Editing Nuclear winter (section)

=== Aerosol removal timescale ===
[[File:SmokeCeilingInLochcarron.jpg|thumb|Smoke rising in [[Lochcarron]], [[Scotland]], is stopped by an overlying natural low-level inversion layer of warmer air (2006).]]
The exact timescale for how long this smoke remains, and thus how severely this smoke affects the climate once it reaches the stratosphere, is dependent on both chemical and physical removal processes.<ref name="babel.hathitrust.org" />

The most important physical removal mechanism is "[[Rainout (radioactivity)|rainout]]", both during the "fire-driven [[convection|convective]] column" phase, which produces "[[firestorm|black rain]]" near the fire site, and rainout after the [[Plume (hydrodynamics)|convective plume]]'s dispersal, where the smoke is no longer concentrated and thus "wet removal" is believed to be very efficient.{{sfn|Toon|Turco|Robock|Bardeen|2007|p=1994}} However, these efficient removal mechanisms in the troposphere are avoided in the [[Robock]] 2007 study, where solar heating is modeled to quickly loft the soot into the stratosphere, "detraining" or separating the darker soot particles from the fire clouds' whiter [[water condensation]].{{sfn|Toon|Turco|Robock|Bardeen|2007|pp=1994–1996}}

Once in the stratosphere, the [[Physics|physical]] removal mechanisms affecting the timescale of the soot particles' residence are how quickly the aerosol of soot collides and [[aerosol#coagulate|coagulates]] with other particles via [[Brownian motion]],<ref name="babel.hathitrust.org" />{{sfn|Toon|Turco|Robock|Bardeen|2007|pp=1997–1998}}<ref name="a.mpg.de">[http://www.atmosphere.mpg.de/enid/906c8d956939bb335e9b051e10f45223,0/2__Particles/-_Transformation_and_removal_296.html Transformation and removal] {{webarchive| url=https://web.archive.org/web/20110727031911/http://www.atmosphere.mpg.de/enid/906c8d956939bb335e9b051e10f45223,0/2__Particles/-_Transformation_and_removal_296.html |date=2011-07-27 }} J. Gourdeau, LaMP Clermont-Ferrand, France, March 12, 2003</ref> and falls out of the atmosphere via gravity-driven [[dry deposition]],<ref name="a.mpg.de" /> and the time it takes for the "[[Phoresis|phoretic effect]]" to move coagulated particles to a lower level in the atmosphere.<ref name="babel.hathitrust.org"/> Whether by coagulation or the phoretic effect, once the aerosol of smoke particles are at this lower atmospheric level, [[cloud seeding]] can begin, permitting [[precipitation (meteorology)|precipitation]] to wash the smoke aerosol out of the atmosphere by the [[wet deposition]] mechanism.

The [[Chemistry|chemical]] processes that affect the removal are dependent on the ability of [[atmospheric chemistry]] to [[oxidize]] the [[carbonaceous]] component of the smoke, via reactions with oxidative species such as [[ozone]] and [[nitrogen oxides]], both of which are found at all levels of the atmosphere,<ref>[http://www.atmosphere.mpg.de/enid/906c8d956939bb335e9b051e10f45223,0/4__Gases_in_the_atmosphere/-_Distribution___concentration__2__3tg.html Distribution & concentration (2)] {{webarchive| url=https://web.archive.org/web/20110727031921/http://www.atmosphere.mpg.de/enid/906c8d956939bb335e9b051e10f45223,0/4__Gases_in_the_atmosphere/-_Distribution___concentration__2__3tg.html |date=2011-07-27 }} Dr. Elmar Uherek – Max Planck Institute for Chemistry Mainz, April 6, 2004</ref><ref>{{harvnb|Toon|Turco|Robock|Bardeen|2007|p=1999}}. "At one time it was thought that carbonaceous aerosol might be consumed by reactions with ozone (Stephens et al., 1989) and other oxidants, reducing the lifetime of soot at stratospheric altitudes. However recent data shows that the reaction probability for such loss of soot is about 10^-11 so it is not an important process on times scales of several years (Kamm et al., 2004). A full simulation of stratospheric chemistry, along with additional laboratory studies, would be needed to evaluate the importance of these processes. Rate constants for a number of potentially important reactions are lacking."</ref> and which also occur at greater concentrations when air is heated to high temperatures.

Historical data on residence times of aerosols, albeit a [[atmospheric particulate matter|different mixture of aerosols]], in this case [[stratospheric sulfur aerosols]] and [[volcanic ash]] from [[megavolcano]] eruptions, appear to be in the one-to-two-year time scale,<ref>{{cite web |website=How Volcanoes Work |url=http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html |access-date=2011-04-15 |archive-url=https://web.archive.org/web/20110423214804/http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html| archive-date=2011-04-23|url-status=live|title=Climate Effect of Volcanic Eruptions}}</ref> however aerosol–atmosphere interactions are still poorly understood.<ref>{{cite web |author=Geerts |first=B. |title=Aerosols and climate |url=http://www-das.uwyo.edu/~geerts/cwx/notes/chap02/aerosol&climate.html |url-status=live |archive-url=https://web.archive.org/web/20190121203256/http://www-das.uwyo.edu/~geerts/cwx/notes/chap02/aerosol%26climate.html |archive-date=2019-01-21}}</ref><ref>{{cite web| url=http://gacp.giss.nasa.gov/|title=Global Aerosol Climatology Project| website=gacp.giss.nasa.gov |publisher=NASA |access-date=2011-04-15|url-status=live |archive-url=https://web.archive.org/web/20080523102619/http://gacp.giss.nasa.gov/|archive-date=2008-05-23}}</ref>