Editing Soot

{{short description|Product of incomplete combustion of hydrocarbons}}
{{Other uses}}
[[File:Diesel-smoke.jpg|thumb|Emission of soot in the [[exhaust gas]] of a large [[Diesel engine|diesel]] truck, without [[Diesel particulate filter|particle filters]]]]
{{Pollution sidebar|Air}}

'''Soot''' ({{IPAc-en|s|ʊ|t}} {{respell|suut}}) is a mass of impure [[Carbonaceous|carbon]] particles resulting from the incomplete [[combustion]] of [[hydrocarbon]]s.<ref name="modeling">{{cite journal |last1=Omidvarborna |title=Recent studies on soot modeling for diesel combustion |journal=Renewable and Sustainable Energy Reviews |volume=48 |pages=635–647 |doi=10.1016/j.rser.2015.04.019 |display-authors=et al |year=2015|bibcode=2015RSERv..48..635O }}</ref> Soot is considered a hazardous substance with carcinogenic properties.<ref>{{Cite book|title=Carbon Black| last=Kliment| first=Josef| publisher=Czech Association of Industrial Chemistry|year=2008|isbn=978-80-02-02004-2|location=Zlín}}</ref> Most broadly, the term includes all the particulate matter produced by this process, including [[black carbon]] and residual [[Pyrolysis|pyrolysed]] fuel particles such as [[coal]], [[cenosphere]]s, charred wood, and [[petroleum coke]] classified as [[Coke (fuel)|cokes]] or [[Char (chemistry)|char]]. It can include [[polycyclic aromatic hydrocarbons]] and heavy metals like mercury.<ref>{{Cite web|date=2020-09-13|title=Black Carbon: A Deadly Air Pollutant|url=https://nomoreplanet.com/black-carbon/|access-date=2020-11-01|website=NoMorePlanet.com|language=en-US|archive-date=2021-03-04|archive-url=https://web.archive.org/web/20210304185122/https://nomoreplanet.com/black-carbon/|url-status=dead}}</ref>

Soot causes various types of [[cancer]] and lung disease.<ref>
*{{Cite journal |last1 = Bond |first1 = T. C. |last2 = Doherty |first2 = S. J. |last3 = Fahey |first3 = D. W. |last4 = Forster |first4 = P. M. |last5 = Berntsen |first5 = T. |last6 = Deangelo |first6 = B. J. |last7 = Flanner |first7 = M. G. |last8 = Ghan |first8 = S. |last9 = Kärcher |first9 = B. |last10 = Koch |first10 = D. |last11 = Kinne |first11 = S. |last12 = Kondo |first12 = Y. |last13 = Quinn |first13 = P. K. |last14 = Sarofim |first14 = M. C. |last15 = Schultz |first15 = M. G. |last16 = Schulz |first16 = M. |last17 = Venkataraman |first17 = C. | last18 = Zhang |first18 = H. |last19 = Zhang |first19 = S. |last20 = Bellouin |first20 = N. |last21 = Guttikunda |first21 = S. K. |last22 = Hopke |first22 = P. K. |last23 = Jacobson |first23 = M. Z. |last24 = Kaiser |first24 = J. W. |last25 = Klimont |first25 = Z. |last26 = Lohmann |first26 = U. |last27 = Schwarz |first28 = D. |first29=T. |last30=Warren |first30=S. G. |last28=Shindell |last29=Storelvmo |first27=J. P. |title=Bounding the role of black carbon in the climate system: A scientific assessment |doi=10.1002/jgrd.50171 |journal=Journal of Geophysical Research: Atmospheres |volume=118 |issue=11 |pages=5380 |year=2013 
|bibcode = 2013JGRD..118.5380B |url = https://deepblue.lib.umich.edu/bitstream/2027.42/99106/1/jgrd50171.pdf |doi-access = free }}
*{{cite news |author=Juliet Eilperin |url=https://www.washingtonpost.com/national/health-science/black-carbon-ranks-as-second-biggest-human-cause-of-global-warming/2013/01/15/6d4e542a-5f2d-11e2-9940-6fc488f3fecd_story.html?tid=pm_pop |title=Black carbon ranks as second-biggest human cause of global warming |newspaper=The Washington Post |date=2013-11-26 |access-date=2013-12-04}}</ref>

==Terminology==
===Definition===
Among scientists, exact definitions for soot vary, depending partly on their field.<ref name ="Sipkens2023"/> For example, [[Atmospheric science|atmospheric scientists]] may use a different definition compared to [[Toxicology|toxicologists]]. Soot's definition can also vary across time, and from paper to paper even among scientists in the same field. A common feature of the definitions is that soot is composed largely of carbon based particles resulting from the incomplete burning  of [[hydrocarbon]]s or organic fuel such as wood. Some note that soot may be formed by other high temperature processes, not just by burning.<ref name ="Sipkens2023"/> Soot typically takes an [[aerosol]] form when first created. It tends to eventually settle onto surfaces, though some parts of it may be decomposed while still airborne. In some definitions, soot is defined purely as [[carbonaceous]] particles, but in others it is defined to include the whole ensemble of particles resulting from partial combustion of [[organic matter]] or [[fossil fuels]] - as such it can include non carbon elements like [[Sulfur|sulphur]] and even traces of metal. In many definitions, soot is assumed to be black, but in some definitions it can be composed partly or even mainly of [[brown carbon]], and so can also be medium or even light gray in colour.<ref name ="Sipkens2023">{{cite journal | author = Sipkens ''et all'' | title =Overview of methods to characterize the mass, size, and morphology of soot | journal = [[Journal of Aerosol Science]] | volume = 173| pages =  | date = 2023| pmid = | doi =10.1016/j.jaerosci.2023.106211  | bibcode =2023JAerS.17306211S | doi-access = free}}</ref><ref name="Rituraj2017">{{cite journal | vauthors = Rituraj N , Kumar TA | title =The Toxicological Mechanisms of Environmental Soot (Black Carbon) and Carbon Black: Focus on Oxidative Stress and Inflammatory Pathways | journal = [[Frontiers in Immunology]] | volume =8 | date =2017  | page =763 | pmid = 28713383| doi =10.3389/fimmu.2017.00763  | doi-access =free | pmc =5492873 }}</ref><ref name = "Petzold2013">{{cite journal | author = Petzold ''et all''  | title = Recommendations for reporting "black carbon" measurements | journal = [[Atmospheric Chemistry and Physics]] | volume =13 | pages =  8365–8379| date =2013  | issue = 16 | pmid = | doi =10.5194/acp-13-8365-2013  | doi-access = free | bibcode = 2013ACP....13.8365P | hdl = 20.500.11850/71581 | hdl-access = free }}</ref><ref name = "long2013">{{cite journal | vauthors = Long CM, Nascarella MA, Valberg PA | title = Carbon black vs. black carbon and other airborne materials containing elemental carbon: physical and chemical distinctions| journal = [[Environmental Pollution (journal)|Environmental Pollution]] | volume =181 | pages =  271–286| date = 2013 | pmid = 23850403| doi =10.1016/j.envpol.2013.06.009 | bibcode = 2013EPoll.181..271L|quote = "the terms carbon black and soot have often been used interchangeably ...   other terms like soot, elemental carbon, and graphitic carbon continue to be used synonymously with black carbon"
| doi-access = free}}</ref>

===Related terms===
Terms like "soot", "carbon black", and "black carbon" are often used to mean the same thing, even in the scientific literature, but other scientists have stated this is incorrect and that they refer to chemically and physically distinct things.<ref name = "long2013"/><ref name="Rituraj2017"/><ref name = "Watson2001">{{cite journal | vauthors = Watson AY, Valberg PA  | title = Carbon black and soot: two different substances | journal = [[Journal of Occupational and Environmental Hygiene]] | volume =62 | pages =  218–228| date =2001  | issue = 2 | pmid = 11331994| doi = 10.1080/15298660108984625 }}</ref>

'''[[Carbon black]]''' is a term for the industrial production of powdery carbonaceous matter which has been underway since the 19th century. Carbon black is composed almost entirely of elemental carbon. Carbon black is not found in regular soot - only in the special soot that is intentionally produced for its manufacture, mostly from specialised oil furnaces.<ref name = "long2013"/><ref name="Rituraj2017"/>

'''[[Black carbon]]''' is a term that arose in the late twentieth century among atmospheric scientists, to describe strongly light absorbing carbonaceous particles which have a significant [[climate forcing]] affect - second only to {{CO2}} itself as a contributor to short term global warming. The term is sometimes used synonymously with soot, but is now used preferentially in atmospheric science, though some prefer more precise terms like 'light-absorbing carbon'.<ref>{{cite journal | author=[[Tami Bond]] |author2=Robert W. Bergstrom| date=2020-09-13|title=Light Absorption by Carbonaceous Particles: An Investigative Review|journal=Aerosol Science and Technology |volume=40 |pages=27–67 |doi=10.1080/02786820500421521|url=https://www.tandfonline.com/doi/pdf/10.1080/02786820500421521}}</ref> Unlike carbon black, black carbon is produced unintentionally. The chemical composition of ''black carbon'' is much more varied, and typically has a much lower proportion of elemental carbon, compared with ''carbon black''.<ref name = "long2013"/><ref name="Rituraj2017"/> In some definitions, black carbon also includes [[charcoal]], a type of matter where the chunks tend to be too large to have an aerosol form as is the case with soot.<ref>{{cite journal | vauthors = Burke M, Marín-Spiotta E, Ponette-González AG | title =Black carbon in urban soils: land use and climate drive variation at the surface. | journal = [[Carbon Balance and Management]] | volume =9 | date =2024  | issue =1 | page =9 | pmid = 38429441| doi =10.1186/s13021-024-00255-3  | doi-access =free | pmc =10908174 | bibcode =2024CarBM..19....9B }}</ref>

== Sources ==
Soot as an airborne contaminant in the environment has many different sources, all of which are results of some form of [[pyrolysis]]. They include soot from [[coal]] burning, internal-combustion engines,<ref name="modeling"/> power-plant boilers, hog-fuel boilers, ship boilers, central steam-heat boilers, [[waste incineration]], local field burning, house fires, forest fires, fireplaces, and furnaces. These exterior sources also contribute to the indoor environment sources such as smoking of plant matter, cooking, [[oil lamp]]s, [[candle]]s, quartz/halogen bulbs with settled dust, [[fireplace]]s, exhaust emissions from vehicles,<ref name="b20">{{cite journal|last1=Omidvarborna|title=Characterization of particulate matter emitted from transit buses fueled with B20 in idle modes|journal=Journal of Environmental Chemical Engineering|volume=2|issue=4|pages=2335–2342|doi=10.1016/j.jece.2014.09.020|display-authors=etal|year=2014}}</ref> and defective furnaces. Soot in very low concentrations is capable of darkening surfaces or making particle agglomerates, such as those from ventilation systems, appear [[black carbon|black]]. Soot is the primary cause of "ghosting", the discoloration of walls and ceilings or walls and flooring where they meet. It is generally responsible for the discoloration of the walls above baseboard [[electric heating]] units.

The formation and properties of soot depend strongly on the fuel composition, but may also be influenced by flame temperature.<ref>{{cite book |last1=Seinfeld |first1=John H. |last2=Pandis |first2=Spyros N. |title=Atmospheric Chemistry and Physics : From Air Pollution to Climate Change |edition=2nd |publisher=John Wiley & Sons |year=2006 |isbn=0-471-72018-6 }}</ref><ref>{{Cite journal |last1=Alfè |first1=M. |last2=Apicella |first2=B. |last3=Rouzaud |first3=J.-N. |last4=Tregrossi |first4=A. |last5=Ciajolo |first5=A. |date=October 2010 |title=The effect of temperature on soot properties in premixed methane flames |url=https://linkinghub.elsevier.com/retrieve/pii/S0010218010000374 |journal=Combustion and Flame |language=en |volume=157 |issue=10 |pages=1959–1965 |doi=10.1016/j.combustflame.2010.02.007|bibcode=2010CoFl..157.1959A }}</ref> Regarding fuel composition, the rank ordering of sooting tendency of fuel components is:{{clarify|date=September 2024}} [[naphthalenes]] → [[benzenes]] → [[aliphatics]].{{citation needed|date=September 2024}} However, the order of sooting tendencies of the aliphatics ([[alkanes]], [[alkenes]], and [[alkynes]]) varies dramatically depending on the flame type. The difference between the sooting tendencies of aliphatics and aromatics is thought to result mainly from the different routes of formation. Aliphatics appear to first form acetylene and polyacetylenes, which is a slow process; aromatics can form soot both by this route and also by a more direct pathway involving ring condensation or polymerization reactions building on the existing aromatic structure.<ref>{{cite journal |last1=Graham |first1=S. C. |last2=Homer |first2=J. B. |last3=Rosenfeld |first3=J. L. J. |year=1975 |jstor=78961 |title=The formation and coagulation of soot aerosols generated in pyrolysis of aromatic hydrocarbons |journal=Proc. R. Soc. Lond. A |volume=344 |pages=259–285 |doi=10.1098/rspa.1975.0101 |s2cid=96742040 }}</ref><ref>{{cite book |last1=Flagan |first1=R. C. |last2=Seinfeld |first2=J. H. |year=1988 |title=Fundamentals of Air Pollution Engineering |publisher=Prentice-Hall |location=Englewood Cliffs, NJ |isbn=0-13-332537-7 }}</ref>

== Description ==
The [[Intergovernmental Panel on Climate Change]] (IPCC) adopted the description of soot particles given in the glossary of Charlson and Heintzenberg (1995), "Particles formed during the quenching of gases at the outer edge of flames of organic vapours, consisting predominantly of carbon, with lesser amounts of oxygen and hydrogen present as carboxyl and phenolic groups and exhibiting an imperfect graphitic structure".<ref>{{cite book |editor-last=Charlson |editor-first=R. J. |editor2-last=Heintzenberg |editor2-first=J. |year=1995 |title=Aerosol Forcing of Climate |publisher=John Wiley & Sons |location=New York, NY |page=406 |isbn=0-471-95693-7 }}</ref>

Formation of soot is a complex process, an evolution of matter in which a number of molecules undergo many chemical and physical reactions within a few milliseconds.<ref name="modeling"/> Soot always contains nanoparticles of graphite and diamond, a phenomenon known as gemmy soot. Soot is a powder-like form of [[amorphous carbon]]. Gas-phase soot contains [[polycyclic aromatic hydrocarbon]]s (PAHs).<ref name="modeling"/><ref>Rundel, Ruthann, "Polycyclic Aromatic Hydrocarbons, Phthalates, and Phenols", in Indoor Air Quality Handbook, John Spengleer, Jonathan M. Samet, John F. McCarthy (eds), pp. 34.1-34.2, 2001</ref> The PAHs in soot are known [[mutagens]]<ref>Rundel, Ruthann, "Polycyclic Aromatic Hydrocarbons, Phthalates, and Phenols", in Indoor Air Quality Handbook, John Spengleer, Jonathan M. Samet, John F. McCarthy (eds), pp. 34.18-34.21, 2001</ref> and are classified as a "known human [[carcinogen]]" by the [[International Agency for Research on Cancer]] (IARC).<ref>{{cite web|url=https://www.inchem.org/documents/iarc/vol35/soots.html |title=Soots (IARC Summary & Evaluation, Volume 35, 1985) |publisher=Inchem.org |date=1998-04-20 |access-date=2013-12-04}}</ref> Soot forms during incomplete combustion from precursor molecules such as acetylene. It consists of agglomerated [[nanoparticle]]s with diameters between 6 and 30&nbsp;[[nanometre|nm]]. The soot particles can be mixed with metal oxides and with minerals and can be coated with [[sulfuric acid]].<ref name="modeling"/><ref name=Niessner>{{cite journal |last=Niessner |first=R. |year=2014 |title=The Many Faces of Soot: Characterization of Soot Nanoparticles Produced by Engines |journal=Angew. Chem. Int. Ed. |volume=53 |issue= 46|pages=12366–12379 |doi=10.1002/anie.201402812 |pmid=25196472 }}</ref>

==Soot formation mechanism==
Many details of soot formation chemistry remain unanswered and controversial, but there have been a few agreements:<ref name="modeling"/>
* Soot begins with some [[precursor (chemistry)|precursor]]s or building blocks.
* [[Nucleation]] of heavy molecules occurs to form particles.
* Surface growth of a particle proceeds by adsorption of gas phase molecules.
* [[Coagulation]] happens via reactive particle–particle collisions.
* [[Oxidation]] of the molecules and soot particles reduces soot formation.

==Hazards==
[[File:MML43083 at Nottingham 2005-10-14 03.jpg|thumb|right|The black staining on the power car of this [[Midland Mainline (train operating company)|Midland Mainline]] [[InterCity 125]] High Speed Train is the result of soot building up on the train's surface.]]
Soot, particularly [[diesel exhaust]] pollution, accounts for over one-quarter of the total hazardous pollution in the air.<ref name="b20"/><ref>{{cite web |url=http://www.nctcog.org/trans/air/vehicles/health.asp |title=Health Concerns Associated with Excessive Idling |publisher=Nctcog.org |access-date=2013-12-04 |archive-date=2014-01-16 |archive-url=https://web.archive.org/web/20140116215922/http://www.nctcog.org/trans/air/vehicles/health.asp |url-status=dead }}</ref>

Among these [[Diesel fuel|diesel]] emission components, [[particulates|particulate matter]] has been a serious concern for human health due to its direct and broad impact on the respiratory organs. In earlier times, health professionals associated [[Particulates#Size, shape and solubility matter|PM]]<sub>10</sub> (diameter < 10&nbsp;[[μm]]) with chronic lung disease, [[lung cancer]], [[influenza]], [[asthma]], and increased [[mortality rate]]. However, recent scientific studies suggest that these correlations be more closely linked with fine particles (PM<sub>2.5</sub>) and ultra-fine particles (PM<sub>0.1</sub>).<ref name="modeling"/>

Long-term [[Exposure to toxins|exposure]] to [[urban air pollution]] containing soot increases the risk of [[coronary artery disease]].<ref>[http://content.nejm.org/cgi/content/full/356/5/447 "Long-Term Exposure to Air Pollution and Incidence of Cardiovascular Events in Women"] {{Webarchive|url=https://web.archive.org/web/20070202183626/http://content.nejm.org/cgi/content/full/356/5/447 |date=2007-02-02 }} Kristin A. Miller, David S. Siscovick, [[Lianne Sheppard]], Kristen Shepherd, Jeffrey H. Sullivan, Garnet L. Anderson, and Joel D. Kaufman, in ''[[New England Journal of Medicine]]'' February 1, 2007</ref>

Diesel [[Exhaust gas|exhaust]] (DE) gas is a major contributor to [[combustion]]-derived particulate-matter air pollution.<ref name="b20"/> In human experimental studies using an exposure chamber setup, DE has been linked to [[Acute toxicity|acute]] [[Blood vessel|vascular]] [[Abnormality (behavior)|dysfunction]] and increased [[thrombus]] formation.<ref>{{cite journal |title=Diesel exhaust inhalation increases thrombus formation in man |first1=Andrew J. |last1=Lucking |first2=Magnus |last2=Lundback |first3=Nicholas L. |last3=Mills |first4=Dana |last4=Faratian |first5=Stefan L. |last5=Barath |first6=Jamshid |last6=Pourazar |first7=Flemming R. |last7=Cassee |first8=Kenneth |last8=Donaldson |first9=Nicholas A. |last9=Boon |first10=Juan J. |last10=Badimon |first11=Thomas |last11=Sandström |first12=Anders |last12=Blomberg |first13=David E. |last13=Newby |display-authors=1 |journal=European Heart Journal |volume=29 |issue=24 |year=2008 |pages=3043–3051 |doi=10.1093/eurheartj/ehn464 |doi-access=free |pmid=18952612 }}</ref><ref>{{cite journal |title=Persistent Endothelial Dysfunction in Humans after Diesel Exhaust Inhalation |first1=Håkan |last1=Törnqvist |first2=Nicholas L. |last2=Mills |first3=Manuel |last3=Gonzalez |first4=Mark R. |last4=Miller |first5=Simon D. |last5=Robinson |first6=Ian L. |last6=Megson |first7=William |last7=MacNee |first8=Ken |last8=Donaldson |first9=Stefan |last9=Söderberg |first10=David E. |last10=Newby |first11=Thomas |last11=Sandström |first12=Anders |last12=Blomberg |display-authors=1 |journal=American Journal of Respiratory and Critical Care Medicine |volume=176 |issue=4 |year=2007 |doi=10.1164/rccm.200606-872OC |pmid=17446340 |pages=395–400 }}</ref> This serves as a plausible mechanistic link between the previously described association between particulate matter air pollution and increased cardiovascular morbidity and mortality.

Soot also tends to form in [[chimney]]s in domestic houses possessing one or more [[fireplace]]s. If a large deposit collects in one, it can ignite and create a [[chimney fire]]. Regular cleaning by a [[chimney sweep]] should eliminate the problem.<ref>{{Cite web|date=2015-02-22|title=Gr8fires|url=https://blog.gr8fires.co.uk/2015/02/22/how-to-remove-soot-from-a-chimney/|website=gr8fires.co.uk}}</ref>

==Soot modeling==
Soot mechanism is difficult to model mathematically because of the large number of primary components of [[diesel fuel]], complex combustion mechanisms, and the [[heterogeneous]] interactions during soot formation.<ref name="modeling"/> Soot models are broadly categorized into three subgroups: empirical (equations that are adjusted to match experimental soot profiles), semi-empirical (combined mathematical equations and some empirical models which used for particle number density and soot volume and mass fraction), and detailed theoretical mechanisms (covers detailed chemical kinetics and physical models in all phases).<ref name="modeling"/>

First, empirical models use correlations of experimental data to predict trends in soot production. Empirical models are easy to implement and provide excellent correlations for a given set of operating conditions. However, empirical models cannot be used to investigate the underlying mechanisms of soot production. Therefore, these models are not flexible enough to handle changes in operating conditions. They are only useful for testing previously established designed experiments under specific conditions.<ref name="modeling"/>

Second, semi-empirical models solve rate equations that are calibrated using experimental data. Semi-empirical models reduce computational costs primarily by simplifying the chemistry in soot formation and oxidation. Semi-empirical models reduce the size of chemical mechanisms and use simpler molecules, such as acetylene as precursors.<ref name="modeling"/>
Detailed theoretical models use extensive chemical mechanisms containing hundreds of [[chemical reactions]] in order to predict concentrations of soot. Detailed theoretical soot models contain all the components present in the soot formation with a high level of detailed chemical and physical processes.<ref name="modeling"/>

Finally, comprehensive models (detailed models) are usually expensive and slow to compute, as they are much more complex than empirical or semi-empirical models. Thanks to recent technological progress in computation, it has become more feasible to use detailed theoretical models and obtain more realistic results; however, further advancement of comprehensive theoretical models is limited by the accuracy of modeling of formation mechanisms.<ref name="modeling"/>

Additionally, [[phenomenological model]]s have found wide use recently. Phenomenological soot models, which may be categorized as semi-empirical models, correlate empirically observed phenomena in a way that is consistent with the fundamental theory, but is not directly derived from the theory. These models use sub-models developed to describe the different processes (or phenomena) observed during the combustion process. Examples of sub-models of phenomenological empirical models include spray model, lift-off model, heat release model, ignition delay model, etc. These sub-models can be empirically developed from observation or by using basic physical and chemical relations. Phenomenological models are accurate for their relative simplicity. They are useful, especially when the accuracy of the model parameters is low. Unlike empirical models, phenomenological models are flexible enough to produce reasonable results when multiple operating conditions change.<ref name="modeling"/>

==Applications==
Historically soot was used in manufacturing artistic paints and [[shoe polish]], as well as a blackener for [[Russia leather]] for boots. With the advent of the [[printing press]] it was used in the printing ink well into the 20th century.<ref>Surmiński, Janusz, "Węglarstwo leśne – sadza i potaż", Sylwan vol. 154 (3), 2010, pp.  182−186 (pdf file: <!-- [https://bibliotekanauki.pl/ bibliotekanauki.pl] is blacklisted in wikipedia--> www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjD_-mOqOCCAxWzKEQIHc-7BIIQFnoECBcQAQ&url=https%3A%2F%2Fbibliotekanauki.pl%2Farticles%2F1009503.pdf&usg=AOvVaw0K6o-KjiJN4ULbJqxQdDNx&opi=89978449)</ref>

==See also==
{{Div col|colwidth=20em}}
*[[Activated carbon]]
*[[Atmospheric particulate matter]]
*[[Bistre]]
*[[Black carbon]]
*[[Carbon black]]
*[[Coal]]
*[[Colorant]]
*[[Creosote#Build-up in chimneys|Creosote]]
*[[Diesel particulate matter]]
*[[Dust]]
*[[Fullerene]]
*[[Health effects of coal ash]]
*[[Health effects of wood smoke]]
*[[Indian ink]]
*[[Joss paper]]
*[[Open burning of waste]]
*[[Rolling coal]]
*[[Soot blower]]
*[[Spheroidal carbonaceous particles]]
*[[Sulfur dioxide]]
{{Div col end}}

==References==
{{Reflist|2}}

==External links==
{{commons category}}
* {{Cite Americana|wstitle=Blacks |short=x}}

{{Pollution}}

[[Category:Allotropes of carbon]]
[[Category:IARC Group 1 carcinogens]]
[[Category:Pollution]]
[[Category:Air pollution]]