question: What happens to smoke when it spreads through the air?
comment: Smoke is mostly unburnt fuel or ash. The output of fire is CO2, H20 and some CO. None of those produce ash. For example, you burn log, the log will have some moisture, various resins and oils, and wood fibers. Most of it will burn, but not all of it. Some of the minerals and other stuff will be left behind as ash, or small ash particles will float into the air and later settle down somewhere else. Some of the resins and oils will vaporize and later cool down and settle down elsewhere. If you look in the house or car of heavy smokers, you often see an oily haze on windows, or a yellowish tinge to white clothes. That's mostly the resins and (some claim nicotine) settling on stuff. Most of that is from the cooled unburnt oils & resins that settled down somewhere.
passages: Smoke particulates, like other aerosols, are categorized into three modes based on particle size:
  
  BULLET::::- nuclei mode, with geometric mean radius between 2.5–20 nm, likely forming by condensation of carbon moieties.
  
  BULLET::::- accumulation mode, ranging between 75–250 nm and formed by coagulation of nuclei mode particles
  
  BULLET::::- coarse mode, with particles in micrometer range
  
  Most of the smoke material is primarily in coarse particles. Those undergo rapid dry precipitation, and the smoke damage in more distant areas outside of the room where the fire occurs is therefore primarily mediated by the smaller particles.
   Many compounds can be associated with particulates; whether by being adsorbed on their surfaces, or by being dissolved in liquid droplets. Hydrogen chloride is well absorbed in the soot particles.
  
  Inert particulate matter can be disturbed and entrained into the smoke. Of particular concern are particles of asbestos.
  
  Deposited hot particles of radioactive fallout and bioaccumulated radioisotopes can be reintroduced into the atmosphere by wildfires and forest fires; this is a concern in e.g. the Zone of alienation containing contaminants from the Chernobyl disaster.
   Aerosol of particles beyond visible size is an early indicator of materials in a preignition stage of a fire.
  
  Burning of hydrogen-rich fuel produces water; this results in smoke containing droplets of water vapor. In absence of other color sources (nitrogen oxides, particulates...), such smoke is white and cloud-like.
  
  Smoke emissions may contain characteristic trace elements. Vanadium is present in emissions from oil fired power plants and refineries; oil plants also emit some nickel. Coal combustion produces emissions containing aluminium, arsenic, chromium, cobalt, copper, iron, mercury, selenium, and uranium.
   Wildfire smoke is composed primarily of carbon dioxide and water vapor. Other common smoke components present in lower concentrations are carbon monoxide, formaldehyde, acrolein, polyaromatic hydrocarbons, and benzene. Small particulates suspended in air which come in solid form or in liquid droplets are also present in smoke. 80 -90% of wildfire smoke, by mass, is within the fine particle size class of 2.5 micrometers in diameter or smaller.
   Smoke inhalation is the primary cause of death in victims of indoor fires. The smoke kills by a combination of thermal damage, poisoning and pulmonary irritation caused by carbon monoxide, hydrogen cyanide and other combustion products.
  
  Smoke is an aerosol (or mist) of solid particles and liquid droplets that are close to the ideal range of sizes for Mie scattering of visible light.
  
  Section::::Chemical composition.
  
  The composition of smoke depends on the nature of the burning fuel and the conditions of combustion.
   Section::::Release and reception.
   Section::::Production.
   However, air quality in Oregon degraded as plumes of smoke drifted northward instead of concentrating in the Central Valley.
  
  Section::::Smoke and air quality.:Spare the Air.
   Electrostatic precipitation. The smoke is passed through an array of metal tubes which contain suspended wires. A (huge) electrical potential is applied across the tubes and wires so that the smoke particles become charged and are attracted to the sides of the tubes. This method can over-read by capturing harmless condensates, or under-read due to the insulating effect of the smoke. However, it is the necessary method for assessing volumes of smoke too great to be forced through a filter, i.e., from bituminous coal.
   In the first scene from the first episode of season 4, Saul is at his workplace in a Nebraska Cinnabon. This scene is set in Omaha, but the scene was filmed in Albuquerque at the Cottonwood Mall.
  
  Section::::Reception.
   Section::::Chemicals used.
  
  Section::::Chemicals used.:Zinc chloride.
  
  Zinc chloride smoke is grey-white and consists of tiny particles of zinc chloride. The most common mixture for generating these is a zinc chloride smoke mixture (HC), consisting of hexachloroethane, grained aluminium and zinc oxide. The smoke consists of zinc chloride, zinc oxychlorides, and hydrochloric acid, which absorb the moisture in the air. The smoke also contains traces of organic chlorinated compounds, phosgene, carbon monoxide, and chlorine.
   The particles in tobacco smoke are liquid aerosol droplets (~ 20% water), with a mass median aerodynamic diameter (MMAD) that is submicrometer (and thus, fairly "lung-respirable" by humans). The droplets are present in high concentrations (some estimates are as high as 10 droplets per cm). Most cigarettes today contain a cigarette filter, which can reduce "tar" and nicotine smoke yields up to 50% by several different mechanisms, with an even greater removal rate for other classes of compounds (e.g., phenols).
   Section::::Reception.
   Section::::Remediation.:Clean Air Act.
  
  The worst recorded instance was the Great Smog of 1952, when 4,000 deaths were reported in the city over a couple of days, and a subsequent 8,000 related deaths, leading to the passage of the Clean Air Act 1956, which banned the use of coal for domestic fires in some urban areas. The overall death toll from that incident is now believed to be around 12,000.
  
  Section::::Cultural references.
   Second-hand smoke has been shown to produce more particulate-matter (PM) pollution than an idling low-emission diesel engine. In an experiment conducted by the Italian National Cancer Institute, three cigarettes were left smoldering, one after the other, in a 60 m³ garage with a limited air exchange. The cigarettes produced PM pollution exceeding outdoor limits, as well as PM concentrations up to 10-fold that of the idling engine.
   The visible particulate matter in such smokes is most commonly composed of carbon (soot). Other particulates may be composed of drops of condensed tar, or solid particles of ash. The presence of metals in the fuel yields particles of metal oxides. Particles of inorganic salts may also be formed, e.g. ammonium sulfate, ammonium nitrate, or sodium chloride. Inorganic salts present on the surface of the soot particles may make them hydrophilic. Many organic compounds, typically the aromatic hydrocarbons, may be also adsorbed on the surface of the solid particles. Metal oxides can be present when metal-containing fuels are burned, e.g. solid rocket fuels containing aluminium. Depleted uranium projectiles after impacting the target ignite, producing particles of uranium oxides. Magnetic particles, spherules of magnetite-like ferrous ferric oxide, are present in coal smoke; their increase in deposits after 1860 marks the beginning of the Industrial Revolution. (Magnetic iron oxide nanoparticles can be also produced in the smoke from meteorites burning in the atmosphere.) Magnetic remanence, recorded in the iron oxide particles, indicates the strength of Earth's magnetic field when they were cooled beyond their Curie temperature; this can be used to distinguish magnetic particles of terrestrial and meteoric origin. Fly ash is composed mainly of silica and calcium oxide. Cenospheres are present in smoke from liquid hydrocarbon fuels. Minute metal particles produced by abrasion can be present in engine smokes. Amorphous silica particles are present in smokes from burning silicones; small proportion of silicon nitride particles can be formed in fires with insufficient oxygen. The silica particles have about 10 nm size, clumped to 70-100 nm aggregates and further agglomerated to chains. Radioactive particles may be present due to traces of uranium, thorium, or other radionuclides in the fuel; hot particles can be present in case of fires during nuclear accidents (e.g. Chernobyl disaster) or nuclear war.
   Section::::Plot.:Main story.
   A exposure assessment study performed by the Lawrence Berkeley National lab found that 80% to 90% of combusted cigarette nicotine adsorbs into surfaces. It has been shown that deposited nicotine may desorb or resuspend from non-cleaned surfaces and adsorb or redeposit elsewhere, including previously cleaned surfaces.
   Cigarette smoke is a major modifiable risk factor for lung disease, heart disease, and many cancers. Smoke can also be a component of ambient air pollution due to the burning of coal in power plants, forest fires or other sources, although the concentration of pollutants in ambient air is typically much less than that in cigarette smoke. One day of exposure to PM2.5 at a concentration of 880 μg/m3, such as occurs in Beijing, China, is the equivalent of smoking one or two cigarettes in terms of particulate inhalation by weight. The analysis is complicated, however, by the fact that the organic compounds present in various ambient particulates may have a higher carcinogenicity than the compounds in cigarette smoke particulates. Secondhand tobacco smoke is the combination of both sidestream and mainstream smoke emissions from a burning tobacco product. These emissions contain more than 50 carcinogenic chemicals. According to the Surgeon General's 2006 report on the subject, "Short exposures to secondhand [tobacco] smoke can cause blood platelets to become stickier, damage the lining of blood vessels, decrease coronary flow velocity reserves, and reduce heart variability, potentially increasing the risk of a heart attack". The American Cancer Society lists "heart disease, lung infections, increased asthma attacks, middle ear infections, and low birth weight" as ramifications of smoker's emission.
   Smoke burns are burns that tend to be caused as a result of flash fires, both in house fires and in small chemical fires. These can be made to be more severe by a large presence of atmospheric humidity. These burns tend to occur at a temperature of about 121 °C / 250 °F. The heat is almost instantaneous and it is just hot enough to singe or burn off the tips of stray hairs, but mostly damage is mild. The heat produced by the burning substance is rarely hot enough to burn the skin. Normally, in situations where smoke burns are possible, the heat and quantity of smoke needed are rarely produced.
   Smoke damage to electronic equipment can be significantly more extensive than the fire itself. Cable fires are of special concern; low smoke zero halogen materials are preferable for cable insulation.
  
  When smoke comes into contact with the surface of any substance or structure, the chemicals contained in it are transferred to it. The corrosive properties of the chemicals cause the substance or structure to decompose at a rapid rate. Certain materials or structures absorb these chemicals, which is why clothing, unsealed surfaces, potable water, piping, wood, etc., are replaced in most cases of structural fires.
  
  Section::::Measurement.
   Examples:
  
  BULLET::::- Air pollution from a power plant flue gas stack in a large scale analysis of air pollution
  
  BULLET::::- Water pollution from an oil refinery wastewater discharge outlet in a large scale analysis of water pollution
  
  BULLET::::- Gas escaping from a pressurised pipe in a laboratory
  
  BULLET::::- Smoke is often released from point sources in a wind tunnel in order to create a plume of smoke which highlights the flow of the wind over an object
  
  BULLET::::- Smoke from a localised chemical fire can be blown in the wind to form a plume of pollution
  
  Section::::Pollution.
   Zinc chloride smoke is grey-white and consists of tiny particles of zinc chloride. The most common mixture for generating these is the zinc chloride smoke mixture (HC), consisting of hexachloroethane, grained aluminium and zinc oxide. The smoke consists of zinc chloride, zinc oxychlorides, and hydrochloric acid, which absorb the moisture in the air. The smoke also contains traces of organic chlorinated compounds, phosgene, carbon monoxide, and chlorine.
   Section::::Dangers.
  
  Smoke from oxygen-deprived fires contains a significant concentration of compounds that are flammable. A cloud of smoke, in contact with atmospheric oxygen, therefore has the potential of being ignited – either by another open flame in the area, or by its own temperature. This leads to effects like backdraft and flashover. Smoke inhalation is also a danger of smoke that can cause serious injury and death.
   A smoke "simulant", usually a glycol or glycerine mixed with distilled water, is vaporised and then condensed in free air to produce the distinctive smoke-like effect. The particles produced are on average 0.2-2.0 micrometres in diameter, meaning that the fog settles very slowly (and therefore has excellent longevity). This also means that residue and contamination is highly unlikely.
  
  Section::::Applications.
  