Editing Aerosol (section)

=== Effects ===
{{See also|Particulates#Climate effects}}
[[File:20231206 Radiative forcing (warming influence) - global warming.svg |thumb|Aerosols have a cooling effect that is small compared to the radiative forcing (warming effect) of greenhouse gases.<ref name=ESSD_2022>{{cite journal |last1=Forster |first1=Piers M. |last2=Smith |first2=Christopher J. |last3=Walsh |first3=Tristram |last4=Lamb |first4=William F. |last5=Lamboll |first5=Robin |display-authors=4 |title=Indicators of Global Climate Change 2022: annual update of large-scale indicators of the state of the climate system and human influence |url=https://essd.copernicus.org/articles/15/2295/2023/essd-15-2295-2023.pdf |journal=Earth System Science Data |date=2023 |volume=15 |issue=6 |pages=2295–2327 |publisher=Copernicus Programme |doi=10.5194/essd-15-2295-2023 |bibcode=2023ESSD...15.2295F |doi-access=free }} Fig. 2(a).</ref>]]
[[File:1750- Radiative forcing - greenhouse gases and aerosols.svg|thumb| Hansen ''et{{nbsp}}al.'' (2025) wrote that the IPCC had underestimated aerosols' cooling effect, causing it to also underestimate [[climate sensitivity]] (Earth's responsiveness to increases in greenhouse gas concentrations).<ref name=Envt_Hanson_20250203/> In what Hansen called a [[Deal with the Devil|Faustian bargain]], regulation of aerosols improved air quality, but aerosols' cooling effect became inadequate to temper the increasing warming effect of greenhouse gases—explaining unexpectedly large global warming in 2023-2024.<ref name=Envt_Hanson_20250203>{{cite journal |last1=Hansen |first1=James E. |last2=Kharecha |first2=Pushker |last3=Sato |first3=Makiko |last4=Tselioudis |first4=George |last5=Kelly |first5=Joseph |last6=Bauer |first6=Susanne E. |last7=Ruedy |first7=Reto |last8=Jeong |first8=Eunbi |last9=Jin |first9=Quijian |last10=Rignot |first10=Eric |last11=Velicogna |first11=Isabella |last12=Schoeberl |first12=Mark R. |last13=von Schuckmann |first13=Karina |last14=Amponsem |first14=Joshua |last15=Cao |first15=Junji |last16=Keskinen |first16=Anton |last17=Li |first17=Jing |last18=Pokela |first18=Anni |display-authors=4 |title=Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed? |journal=Environment |date=3 February 2025 |volume=67 |issue=1 |pages=6-44 |doi=10.1080/00139157.2025.2434494|doi-access=free }} Figure 3.</ref>]]

Volcanic eruptions release large amounts of [[sulphuric acid]], [[hydrogen sulfide]] and [[hydrochloric acid]] into the atmosphere. These gases represent aerosols and eventually return to earth as [[acid rain]], having a number of [[Acid rain#Adverse effects|adverse effects]] on the environment and human life.<ref name="nasa">
{{cite web |last1=Allen |first1=Bob |title=Atmospheric Aerosols: What Are They, and Why Are They So Important? |url=http://www.nasa.gov/centers/langley/news/factsheets/Aerosols.html |access-date=8 July 2014 |website=NASA }}</ref>

When aerosols absorb pollutants, it facilitates the deposition of pollutants to the surface of the earth as well as to bodies of water.<ref name="kommalapati" /> This has the potential to be damaging to both the environment and human health.

Aerosols interact with the [[Earth's energy budget]] in two ways, directly and indirectly.
:* E.g., a ''direct'' effect is that aerosols scatter and absorb incoming solar radiation.<ref>{{Cite web |last=Highwood |first=Ellie |date=2018-09-05 |title=Aerosols and Climate |url=https://www.rmets.org/resource/aerosols-and-climate |access-date=2019-10-07 |website=Royal Meteorological Society |language=en}}</ref> This will mainly lead to a cooling of the surface (solar radiation is scattered back to space) but may also contribute to a warming of the surface (caused by the absorption of incoming solar energy).<ref>{{Cite web |title=Fifth Assessment Report - Climate Change 2013 |url=https://www.ipcc.ch/report/ar5/wg1/ |access-date=2018-02-07 |website=www.ipcc.ch}}</ref> This will be an additional element to the [[greenhouse effect]] and therefore contributing to the global climate change.<ref name="kommalapati">{{cite book |last1=Kommalapati |first1=Raghava R. |title=Atmospheric aerosols: Characterization, chemistry, modeling, and climate |last2=Valsaraj |first2=Kalliat T. |date=2009 |publisher=American Chemical Society |isbn=978-0-8412-2482-7 |volume=1005 |location=Washington, DC |pages=1–10 |doi=10.1021/bk-2009-1005.ch001}}</ref>
:* The ''indirect'' effects refer to the aerosol interfering with formations that interact directly with radiation. For example, they are able to modify the size of the cloud particles in the lower atmosphere, thereby changing the way clouds reflect and absorb light and therefore modifying the Earth's energy budget.<ref name="nasa" />
:* There is evidence to suggest that anthropogenic aerosols actually offset the effects of greenhouse gases in some areas, which is why the Northern Hemisphere shows slower surface warming than the Southern Hemisphere, although that just means that the Northern Hemisphere will absorb the heat later through ocean currents bringing warmer waters from the South.<ref>Anthropogenic Aerosols, Greenhouse Gases, and the Uptake, Transport, and Storage of Excess Heat in the Climate System {{cite journal |last1=Irving |first1=D. B. |last2=Wijffels |first2=S. |last3=Church |first3=J. A. |year=2019 |title=Anthropogenic Aerosols, Greenhouse Gases, and the Uptake, Transport, and Storage of Excess Heat in the Climate System |journal=Geophysical Research Letters |volume=46 |issue=9 |pages=4894–4903 |bibcode=2019GeoRL..46.4894I |doi=10.1029/2019GL082015 |doi-access=free|hdl=1912/24327 |hdl-access=free }}</ref> On a global scale however, aerosol cooling decreases greenhouse-gases-induced heating without offsetting it completely.<ref>GIEC AR6 WG1 - Figure SPM.2 https://www.ipcc.ch/report/sixth-assessment-report-working-group-i/</ref>
[[Ship tracks]] are [[cloud]]s that form around the [[Exhaust gas|exhaust]] released by ships into the still ocean air. Water [[molecule]]s collect around the tiny particles ([[Particulate|aerosols]]) from exhaust to form a [[cloud seed]]. More and more water accumulates on the seed until a visible cloud is formed. In the case of ship tracks, the cloud seeds are stretched over a long narrow path where the wind has blown the ship's exhaust, so the resulting clouds resemble long strings over the ocean.<ref>{{Cite web |last=Wellock |first=Bill |date=2024-01-17 |title=Changing the sky: FSU researchers examine how aerosols from ships affect cloud formation, climate change |url=https://news.fsu.edu/news/science-technology/2024/01/17/changing-the-sky-fsu-researchers-examine-how-aerosols-from-ships-affect-cloud-formation-global-warming/ |access-date=2024-07-15 |website=Florida State University News |language=en-US}}</ref>

The warming caused by human-produced greenhouse gases has been somewhat offset by the cooling effect of human-produced aerosols. In 2020, regulations on fuel significantly cut [[sulfur dioxide]] emissions from international shipping by approximately 80%, leading to an unexpected global geoengineering termination shock.<ref name=":1">{{Cite journal |last1=Yuan |first1=Tianle |last2=Song |first2=Hua |last3=Oreopoulos |first3=Lazaros |last4=Wood |first4=Robert |last5=Bian |first5=Huisheng |last6=Breen |first6=Katherine |last7=Chin |first7=Mian |last8=Yu |first8=Hongbin |last9=Barahona |first9=Donifan |last10=Meyer |first10=Kerry |last11=Platnick |first11=Steven |date=2024-05-30 |title=Abrupt reduction in shipping emission as an inadvertent geoengineering termination shock produces substantial radiative warming |journal=Communications Earth & Environment |language=en |volume=5 |issue=1 |page=281 |doi=10.1038/s43247-024-01442-3 |issn=2662-4435 |pmc=11139642 |pmid=38826490|bibcode=2024ComEE...5..281Y }}</ref>

Aerosols in the 20&nbsp;μm range show a particularly long persistence time in air conditioned rooms due to their "jet rider" behaviour (move with air jets, gravitationally fall out in slowly moving air);<ref>{{Cite medRxiv |medrxiv=10.1101/2020.12.08.20233056v1 |first=Patrick |last=Hunziker |title=Minimizing exposure to respiratory droplets, 'jet riders' and aerosols in air-conditioned hospital rooms by a 'Shield-and-Sink' strategy |date=2020-12-16 |language=en}}</ref> as this aerosol size is most effectively adsorbed in the human nose,<ref>{{Cite journal |last1=Kesavanathan |first1=Jana |last2=Swift |first2=David L. |year=1998 |title=Human Nasal Passage Particle Deposition: The Effect of Particle Size, Flow Rate, and Anatomical Factors |journal=Aerosol Science and Technology |volume=28 |issue=5 |pages=457–463 |bibcode=1998AerST..28..457K |doi=10.1080/02786829808965537 |issn=0278-6826}}</ref> the primordial infection site in [[COVID-19]], such aerosols may contribute to the pandemic.<ref name="McNeill">{{cite journal |vauthors=McNeill VF |date=June 2022 |title=Airborne Transmission of SARS-CoV-2: Evidence and Implications for Engineering Controls |journal=Annual Review of Chemical and Biomolecular Engineering |volume=13 |issue=1 |pages=123–140 |doi=10.1146/annurev-chembioeng-092220-111631 |pmid=35300517 |s2cid=247520571}}</ref>

Aerosol particles with an effective diameter smaller than 10&nbsp;μm can enter the bronchi, while the ones with an effective diameter smaller than 2.5&nbsp;μm can enter as far as the gas exchange region in the lungs,<ref name="volcanic_emissions">
{{cite web |last1=Grainger |first1=Don |title=Volcanic Emissions |url=http://eodg.atm.ox.ac.uk/eodg/research_ve.html |access-date=8 July 2014 |website=Earth Observation Data Group, Department of Physics, University of Oxford |publisher=University of Oxford}}</ref> which can be hazardous to human health.