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{{Image|CarbonMonoxideProps.png|right|264px}} '''Carbon monoxide''' (CO), also referred to as '''carbonous oxide''', is a colorless, odorless, and tasteless [[gas]] that is slightly lighter than air. Exposure to high levels of carbon monoxide is extremely toxic to humans and animals. Conversely, small amounts of carbon monoxide are produced in normal animal metabolism and it is thought to have some normal biological functions.
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[[File:Crude oil-fired power plant.jpg|thumb|right|225px|Industrial air pollution source]]
Atmospheric dispersion modeling is the mathematical simulation of how air pollutants disperse in the ambient atmosphere. It is performed with computer programs that solve the mathematical equations and algorithms which simulate the pollutant dispersion. The dispersion models are used to estimate or to predict the downwind concentration of air pollutants emitted from sources such as industrial plants, vehicular traffic or accidental chemical releases.  


Carbon monoxide consists of one [[carbon]] [[atom]] and one [[oxygen]] atom. It is the simplest member of the class of inorganic compounds known as [[oxocarbons]] which includes [[carbon dioxide]] (CO<sub>2</sub>), [[carbon suboxide]] (C<sub>3</sub>O<sub>2</sub>), [[mellitic anhydride]] (C<sub>12</sub>O<sub>9</sub>) and many others. When combined with a metal (i.e., an [[organometallic]] complex), the carbon monoxide is a [[ligand]] called ''carbonyl''&thinsp;: for example, in nickel carbonyl with the formula Ni(CO)<sub>4</sub>.
Such models are important to governmental agencies tasked with protecting and managing the ambient air quality. The models are typically employed to determine whether existing or proposed new industrial facilities are or will be in compliance with the National Ambient Air Quality Standards (NAAQS) in the United States or similar regulations in other nations. The models also serve to assist in the design of effective control strategies to reduce emissions of harmful air pollutants. During the late 1960's, the Air Pollution Control Office of the U.S. Environmental Protection Agency (U.S. EPA) initiated research projects to develop models for use by urban and transportation planners.<ref>J.C. Fensterstock et al, "Reduction of air pollution potential through environmental planning", ''JAPCA'', Vol. 21, No. 7, 1971.</ref>


Carbon monoxide is produced by the partial [[combustion]] of carbon-containing substances. It is produced when there is not enough [[oxygen]] to form carbon dioxide, such as when operating a stove or an [[Gasoline/Draft#Octane_rating|internal combustion engine]] in an enclosed space.
Air dispersion models are also used by emergency management personnel to develop emergency plans for accidental chemical releases. The results of dispersion modeling, using worst case accidental releases and meteorological conditions, can provide estimated locations of impacted areas and be used to determine appropriate protective actions. At industrial facilities in the United States, this type of consequence assessment or emergency planning is required under the Clean Air Act (CAA) codified in Part 68 of Title 40 of the Code of Federal Regulations.


In the presence of oxygen, carbon monoxide burns with a blue flame, producing carbon dioxide.<ref name=Thompson/> Coal gas, which was widely used before the 1960s for domestic lighting, cooking, and heating, had carbon monoxide as a significant constituent. Iron smelting and other current technological processes still produce byproduct carbon monoxide.<ref name=Ayres/>
The dispersion models vary depending on the mathematics used to develop the model, but all require the input of data that may include:


Worldwide, the largest source of carbon monoxide is from the photochemical reactions in the [[Earth's_atmosphere#Structure_of_the_atmosphere|troposphere]] that generate about 5 x 10<sup>12</sup> kilograms per year.<ref name=Weinstock/> Other natural sources of CO include [[volcano|volcanoes]], forest fires, and other forms of combustion.
* Meteorological conditions such as wind speed and direction, the amount of atmospheric turbulence (as characterized by what is called the "stability class"), the ambient air temperature, the height to the bottom of any inversion aloft that may be present, cloud cover and solar radiation.
* The emission parameters such the type of source (i.e., point, line or area), the mass flow rate, the source location and height, the source exit velocity, and the source exit temperature.
* Terrain elevations at the source location and at receptor locations, such as nearby homes, schools, businesses and hospitals.
* The location, height and width of any obstructions (such as buildings or other structures) in the path of the emitted gaseous plume as well as the terrain surface roughness (which may be characterized by the more generic parameters "rural" or "city" terrain).


==Toxicity==
Many of the modern, advanced dispersion modeling programs include a pre-processor module for the input of meteorological and other data, and many also include a post-processor module for graphing the output data and/or plotting the area impacted by the air pollutants on maps. The plots of areas impacted usually include isopleths showing areas of pollutant concentrations that define areas of the highest health risk. The isopleths plots are useful in determining protective actions for the public and first responders.
{{Image|ToxicEffects.png|right|315px}}Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. It combines with hemoglobin in the red blood cells of humans and animals to produce carboxy hemoglobin, which is ineffective for delivering oxygen to bodily tissues. Exposure to carbon monoxide levels as low as 667 parts per million by volume (ppmv) may cause up to 50 % of the body's hemoglobin to convert to carboxyhemoglobin<ref name=Tikuisis/> which may result in seizure, coma, and fatality.


The adjacent table lists the typical symptoms caused by exposure to various concentrations of carbon monoxide, expressed in [[Parts per notation|parts per million by volume]] (ppmv).
The atmospheric dispersion models are also known as atmospheric diffusion models, air dispersion models, air quality models, and air pollution dispersion models.


On average, exposures to levels of 100 ppm or greater is dangerous to human health. In the [[United States]], the long-term workplace exposure levels are limited by the [[Occupational Safety and Health Administration]] (OSHA) to less than 50 ppmv averaged over an 8-hour period;<ref name=OSHAguideline/> in addition, employees are to be removed from any confined space if an upper limit (ceiling) of 100 ppmv is reached.
==Atmospheric layers==


The most common symptoms of carbon monoxide poisoning may resemble other types of poisonings and infections, including symptoms such as headache, nausea, vomiting, dizziness, fatigue, and a feeling of weakness. Infants may be irritable and feed poorly.<ref name=Blumenthal/> Neurological signs include confusion, disorientation, visual disturbance, fainting and seizures.  
Discussion of the layers in the Earth's atmosphere is needed to understand where airborne pollutants disperse in the atmosphere. The layer closest to the Earth's surface is known as the ''troposphere''. It extends from sea-level up to a height of about 18 km and contains about 80 percent of the mass of the overall atmosphere. The ''stratosphere'' is the next layer and extends from 18 km up to about 50 km. The third layer is the ''mesosphere'' which extends from 50 km up to about 80 km. There are other layers above 80 km, but they are insignificant with respect to atmospheric dispersion modeling.


Exposures to carbon monoxide may cause significant damage to the heart and central nervous system, especially to a sub-cortical component of the brain, often with long-term effects.  
The lowest part of the troposphere is called the ''atmospheric boundary layer (ABL)'' or the ''planetary boundary layer (PBL)'' and extends from the Earth's surface up to about 1.5 to 2.0 km in height. The air temperature of the atmospheric boundary layer decreases with increasing altitude until it reaches what is called the ''inversion layer'' (where the temperature increases with increasing altitude) that caps the atmospheric boundary layer. The upper part of the troposphere (i.e., above the inversion layer) is called the ''free troposphere'' and it extends up to the 18 km height of the troposphere.


Carbon monoxide may have severe adverse effects on the fetus of a pregnant woman.
The ABL is the most important layer with respect to the emission, transport and dispersion of airborne pollutants. The part of the ABL between the Earth's surface and the bottom of the inversion layer is known as the ''mixing layer''. Almost all of the airborne pollutants emitted into the ambient atmosphere are transported and dispersed within the mixing layer. Some of the emissions penetrate the inversion layer and enter the free troposphere above the ABL.


==Occurrence==
In summary, the layers of the Earth's atmosphere from the surface of the ground upwards are: the ABL made up of the mixing layer capped by the inversion layer; the free troposphere; the stratosphere; the mesosphere and others. Many atmospheric dispersion models are referred to as ''boundary layer models'' because they mainly model air pollutant dispersion within the ABL. To avoid confusion, models referred to as ''mesoscale models'' have dispersion modeling capabilities that can extend horizontally as much as  a few hundred kilometres. It does not mean that they model dispersion in the mesosphere.


Carbon monoxide occurs in various natural and artificial environments. Typical concentrations in parts per million by volume are as follows:<ref name=NationalAcademy/><ref name=EPAiaq/><ref name=Gosink/><br />
==Gaussian air pollutant dispersion equation==
<br />
<span style="align:left; clear:right; display:image; margin-left:15px; ">[[Image:CarbonMonoxideConcentrations.png]]</span>


===Atmosphere===
The technical literature on air pollution dispersion is quite extensive and dates back to the 1930s and earlier. One of the early air pollutant plume dispersion equations was derived by Bosanquet and Pearson.<ref>C.H. Bosanquet and J.L. Pearson, "The spread of smoke and gases from chimneys", ''Trans. Faraday Soc.'', 32:1249, 1936.</ref> Their equation did not assume Gaussian distribution nor did it include the effect of ground reflection of the pollutant plume.


Carbon monoxide is present in low levels in the [[Earth's atmosphere|atmosphere]], primarily as a product of [[volcano|volcanic activity]] but also from natural and man-made fires such as slash and burn agriculture, burning of crop residues, and sugarcane fire-cleaning. [[Combustion]] of [[fossil fuels]] also results in carbon monoxide [[Air pollution emissions|emissions]] to the atmosphere.
Sir Graham Sutton derived an air pollutant plume dispersion equation in 1947<ref>O.G. Sutton, "The problem of diffusion in the lower atmosphere", ''QJRMS'', 73:257, 1947.</ref><ref>O.G. Sutton, "The theoretical distribution of airborne pollution from factory chimneys", ''QJRMS'', 73:426, 1947.</ref> which did include the assumption of Gaussian distribution for the vertical and crosswind dispersion of the plume and also included the effect of ground reflection of the plume.


Through natural processes in the atmosphere, carbon monoxide is eventually converted to [[carbon dioxide]]. Carbon monoxide concentrations in the atmosphere are short-lived and geographically variable.
Under the stimulus provided by the advent of stringent environmental control regulations, there was an immense growth in the use of air pollutant plume dispersion calculations between the late 1960s and today. A great many computer programs for calculating the dispersion of air pollutant emissions were developed during that period of time and they were commonly called "air dispersion models". The basis for most of those models was the '''Complete Equation For Gaussian Dispersion Modeling Of Continuous, Buoyant Air Pollution Plumes''' shown below:<ref name=Beychok>{{cite book|author=M.R. Beychok|title=Fundamentals Of Stack Gas Dispersion|edition=4th Edition| publisher=author-published|year=2005|isbn=0-9644588-0-2}}.</ref><ref>{{cite book|author=D. B. Turner| title=Workbook of atmospheric dispersion estimates: an introduction to dispersion modeling| edition=2nd Edition |publisher=CRC Press|year=1994|isbn=1-56670-023-X}}.</ref>


===Urban areas===


Carbon monoxide is a major atmospheric pollutant in most urban areas, chiefly from the engine exhausts of vehicles, portable and back-up generators, lawn mowers, leaf blowers, etc. One of the most important cases of carbon monoxide buildup is in the presence of urban street canyons or other semi-enclosed volumes created by man-made structures. The incomplete combustion of various other fuels such as [[natural gas]], [[fuel oil]]s, [[coal]], [[wood]], [[charcoal]], [[Liquefied natural gas#LPG.2C a somewhat similar substance|LPG]], and trash also contribute to the emissions of carbon monoxide in urban areas.
<math>C = \frac{\;Q}{u}\cdot\frac{\;f}{\sigma_y\sqrt{2\pi}}\;\cdot\frac{\;g_1 + g_2 + g_3}{\sigma_z\sqrt{2\pi}}</math>


===Indoors===
{| border="0" cellpadding="2"
|-
|align=right|where:
|&nbsp;
|-
!align=right|<math>f</math> 
|align=left|= crosswind dispersion parameter
|-
!align=right|&nbsp;
|align=left|= <math>\exp\;[-\,y^2/\,(2\;\sigma_y^2\;)\;]</math>
|-
!align=right|<math>g</math>
|align=left|= vertical dispersion parameter = <math>\,g_1 + g_2 + g_3</math>
|-
!align=right|<math>g_1</math>
|align=left|= vertical dispersion with no reflections
|-
!align=right|&nbsp;
|align=left|= <math>\; \exp\;[-\,(z - H)^2/\,(2\;\sigma_z^2\;)\;]</math>
|-
!align=right|<math>g_2</math>
|align=left|= vertical dispersion for reflection from the ground
|-
!align=right|&nbsp;
|align=left|= <math>\;\exp\;[-\,(z + H)^2/\,(2\;\sigma_z^2\;)\;]</math>
|-
!align=right|<math>g_3</math>
|align=left|= vertical dispersion for reflection from an inversion aloft
|-
!align=right|&nbsp;
|align=left|= <math>\sum_{m=1}^\infty\;\big\{\exp\;[-\,(z - H - 2mL)^2/\,(2\;\sigma_z^2\;)\;]</math>
|-
!align=right|&nbsp;
|align=left|&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <math>+\, \exp\;[-\,(z + H + 2mL)^2/\,(2\;\sigma_z^2\;)\;]</math>
|-
!align=right|&nbsp;
|align=left|&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <math>+\, \exp\;[-\,(z + H - 2mL)^2/\,(2\;\sigma_z^2\;)\;]</math>
|-
!align=right|&nbsp;
|align=left|&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <math>+\, \exp\;[-\,(z - H + 2mL)^2/\,(2\;\sigma_z^2\;)\;]\big\}</math>
|-
!align=right|<math>C</math>
|align=left|= concentration of emissions, in g/m³, at any receptor located:
|-
!align=right|&nbsp;
|align=left|&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; x meters downwind from the emission source point
|-
!align=right|&nbsp;
|align=left|&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; y meters crosswind from the emission plume centerline
|-
!align=right|&nbsp;
|align=left|&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; z meters above ground level
|-
!align=right|<math>Q</math>
|align=left|= source pollutant emission rate, in g/s
|-
!align=right|<math>u</math>
|align=left|= horizontal wind velocity along the plume centerline, m/s
|-
!align=right|<math>H</math>
|align=left|= height of emission plume centerline above ground level, in m
|-
!align=right|<math>\sigma_z</math>
|align=left|= vertical standard deviation of the emission distribution, in m
|-
!align=right|<math>\sigma_y</math>
|align=left|= horizontal standard deviation of the emission distribution, in m
|-
!align=right|<math>L</math>
|align=left|= height from ground level to bottom of the inversion aloft, in m
|-
!align=right|<math>\exp</math>
|align=left|= the exponential function
|}


Indoors and in other closed environments, the concentration of carbon monoxide can quickly and unnoticeably rise to dangerous and fatal levels. The true number of incidents of carbon monoxide poisoning is unknown, since many non-fatal exposures go undetected and unreported. Carbon monoxide poisoning is the most common cause of injury and death due to poisoning worldwide. Poisoning is typically more common during the winter months, probably because of the increased domestic use of gas furnaces, gas or kerosene space heaters, and kitchen stoves during the winter months, which if faulty and/or used without enough ventilation, may produce excessive carbon monoxide.<ref name=Thom/><ref name=Ernst/><ref name=Heckerling/>
The above equation not only includes upward reflection from the ground, it also includes downward reflection from the bottom of any inversion lid present in the atmosphere.


In many industrialized countries carbon monoxide is the cause of more than 50 % of fatal poisonings.<ref name=Omaye/> It has been estimated that more than 40,000 people per year seek medical attention for carbon monoxide poisoning in the United States.<ref name=Hampson/> Approximately 200 people die each year in the USA from carbon monoxide poisoning caused by home fuel-burning heating equipment.<ref name=CPSC/> Carbon monoxide poisoning contributes to the approximately 5613 smoke inhalation deaths each year in the United States.<ref name=Cobb/> The [[Centers for Disease Control and Prevention]] (CDC) reports, "Each year, more than 500 Americans die from unintentional carbon monoxide poisoning, and more than 2000 commit suicide by intentionally poisoning themselves."<ref name=CDC/>
The sum of the four exponential terms in <math>g_3</math> converges to a final value quite rapidly. For most cases, the summation of the series with '''''m''''' = 1, '''''m''''' = 2 and '''''m''''' = 3 will provide an adequate solution.


==Uses==
<math>\sigma_z</math> and <math>\sigma_y</math> are functions of the atmospheric stability class (i.e., a measure of the turbulence in the ambient atmosphere) and of the downwind distance to the receptor. The two most important variables affecting the degree of pollutant emission dispersion obtained are the height of the emission source point and the degree of atmospheric turbulence. The more turbulence, the better the degree of dispersion.
===Chemical industry===


Carbon monoxide gas has many applications in large-scale [[Chemical plant|chemicals manufacturing]]. Large quantities of [[aldehydes]] are produced by the hydroformylation reaction of [[alkene]]s, carbon monoxide, and [[hydrogen]]. Hydroformylation is coupled to Shell Chemical's Higher Olefin Process (SHOP) to produced detergent precursors.
Whereas older models rely on stability classes for the determination of <math>\sigma_y</math> and <math>\sigma_z</math>, more recent models increasingly rely on Monin-Obukhov similarity theory to derive these parameters.


[[Methanol]] is produced by the hydrogenation of carbon monoxide. In a related reaction, the hydrogenation of carbon monoxide is coupled to C-C bond formation, as in the [[Fischer-Tropsch]] process which can be used to convert carbon monoxide into liquid [[hydrocarbon]] fuels.
==Briggs plume rise equations==


In the Monsanto process, carbon monoxide and methanol react in the presence of a [[rhodium]] [[Catalysis|catalyst]] and [[hydroiodic]] acid to produce [[acetic acid]].
The Gaussian air pollutant dispersion equation (discussed above) requires the input of ''H'' which is the pollutant plume's centerline height above ground level. ''H'' is the sum of ''H''<sub>s</sub> (the actual physical height of the pollutant plume's emission source point) plus Δ''H'' (the plume rise due the plume's buoyancy).


Another industrial use for pure carbon monoxide is the Mond process, sometimes called the Carbonyl process, which is utilized to extract and purify of [[nickel]] from the raw nickel ore.
[[File:Gaussian Plume.png|thumb|right|333px|Visualization of a buoyant Gaussian air pollutant dispersion plume]]


===Medicine===
To determine Δ''H'', many if not most of the air dispersion models developed between the late 1960s and the early 2000s used what are known as "the Briggs equations." G.A. Briggs first published his plume rise observations and comparisons in 1965.<ref>G.A. Briggs, "A plume rise model compared with observations", ''JAPCA'', 15:433–438, 1965.</ref> In 1968, at a symposium sponsored by CONCAWE (a Dutch organization), he compared many of the plume rise models then available in the literature.<ref>G.A. Briggs, "CONCAWE meeting: discussion of the comparative consequences of different plume rise formulas", ''Atmos. Envir.'', 2:228–232, 1968.</ref> In that same year, Briggs also wrote the section of the publication edited by Slade<ref>D.H. Slade (editor), "Meteorology and atomic energy 1968", Air Resources Laboratory, U.S. Dept. of Commerce, 1968.</ref> dealing with the comparative analyses of plume rise models.  That was followed in 1969 by his classical critical review of the entire plume rise literature,<ref>G.A. Briggs, "Plume Rise", ''USAEC Critical Review Series'', 1969.</ref> in which he proposed a set of plume rise equations which have become widely known as "the Briggs equations".  Subsequently, Briggs modified his 1969 plume rise equations in 1971 and in 1972.<ref>G.A. Briggs, "Some recent analyses of plume rise observation", ''Proc. Second Internat'l. Clean Air Congress'', Academic Press, New York, 1971.</ref><ref>G.A. Briggs, "Discussion: chimney plumes in neutral and stable surroundings", ''Atmos. Envir.'', 6:507–510, 1972.</ref>


Following the first report that carbon monoxide is a normal neurotransmitter in 1993,<ref name=NYTimes/> as well as one of three gases that naturally modulate inflammatory responses in the body (the other two being [[nitric oxide]] and [[hydrogen sulfide]]), carbon monoxide has received a considerable attention as a biological regulator. All three gases are known to act as vasodilators, and encouragers of neovascular growth.<ref name=LingLi/> However, the issues are complex, as neovascular growth is not always beneficial, since it plays a role in tumor growth, and also the damage from wet macular degeneration, a disease for which smoking (a major source of carbon monoxide in the blood, several times more than natural) increases the risk by a factor of about five.
Briggs divided air pollution plumes into these four general categories:
* Cold jet plumes in calm ambient air conditions
* Cold jet plumes in windy ambient air conditions
* Hot, buoyant plumes in calm ambient air conditions
* Hot, buoyant plumes in windy ambient air conditions


Many laboratory studies worldwide have been made of the anti-inflammatory and cytoprotective properties of carbon monoxide. These properties have the potential to prevent the development of pathological conditions such as ischemia reperfusion injury, transplant rejection, atherosclerosis, severe sepsis, severe malaria, or autoimmunity. Clinical tests involving humans have been performed, however the results have not yet been released.<ref name=BostonGlobe/>
Briggs considered the trajectory of cold jet plumes to be dominated by their initial velocity momentum, and the trajectory of hot, buoyant plumes to be dominated by their buoyant momentum to the extent that their initial velocity momentum was relatively unimportant. Although Briggs proposed plume rise equations for each of the above plume categories, '''''it is important to emphasize that "the Briggs equations" which become widely used are those that he proposed for bent-over, hot buoyant plumes'''''.


===Meat coloring===
In general, Briggs's equations for bent-over, hot buoyant plumes are based on observations and data involving plumes from typical combustion sources such as the flue gas stacks from steam-generating boilers burning fossil fuels in large power plants.  Therefore the stack exit velocities were probably in the range of 20 to 100 ft/s (6 to 30 m/s) with exit temperatures ranging from 250 to 500 °F (120 to 260 °C).


Carbon monoxide is used in modified atmosphere packaging systems in the United States, mainly with fresh meat products to keep them looking fresh. The carbon monoxide combines with myoglobin to form carboxymyoglobin, a bright-cherry-red pigment. This stable red color can persist much longer than in normally packaged meat.<ref name=Oddvin/> Typical levels of carbon monoxide involved in the facilities that use this process are between 0.4 to 0.5 percent by volume.
A logic diagram for using the Briggs equations<ref name=Beychok/> to obtain the plume rise trajectory of bent-over buoyant plumes is presented below:
[[Image:BriggsLogic.png|none]]
:{| border="0" cellpadding="2"
|-
|align=right|where:
|&nbsp;
|-
!align=right| Δh
|align=left|= plume rise, in m
|-
!align=right| F<sup>&nbsp;</sup> <!-- The HTML is needed to line up characters. Do not remove.-->
|align=left|= buoyancy factor, in m<sup>4</sup>s<sup>−3</sup>
|-
!align=right| x
|align=left|= downwind distance from plume source, in m
|-
!align=right| x<sub>f</sub>
|align=left|= downwind distance from plume source to point of maximum plume rise, in m
|-
!align=right| u
|align=left|= windspeed at actual stack height, in m/s
|-
!align=right| s<sup>&nbsp;</sup> <!-- The HTML is needed to line up characters. Do not remove.-->
|align=left|= stability parameter, in s<sup>−2</sup>
|}
The above parameters used in the Briggs' equations are discussed in Beychok's book.<ref name=Beychok/>


The technology was first given "generally recognized as safe" (GRAS) status by the [[U.S. Food and Drug Administration]] (FDA) in 2002 for use as a secondary packaging system, and does not require labeling. In 2004, the FDA approved the use of carbon monoxide in packaging, declaring that it does not mask any spoilage odor.<ref name=Eilert/> Despite this ruling, the process remains controversial for fear that it masks spoilage.<ref name=FoodSafety/> The process is prohibited in many countries, including [[Canada]], [[Japan]], [[Singapore]] and the [[European Union]].
==References==
{{reflist}}
 
== Further reading==
 
*{{cite book | author=M.R. Beychok| title=Fundamentals Of Stack Gas Dispersion | edition=4th Edition | publisher=author-published | year=2005 | isbn=0-9644588-0-2}}
 
*{{cite book | author=K.B. Schnelle and P.R. Dey| title=Atmospheric Dispersion Modeling Compliance Guide  | edition=1st Edition| publisher=McGraw-Hill Professional | year=1999 | isbn=0-07-058059-6}}
 
*{{cite book | author=D.B. Turner| title=Workbook of Atmospheric Dispersion Estimates: An Introduction to Dispersion Modeling | edition=2nd Edition | publisher=CRC Press | year=1994 | isbn=1-56670-023-X}}
 
*{{cite book | author= S.P. Arya| title=Air Pollution Meteorology and Dispersion | edition=1st Edition | publisher=Oxford University Press | year=1998 | isbn=0-19-507398-3}}
 
*{{cite book | author=R. Barrat| title=Atmospheric Dispersion Modelling | edition=1st Edition | publisher=Earthscan Publications | year=2001 | isbn=1-85383-642-7}}


==References==
*{{cite book | author=S.R. Hanna and R.E. Britter| title=Wind Flow and Vapor Cloud Dispersion at Industrial and Urban Sites  | edition=1st Edition | publisher=Wiley-American Institute of Chemical Engineers | year=2002 | isbn=0-8169-0863-X}}
{{reflist|refs=


<ref name=Thompson>[http://www.chm.bris.ac.uk/motm/co/coh.htm Carbon Monoxide - Molecule of the Month], Dr. Mike Thompson, Winchester College, UK.</ref>
*{{cite book | author=P. Zannetti| title=Air pollution modeling : theories, computational methods, and available software | edition= | publisher= Van Nostrand Reinhold | year=1990 | isbn=0-442-30805-1 }}
<ref name=Ayres>Edward H.Ayres (2009), <i>Crossing the Energy Divide: Moving from Fossil Fuel Dependence to a Clean-Energy Future</i>, Wharton School Publishing, ISBN 0137015445.</ref>
<ref name=Weinstock>B. Weinstock and H. Niki (1972), &quot;Carbon Monoxide Balance in Nature&quot;, <i>Science</i>, Vol. 176, Issue 4032, pp. 290-292.</ref>
<ref name=Tikuisis>P. Tikuisis, D.M. Kane, T.M. McLellan, F. Buick and S.M. Fairburn (1992), &quot;Rate of formation of carboxyhemoglobin in exercising humans exposed to carbon monoxide&quot;, <i>Journal of Applied Physiology</i>, Vol. 72, Issue 4, pp. 1311-9.</ref>
<ref name=OSHAguideline>[http://www.osha.gov/SLTC/healthguidelines/carbonmonoxide/recognition.html Occupational Safety and Health Guideline for Carbon Monoxide]</ref>
<ref name=Blumenthal>Ivan Blumenthal (June 2001), &quot;Carbon monoxide poisoning&quot;, <i>Journal of the Royal Society of Medicine</i>, Vol. 94, Issue 6, pp.270-272, available online [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1281520/?tool=pmcentrez here].</ref>
<ref name=NationalAcademy>Committee on Medical and Biological Effects of Environmental Pollutants (1977), <i>Carbon Monoxide</i>, National Academy of Sciences, page 29, ISBN 0-309-02631-8.</ref>
<ref name=EPAiaq>[http://www.epa.gov/iaq/co.html An Introduction to Indoor Air Quality: Carbon Monoxide (CO)], U.S. Environmental Protection Agency (U.S. EPA).</ref>
<ref name=Gosink>Tom Gosink (1983), [http://www.gi.alaska.edu/ScienceForum/ASF5/588.html What Do Carbon Monoxide Levels Mean?], Alaska Science Forum, Geophysical Institute, University of Alaska.</ref>
<ref name=Thom>S.R. Thom (October, 2002), &quot;Hyperbaric-oxygen therapy for acute carbon monoxide poisoning&quot;, <i>New England Journal of Medicine</i>, Vol. 347, Issue 14, pp. 1105-1106.</ref>
<ref name=Ernst>Armin Ernst and Joseph D. Zibrak (November, 1998), &quot;Carbon monoxide poisoning&quot;, <i>New England Journal of Medicine</i>, Vol. 339, Issue 22, pp. 1603-1608.</ref>
<ref name=Heckerling>Paul S. Heckerling (May 1987), &quot;Occult carbon monoxide poisoning: a cause of winter headache&quot;, <i>American Journal of Emergency Medicine</i>, Vol. 5, Issue 3, pp. 201-204.</ref>
<ref name=Omaye>Stanley T. Omaye (November 2002), &quot;Metabolic modulation of carbon monoxide toxicity&quot;, <i>Toxicology</i>, Vol. 180, Issue 2, pp. 139-150.</ref>
<ref name=Hampson>Neil B. Hampson (September 1998), &quot;Emergency department visits for carbon monoxide poisoning in the Pacific Northwest&quot;, <i>Journal of Emergency Medicine</i>, Vol. 16, Issue 5, pp.695-698.</ref>
<ref name=CPSC>[http://www.cpsc.gov/CPSCPUB/PUBS/5010.html Carbon Monoxide, Detectors Can Save Lives, CPSC Document #5010], U.S. Consumer Product Safety Commission (CSPC).</ref>
<ref name=Cobb> Nathaniel Cobb and Ruth A. Etzel (August 1991), &quot;Unintentional carbon monoxide-related deaths in the United States, 1979 through 1988&quot;, <em>Journal of American Medical Association (JAMA</em>), Vol. 266, Issue 5, pp. 659&ndash;663.</ref>
<ref name=CDC>[http://www.cdc.gov/co/pdfs/faqs.pdf Carbon Monoxide Poisoning: Questions and Answers], Centers for Disease Control and Prevention (CDC).</ref>
<ref name=NYTimes>[http://www.nytimes.com/1993/01/26/science/carbon-monoxide-gas-is-used-by-brain-cells-as-a-neurotransmitter.html?pagewanted=1 Carbon Monoxide Gas Is Used by Brain Cells As a Neurotransmitter], Gina Kolata, New York Times article, January 26, 1993.</ref>
<ref name=LingLi>Ling Li, Anna Hsu and Philip K. Moore (2009), &quot;Actions and interactions of nitric oxide, carbon monoxide and hydrogen sulphide in the cardiovascular system and in inflammation--a tale of three gases!&quot;. <i>Pharmacology &amp; Therapeutics</i>, Vol. 123, Issue 3, pp. 386&ndash;400.</ref>
<ref name=BostonGlobe>[http://www.boston.com/news/local/massachusetts/articles/2009/10/16/poison_gas_may_carry_a_medical_benefit/?page=full Poison Gas May Carry a Medical Benefit], Carolyn Johnson, Boston Globe article, October 16, 2009.</ref>
<ref name=Oddvin>Oddvin S&oslash;rheim, Hilde Nissen and Truls Nesbakken (June 1999), &quot;The storage life of beef and pork packaged in an atmosphere with low carbon monoxide and high carbon dioxide&quot;, <i>Journal of Meat Science</i>, Vol. 52, Issue 2, pp. 157&ndash;164.</ref>
<ref name=Eilert>S.J. Eilert (September 2005), &quot;New packaging technologies for the 21st century&quot;, <i>Journal of Meat Science</i>, Vol. 71, Issue 1, pp. 122&ndash;127.</ref>
<ref name=FoodSafety>[http://www.foodsafetymagazine.com/article.asp?id=644&amp;sub=sub1 Low-Oxygen Packaging With CO: A Study in Food Politics That Warrants Peer Review], Randall D. Huffman and Janet M. Riley, Food Safety Magazine, Dec 2006/Jan 2007.</ref>
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Industrial air pollution source

Atmospheric dispersion modeling is the mathematical simulation of how air pollutants disperse in the ambient atmosphere. It is performed with computer programs that solve the mathematical equations and algorithms which simulate the pollutant dispersion. The dispersion models are used to estimate or to predict the downwind concentration of air pollutants emitted from sources such as industrial plants, vehicular traffic or accidental chemical releases.

Such models are important to governmental agencies tasked with protecting and managing the ambient air quality. The models are typically employed to determine whether existing or proposed new industrial facilities are or will be in compliance with the National Ambient Air Quality Standards (NAAQS) in the United States or similar regulations in other nations. The models also serve to assist in the design of effective control strategies to reduce emissions of harmful air pollutants. During the late 1960's, the Air Pollution Control Office of the U.S. Environmental Protection Agency (U.S. EPA) initiated research projects to develop models for use by urban and transportation planners.[1]

Air dispersion models are also used by emergency management personnel to develop emergency plans for accidental chemical releases. The results of dispersion modeling, using worst case accidental releases and meteorological conditions, can provide estimated locations of impacted areas and be used to determine appropriate protective actions. At industrial facilities in the United States, this type of consequence assessment or emergency planning is required under the Clean Air Act (CAA) codified in Part 68 of Title 40 of the Code of Federal Regulations.

The dispersion models vary depending on the mathematics used to develop the model, but all require the input of data that may include:

  • Meteorological conditions such as wind speed and direction, the amount of atmospheric turbulence (as characterized by what is called the "stability class"), the ambient air temperature, the height to the bottom of any inversion aloft that may be present, cloud cover and solar radiation.
  • The emission parameters such the type of source (i.e., point, line or area), the mass flow rate, the source location and height, the source exit velocity, and the source exit temperature.
  • Terrain elevations at the source location and at receptor locations, such as nearby homes, schools, businesses and hospitals.
  • The location, height and width of any obstructions (such as buildings or other structures) in the path of the emitted gaseous plume as well as the terrain surface roughness (which may be characterized by the more generic parameters "rural" or "city" terrain).

Many of the modern, advanced dispersion modeling programs include a pre-processor module for the input of meteorological and other data, and many also include a post-processor module for graphing the output data and/or plotting the area impacted by the air pollutants on maps. The plots of areas impacted usually include isopleths showing areas of pollutant concentrations that define areas of the highest health risk. The isopleths plots are useful in determining protective actions for the public and first responders.

The atmospheric dispersion models are also known as atmospheric diffusion models, air dispersion models, air quality models, and air pollution dispersion models.

Atmospheric layers

Discussion of the layers in the Earth's atmosphere is needed to understand where airborne pollutants disperse in the atmosphere. The layer closest to the Earth's surface is known as the troposphere. It extends from sea-level up to a height of about 18 km and contains about 80 percent of the mass of the overall atmosphere. The stratosphere is the next layer and extends from 18 km up to about 50 km. The third layer is the mesosphere which extends from 50 km up to about 80 km. There are other layers above 80 km, but they are insignificant with respect to atmospheric dispersion modeling.

The lowest part of the troposphere is called the atmospheric boundary layer (ABL) or the planetary boundary layer (PBL) and extends from the Earth's surface up to about 1.5 to 2.0 km in height. The air temperature of the atmospheric boundary layer decreases with increasing altitude until it reaches what is called the inversion layer (where the temperature increases with increasing altitude) that caps the atmospheric boundary layer. The upper part of the troposphere (i.e., above the inversion layer) is called the free troposphere and it extends up to the 18 km height of the troposphere.

The ABL is the most important layer with respect to the emission, transport and dispersion of airborne pollutants. The part of the ABL between the Earth's surface and the bottom of the inversion layer is known as the mixing layer. Almost all of the airborne pollutants emitted into the ambient atmosphere are transported and dispersed within the mixing layer. Some of the emissions penetrate the inversion layer and enter the free troposphere above the ABL.

In summary, the layers of the Earth's atmosphere from the surface of the ground upwards are: the ABL made up of the mixing layer capped by the inversion layer; the free troposphere; the stratosphere; the mesosphere and others. Many atmospheric dispersion models are referred to as boundary layer models because they mainly model air pollutant dispersion within the ABL. To avoid confusion, models referred to as mesoscale models have dispersion modeling capabilities that can extend horizontally as much as a few hundred kilometres. It does not mean that they model dispersion in the mesosphere.

Gaussian air pollutant dispersion equation

The technical literature on air pollution dispersion is quite extensive and dates back to the 1930s and earlier. One of the early air pollutant plume dispersion equations was derived by Bosanquet and Pearson.[2] Their equation did not assume Gaussian distribution nor did it include the effect of ground reflection of the pollutant plume.

Sir Graham Sutton derived an air pollutant plume dispersion equation in 1947[3][4] which did include the assumption of Gaussian distribution for the vertical and crosswind dispersion of the plume and also included the effect of ground reflection of the plume.

Under the stimulus provided by the advent of stringent environmental control regulations, there was an immense growth in the use of air pollutant plume dispersion calculations between the late 1960s and today. A great many computer programs for calculating the dispersion of air pollutant emissions were developed during that period of time and they were commonly called "air dispersion models". The basis for most of those models was the Complete Equation For Gaussian Dispersion Modeling Of Continuous, Buoyant Air Pollution Plumes shown below:[5][6]


where:  
= crosswind dispersion parameter
  =
= vertical dispersion parameter =
= vertical dispersion with no reflections
  =
= vertical dispersion for reflection from the ground
  =
= vertical dispersion for reflection from an inversion aloft
  =
           
           
           
= concentration of emissions, in g/m³, at any receptor located:
            x meters downwind from the emission source point
            y meters crosswind from the emission plume centerline
            z meters above ground level
= source pollutant emission rate, in g/s
= horizontal wind velocity along the plume centerline, m/s
= height of emission plume centerline above ground level, in m
= vertical standard deviation of the emission distribution, in m
= horizontal standard deviation of the emission distribution, in m
= height from ground level to bottom of the inversion aloft, in m
= the exponential function

The above equation not only includes upward reflection from the ground, it also includes downward reflection from the bottom of any inversion lid present in the atmosphere.

The sum of the four exponential terms in converges to a final value quite rapidly. For most cases, the summation of the series with m = 1, m = 2 and m = 3 will provide an adequate solution.

and are functions of the atmospheric stability class (i.e., a measure of the turbulence in the ambient atmosphere) and of the downwind distance to the receptor. The two most important variables affecting the degree of pollutant emission dispersion obtained are the height of the emission source point and the degree of atmospheric turbulence. The more turbulence, the better the degree of dispersion.

Whereas older models rely on stability classes for the determination of and , more recent models increasingly rely on Monin-Obukhov similarity theory to derive these parameters.

Briggs plume rise equations

The Gaussian air pollutant dispersion equation (discussed above) requires the input of H which is the pollutant plume's centerline height above ground level. H is the sum of Hs (the actual physical height of the pollutant plume's emission source point) plus ΔH (the plume rise due the plume's buoyancy).

Visualization of a buoyant Gaussian air pollutant dispersion plume

To determine ΔH, many if not most of the air dispersion models developed between the late 1960s and the early 2000s used what are known as "the Briggs equations." G.A. Briggs first published his plume rise observations and comparisons in 1965.[7] In 1968, at a symposium sponsored by CONCAWE (a Dutch organization), he compared many of the plume rise models then available in the literature.[8] In that same year, Briggs also wrote the section of the publication edited by Slade[9] dealing with the comparative analyses of plume rise models. That was followed in 1969 by his classical critical review of the entire plume rise literature,[10] in which he proposed a set of plume rise equations which have become widely known as "the Briggs equations". Subsequently, Briggs modified his 1969 plume rise equations in 1971 and in 1972.[11][12]

Briggs divided air pollution plumes into these four general categories:

  • Cold jet plumes in calm ambient air conditions
  • Cold jet plumes in windy ambient air conditions
  • Hot, buoyant plumes in calm ambient air conditions
  • Hot, buoyant plumes in windy ambient air conditions

Briggs considered the trajectory of cold jet plumes to be dominated by their initial velocity momentum, and the trajectory of hot, buoyant plumes to be dominated by their buoyant momentum to the extent that their initial velocity momentum was relatively unimportant. Although Briggs proposed plume rise equations for each of the above plume categories, it is important to emphasize that "the Briggs equations" which become widely used are those that he proposed for bent-over, hot buoyant plumes.

In general, Briggs's equations for bent-over, hot buoyant plumes are based on observations and data involving plumes from typical combustion sources such as the flue gas stacks from steam-generating boilers burning fossil fuels in large power plants. Therefore the stack exit velocities were probably in the range of 20 to 100 ft/s (6 to 30 m/s) with exit temperatures ranging from 250 to 500 °F (120 to 260 °C).

A logic diagram for using the Briggs equations[5] to obtain the plume rise trajectory of bent-over buoyant plumes is presented below:

BriggsLogic.png
where:  
Δh = plume rise, in m
F  = buoyancy factor, in m4s−3
x = downwind distance from plume source, in m
xf = downwind distance from plume source to point of maximum plume rise, in m
u = windspeed at actual stack height, in m/s
s  = stability parameter, in s−2

The above parameters used in the Briggs' equations are discussed in Beychok's book.[5]

References

  1. J.C. Fensterstock et al, "Reduction of air pollution potential through environmental planning", JAPCA, Vol. 21, No. 7, 1971.
  2. C.H. Bosanquet and J.L. Pearson, "The spread of smoke and gases from chimneys", Trans. Faraday Soc., 32:1249, 1936.
  3. O.G. Sutton, "The problem of diffusion in the lower atmosphere", QJRMS, 73:257, 1947.
  4. O.G. Sutton, "The theoretical distribution of airborne pollution from factory chimneys", QJRMS, 73:426, 1947.
  5. 5.0 5.1 5.2 M.R. Beychok (2005). Fundamentals Of Stack Gas Dispersion, 4th Edition. author-published. ISBN 0-9644588-0-2. .
  6. D. B. Turner (1994). Workbook of atmospheric dispersion estimates: an introduction to dispersion modeling, 2nd Edition. CRC Press. ISBN 1-56670-023-X. .
  7. G.A. Briggs, "A plume rise model compared with observations", JAPCA, 15:433–438, 1965.
  8. G.A. Briggs, "CONCAWE meeting: discussion of the comparative consequences of different plume rise formulas", Atmos. Envir., 2:228–232, 1968.
  9. D.H. Slade (editor), "Meteorology and atomic energy 1968", Air Resources Laboratory, U.S. Dept. of Commerce, 1968.
  10. G.A. Briggs, "Plume Rise", USAEC Critical Review Series, 1969.
  11. G.A. Briggs, "Some recent analyses of plume rise observation", Proc. Second Internat'l. Clean Air Congress, Academic Press, New York, 1971.
  12. G.A. Briggs, "Discussion: chimney plumes in neutral and stable surroundings", Atmos. Envir., 6:507–510, 1972.

Further reading

  • M.R. Beychok (2005). Fundamentals Of Stack Gas Dispersion, 4th Edition. author-published. ISBN 0-9644588-0-2. 
  • K.B. Schnelle and P.R. Dey (1999). Atmospheric Dispersion Modeling Compliance Guide, 1st Edition. McGraw-Hill Professional. ISBN 0-07-058059-6. 
  • D.B. Turner (1994). Workbook of Atmospheric Dispersion Estimates: An Introduction to Dispersion Modeling, 2nd Edition. CRC Press. ISBN 1-56670-023-X. 
  • S.P. Arya (1998). Air Pollution Meteorology and Dispersion, 1st Edition. Oxford University Press. ISBN 0-19-507398-3. 
  • R. Barrat (2001). Atmospheric Dispersion Modelling, 1st Edition. Earthscan Publications. ISBN 1-85383-642-7. 
  • S.R. Hanna and R.E. Britter (2002). Wind Flow and Vapor Cloud Dispersion at Industrial and Urban Sites, 1st Edition. Wiley-American Institute of Chemical Engineers. ISBN 0-8169-0863-X. 
  • P. Zannetti (1990). Air pollution modeling : theories, computational methods, and available software. Van Nostrand Reinhold. ISBN 0-442-30805-1.