidation of volatile nitrogen species during the initial stages of combustion. During the release and prior to the oxidation of the volatiles, nitrogen reacts to form several intermediaries which are then oxidized into NO. If the volatiles evolve into a reducing atmosphere, the nitrogen evolved can readily be made to form nitrogen gas, rather than NO_''x''. The second path involves the combustion of nitrogen contained in the char matrix during the combustion of the char portion of the fuels. This reaction occurs much more slowly than the volatile phase. Only around 20% of the char nitrogen is ultimately emitted as NO_''x'', since much of the NO_''x'' that forms during this process is reduced to nitrogen by the char, which is nearly pure carbon.

Prompt

This third source is attributed to the reaction of atmospheric nitrogen, N₂, with radicals such as C, CH, and CH₂ fragments derived from fuel, where this cannot be explained by either the aforementioned thermal or fuel processes. Occurring in the earliest stage of combustion, this results in the formation of fixed species of nitrogen such as NH (nitrogen monohydride), HCN (hydrogen cyanide), H₂CN (dihydrogen cyanide) and CN- (cyano radical) which can oxidize to NO. In fuels that contain nitrogen, the incidence of prompt NO_''x'' is especially minimal and it is generally only of interest for the most exacting emission targets.

NO from N₂O

At high pressures NO formation via N₂O becomes important:

:N₂ + O + M → N₂O + M :N₂O + O → 2NO + Activation Energy = 97kJ/mol :N₂O + O → N₂ + O₂

Competing Reactions :

:N₂O + O → NO + N Thermal NO :N₂O + O + M → N₂O + M

:d[N₂]/dt = k[O][N_2] α pressure² :d[N₂]/dt = k[O][N₂][M] α pressure³

Health effects

NO_''x'' reacts with ammonia, moisture, and other compounds to form nitric acid vapor and related particles. Small particles can penetrate deeply into sensitive lung tissue and damage it, causing premature death in extreme cases. Inhalation of such particles may cause or worsen respiratory diseases such as emphysema, bronchitis it may also aggravate existing heart disease.

NO_''x'' reacts with volatile organic compounds in the presence sunlight to form Ozone. Ozone can cause adverse effects such as damage to lung tissue and reduction in lung function mostly in susceptible populations (children, elderly, asthmatics). Ozone can be transported by wind currents and cause health impacts far from the original sources. The American Lung Association estimates that nearly 50 percent of United States inhabitants live in counties that are not in ozone compliance.

NO_''x'' destroys ozone in the stratosphere. Ozone in the stratosphere absorbs ultraviolet light, which is potentially damaging to life on earth. NO_''x'' from combustion sources does not reach the stratosphere; instead, NO_''x'' is formed in the stratosphere from photolysis of nitrous oxide.

NO_''x'' also readily reacts with common organic chemicals, and even ozone, to form a wide variety of toxic products: nitroarenes, nitrosamines and also the nitrate radical some of which may cause biological mutations. Recently another pathway, via NOx, to ozone has been found that predominantly occurs in coastal areas via formation of nitryl chloride when NOx comes into contact with salt mist.

Regulation and emission control technologies

As discussed above, atmospheric NO_''x'' eventually forms nitric acid, which contributes to acid rain. NO_''x'' emissions are regulated in the United States by the Environmental Protection Agency, and in the UK by the Department for Environment, Food and Rural Affairs.

Technologies such as flameless oxidation (FLOX) and staged combustion significantly reduce thermal NO_''x'' in industrial processes. Bowin low NO_''x'' technology is a hybrid of staged-premixed-radiant combustion technology with a major surface combustion preceded by a minor radiant combustion. In the Bowin burner, air and fuel gas are premixed at a ratio greater than or equal to the stoichiometric combustion requirement. Water Injection technology, whereby water is introduced into the combustion chamber, is also becoming an important means of NO_''x'' reduction through increased efficiency in the overall combustion process. Alternatively, the water (e.g. 10 to 50%) is emulsified into the fuel oil prior to the injection and combustion. This emulsification can either be made in-line (unstabilized) just before the injection or as a drop-in fuel with chemical additives for long term emulsion stability (stabilized). Inline emulsified fuel/water mixtures show NO_''x'' reductions between 4 and 83%. Other technologies, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) reduce post combustion NO_''x''.

The use of exhaust gas recirculation and catalytic converters in motor vehicle engines have significantly reduced emissions.

References

C.I. Analytics Category:Oxides Category:Pollutants Category:Smog

ro:NOx de:Stickoxide

Coordinates	6°7′55″N1°13′22″N
name	Eric Whitacre
background	non_performing_personnel
born	January 02, 1970
occupation	Composer Conductor Lecturer
website	ericwhitacre.com
notable instruments	}}

Eric Whitacre (born January 2, 1970 in Reno, Nevada) is an American composer, conductor and lecturer. He is one of the most popular and performed composers of his generation. In 2008, the all-Whitacre choral CD ''Cloudburst'' (released by the British ensemble Polyphony on Hyperion Records) became an international best-seller, topping the classical charts and earning a Grammy nomination. Robert Hollingworth commented: "what hits you straight between the eyes is the honesty, optimism and sheer belief that passes any pretension. This is music that can actually make you smile." Whitacre's Virtual Choir projects on YouTube exposed his music to a new audience. Whitacre signed a long-term recording deal with Decca in 2010 and continues to develop his award winning musical ''Paradise Lost''. A condensed concert version was given at Carnegie Hall in 2010. Plans for the stage show and soundtrack extend into 2011.

Biography

Whitacre began his musical training while an undergraduate at the University of Nevada, Las Vegas, where he studied composition with avant garde Ukrainian composer Virko Baley and choral conducting with David Weiller. He wrote his setting of ''Go, Lovely Rose'' for his college choir and presented the composition as a gift to David Weiller. Eric went on to earn his Master's degree in composition at the Juilliard School, where he studied with John Corigliano. His works ''Water Night'', ''Cloudburst'', ''Sleep'', ''Lux Aurumque'', ''A Boy and a Girl'' and "The Seal Lullaby" are amongst the most popular choral works in the standard repertory; his ''Ghost Train'', ''Godzilla Eats Las Vegas'' and ''October'' and "Equus" have achieved similar success in the symphonic wind community. His cutting edge musical ''Paradise Lost: Shadows and Wings'', which combines influences including trance, electronica, and anime with choral, cinematic, and operatic traditions, won the ASCAP Harold Arlen Award, the Richard Rogers award, and 10 Ovation Award nominations. He has received composition awards from the Barlow International Composition Competition, the American Choral Directors Association and the American Composers Forum. In 2001, Whitacre became the youngest recipient ever awarded the Raymond C. Brock commission by the American Choral Directors Association.

Since 2000, he has conducted concerts of his choral and symphonic music in Japan, Australia, China, Singapore, South America and much of Europe, as well as in American Universities and colleges where he regularly conducts seminars and lectures with young musicians. 2010-11 commissions include works for Chanticleer, The King's Singers, Julian Lloyd Webber, and The London Symphony Orchestra and Chorus.

Whitacre's first recording, ''The Music of Eric Whitacre'', was named by the American Record Guide as one of the top ten classical albums of 1997. In 2006, a full collection of his a cappella music, ''Cloudburst and Other Choral Works'', was released on the British label Hyperion Records. The album became an international best seller, appearing in the top ten of both Billboard's and iTunes Top Classical Albums charts. Two years after its release, it continues to be a top-seller and won a 2007 Grammy nomination for Best Choral Performance. In 2010, Whitacre signed a long-term contract with Decca as a performer. "Light & Gold," Whitacre's first album with the label, was released in October 2010, and features Whitacre himself as conductor and musical director.

In October 2010 Whitacre was named Composer-in-Residence and Visiting Fellow at Sidney Sussex College, Cambridge University. He lived on campus for the duration of the 2010 Michaelmas term. In March 2011 it was announced that he had joined the fashion models agency, Storm.

Whitacre is married to Grammy-award winning soprano Hila Plitmann.

Style

Whitacre writes music that incorporates contemporary sounds and influences while demanding precision, intonation and ensemble. He is probably best known for his choral works; however, both his choral and instrumental styles use his signature "Whitacre chords," or pan-diatonic clusters usually arranged in successive increasing or decreasing density. Whitacre achieves this growth and decay by splitting voices ''divisi''—in one case up to 18 parts. These sonorities can often be read as seventh or ninth chords, with or without suspended seconds and fourths. Perhaps his most famous chord is a root-position major triad with an added major second and/or perfect fourth. Whitacre makes frequent use of quartal, quintal and secundal harmonies, and is also known for his use of unconventional chord progressions. His use of rhythm often involves mixed, complex, and/or compound meters. His pieces sometimes include frequent meter changes and unusual rhythmic patterns. Another trademark of Whitacre's pieces is the use of aleatoric and indeterminate sections, as well as unusual score instructions involving, in some cases, hand actions and/or props.

Projects

Virtual Choir

Whitacre's Virtual Choir projects were inspired by a video sent to him of a young girl singing one of his choral pieces he then began with a test run of ''Sleep'', then ''Lux Aurumque'' in 2009 and was followed again by ''Sleep'' in 2010. The video for ''Lux Aurumque'', featuring a virtual choir of 185 voices from 12 countries, was described as a "musical experience that works better than anyone might have expected", their video receiving over 1,000,000 hits in the first two months of its release.

The 2010 version of the Virtual Choir 2.0 "Sleep" began in October 2010 and the video submission process was completed on 10 January 2011. Whitacre spoke at TED.com and this video was released on April 1, 2011, accompanied with a short 2 minute example of the "Sleep" project. The YouTube release was on April 7, 2011.

Recording projects

Whitacre's first album with Decca, Light & Gold was released in October 2010. From October to December 2010, Whitacre was a visiting Fellow at Sidney Sussex College, Cambridge during Michaelmas (Autumn) Term. He composed a piece for the college choir, and worked with students in masterclasses and workshops. The concert version of his musical ''Paradise Lost: Shadows and Wings'' was performed to a sold out audience at Carnegie Hall in June 2010.

Performance projects

Whitacre has worked collaboratively with Distinguished Concerts International New York (DCINY) and is due to collaborate with them again in 2011 in New York, Vancouver and Los Angeles. With regard to his musical "Paradise Lost: Shadows and Wings", he was described by the New York Times as a "younger, hipper Andrew Lloyd Webber, with fleeting hints of Bernstein and Sondheim".

On 24 October 2010, he conducted an all-American programme with the London Symphony Orchestra and Chorus at the Barbican London, in a performance that featured his commission for the London Symphony Chorus entitled ''Songs of Immortality''. On 28 November 2010, he sat on the panel of judges for the final episode of Choir of the Year, broadcast on BBC Four and BBC Radio 3. In December 2010, Whitacre conducted the I Vocalisti choir in Hamburg, and was a guest conductor of the Christmas performance of the Berlin Rundfunkchor.

On 6 November 2010, Whitacre conducted Côrdydd, a Cardiff-based mixed choir, and friends in a concert of his work at the BBC Hoddinott Hall in the Wales Millennium Centre.

Whitacre is a founding member of BCM International, a quartet of composers consisting of himself, Steven Bryant, Jonathan Newman and James Bonney, which aspires to "enrich the wind ensemble repertoire with music unbound by traditional thought or idiomatic cliché."

Awards and honors

Whitacre has won awards from the Barlow international composition competition, American Choral Directors Association, American Composers' Forum and in 2001 became the youngest recipient ever of The Raymond C Brock Commission given by the American Choral Directors Association. His musical ''Paradise Lost: Shadows and Wings'' earned him a ASCAP Richard Rodgers Award|Richard Rodgers Award and received 10 nominations at the 2007 Los Angeles Stage Alliance Ovation Awards. The album ''Cloudburst and Other Choral Works'' received a Grammy nomination in 2007 for Best Choral Performance.

Works

Wind symphony

Equus

Ghost Train Triptych

* Ghost Train

* At the Station

* Motive Revolution

Godzilla Eats Las Vegas!

Noisy Wheels of Joy

October

Sleep (choral transcription)

The Seal Lullaby (choral transcription for wind symphony and piano)

Lux Aurumque (choral transcription, transposed a semitone lower from C-Sharp Minor to C Minor)

Cloudburst (choral transcription)

Libertas Imperio (From Paradise Lost: Shadows and Wings)

SATB choral

Animal Crackers, Volume 1 (Poems by Ogden Nash)

* The Panther

* The Cow

* The Firefly

Animal Crackers, Volume 2 (Poems by Ogden Nash)

* The Canary

* The Eel

* The Kangaroo

A Boy and A Girl (poem by Octavio Paz)

Cloudburst (poem by Octavio Paz)

Five Hebrew Love Songs (poem by Hila Plitmann)

* Temuna

* Kala Kalla (Light Bride)

* Larov (Mostly)

* Eyze Sheleg! (What snow!)

* Rakut (Tenderness)

Her Sacred Spirit Soars (poem by Charles Anthony Silvestri)

Leonardo Dreams of His Flying Machine (libretto by Charles Anthony Silvestri)

Little Birds (poem by Octavio Paz)

little tree (poem by E. E. Cummings)

Lux Aurumque (poem by Edward Esch; translated into Latin by Charles Anthony Silvestri) (also set for male chorus)

Nox Aurumque (poem by Charles Anthony Silvestri)

The Seal Lullaby (poem by Rudyard Kipling)

She Weeps Over Rahoon (poem by James Joyce)

Sleep (originally a setting of Robert Frost's poem, "Stopping by Woods on a Snowy Evening"; for copyright reasons the published version uses a specially-written text by Charles Anthony Silvestri)

Sleep, My Child (Choral transcription from Paradise Lost: Shadows and Wings)

The Stolen Child (setting of a poem by William Butler Yeats, commissioned in 2008 by the National Youth Choir of Great Britain and The King's Singers for their respective 25th and 40th anniversaries)

This Marriage (poem by Jalal al-Din Rumi)

Three Flower Songs

* I Hide Myself (poem by Emily Dickinson)

* With a Lily in Your Hand (poem by Federico García Lorca)

* Go, Lovely Rose (poem by Edmund Waller)

Three Songs of Faith (poems by E. E. Cummings))

** i will wade out

* hope, faith, life, love

i thank You God for most this amazing day

Water Night (poem by Octavio Paz; translated by Muriel Rukeyser)

When David Heard (from II Samuel 18:33)

Winter (poem by Edward Esch)

What If (lyrics by David Norona and Eric Whitacre)

SSA choral

She Weeps Over Rahoon (text by James Joyce)

Five Hebrew Love Songs (poem by Hila Plitmann)

The Seal Lullaby (text by Rudyard Kipling)

TTBB choral

Lux Aurumque (poem by Edward Esch, translated into Latin by Charles Anthony Silvestri)

The Seal Lullaby (text by Rudyard Kipling)

Choral works not yet published

The City and the Sea (poems by e. e. Cummings)

* i walked the boulevard

* the moon is hiding in her hair

* maggie and millie and molly and may

* as is the sea marvelous (commissioned by the Greater Washington Independent Schools Choral Festival)

* little man in a hurry (Written for Mahtomedi High School, among others.)

Songs of Immortality

* Lie still, sleep becalmed (poem by Dylan Thomas)

After Great Pain (poem by Emily Dickenson)

Orchestral

October

Winter

A Boy and a Girl

Lux Aurumque

Water Night

The River Cam

Solo voice

The City and the Sea (poems by e. e. Cummings)

Five Hebrew Love Songs (poem by Hila Plitmann)

Orchestra

Winter (for strings, choir and sitar)

Music theatre

Paradise Lost: Shadows and Wings, a musical featuring electronic, world, and orchestral instruments; classical singers; and many different styles of music.

Other arrangements

Rak HaHatchala (Only the Beginning) [aka Five Hebrew Love Songs]; for soprano voice, solo violin, piano

Publishers

Whitacre is published by Chester Music; G. Schirmer; Walton Music; Santa Barbara Music; Shadow Water Music; and Carpe Ranam Music.

References

External links

Eric_Whitacre on WikiMusicGuide

Biography on Hyperion Records

NPR Review of ''Cloudburst'' and choral audio. September 28, 2006

Music Productions Ltd (Management company of Eric Whitacre)

Eric Whitacre write-up on ChesterNovello web site

TED about the virtual choir">Eric talking at TED about the virtual choir

Eric Whitacre's Virtual Choir 2.0, 'Sleep'

Classical Archives Interview

Category:1970 births Category:Living people Category:20th-century classical composers Category:21st-century classical composers Category:American composers Category:Concert Band composers Category:University of Nevada, Las Vegas alumni Category:Juilliard School alumni

af:Eric Whitacre de:Eric Whitacre fr:Eric Whitacre it:Eric Whitacre he:אריק וייטאקר nl:Eric Whitacre ja:エリック・ウィテカー no:Eric Whitacre sv:Eric Whitacre