Editing Trace gas (section)

== Abundance, sources and sinks ==
The abundance of a trace gas can range from a few parts per trillion ([[Parts-per notation|ppt]]) by volume to several hundred parts per million by volume ([[Parts-per notation|ppmv]]).<ref name=":0">{{Cite book|title=Atmospheric Science: An Introductory Survey|last1=Wallace|first1=John|last2=Hobbs|first2=Peter|publisher=Elsevier Academic Press|year=2006|isbn=9780127329512|location=Amsterdam, Boston}}</ref> When a trace gas is added into the atmosphere, that process is called a ''source''. There are two possible types of sources - natural or anthropogenic. Natural sources are caused by processes that occur in nature. In contrast, anthropogenic sources are caused by human activity.

Some sources of a trace gas are [[Biogenic substance|biogenic]] processes, [[outgassing]] from solid Earth, ocean emissions, industrial emissions, and [[in situ]] formation.<ref name=":0" /> A few examples of biogenic sources include [[photosynthesis]], [[Manure|animal excrements]], [[termite]]s, [[Paddy field|rice paddies]], and [[wetland]]s. Volcanoes are the main source for trace gases from solid earth. The global [[ocean]] is also a source of several trace gases, in particular sulfur-containing gases. In situ trace gas formation occurs through chemical reactions in the gas-phase.<ref name=":0" /> Anthropogenic sources are caused by human related activities such as fossil fuel combustion (e.g. in [[transportation]]), fossil fuel mining, [[biomass burning]], and industrial activity.

In contrast, a ''sink'' is when a trace gas is removed from the atmosphere. Some of the sinks of trace gases are chemical reactions in the atmosphere, mainly with the [[Hydroxyl radical|OH radical]], gas-to-particle conversion forming [[aerosols]], [[wet deposition]] and [[dry deposition]].<ref name=":0" /> Other sinks include microbiological activity in soils.

Below is a chart of several trace gases including their abundances, atmospheric lifetimes, sources, and sinks. &nbsp;

'''Trace gases – taken at pressure 1 atm'''<ref name=":0" /> 
{| class="wikitable"
!'''Gas'''
!'''Chemical formula'''
!'''Fraction of volume of air by the species'''
!'''Residence time or lifetime'''
!'''Major sources'''
!'''Major sinks'''
|-
|[[Carbon dioxide]]
|CO<sub>2</sub>
|419 [[Parts-per notation|ppm]] ≈ppmv<br>(May, 2021)<ref>{{cite web |url=https://gml.noaa.gov/ccgg/trends/ |title=Trends in Atmospheric Carbon Dioxide |publisher=NOAA Earth System Research Laboratories |access-date=2022-01-20}}</ref>
|Increasing,<br>See Note{{ref label|COL|A|A}}
|Biological, oceanic, combustion, anthropogenic
|photosynthesis
|-
|[[Neon]]
|Ne
|18.18 ppmv
|_________
|Volcanic
|________
|-
|[[Helium]]
|He
|5.24 ppmv
|_________
|Radiogenic
|________
|-
|[[Methane]]
|CH<sub>4</sub>
|1.89 ppm<br>(May, 2021)<ref>{{cite web |url=https://gml.noaa.gov/ccgg/trends_ch4/ |title=Trends in Atmospheric Methane |publisher=NOAA Earth System Research Laboratories |access-date=2022-01-20}}</ref>
|9 years
|Biological, anthropogenic
|OH
|-
|[[Hydrogen]]
|H<sub>2</sub>
|0.56 ppmv
|~ 2 years
|Biological, HCHO [[photodissociation|photolysis]]
|soil uptake
|-
|[[Nitrous oxide]]
|N<sub>2</sub>O
|0.33 ppmv
|150 years
|Biological, anthropogenic
|O(<sup>1</sup>D) in stratosphere
|-
|[[Carbon monoxide]]
|CO
|40 – 200 ppbv
|~ 60 days
|Photochemical, combustion, anthropogenic
|OH
|-
|[[Ozone]]
|O<sub>3</sub>
|10 – 200 ppbv (troposphere)
|Days – months
|Photochemical
|photolysis
|-
|[[Formaldehyde]]
|HCHO
|0.1 – 10 ppbv
|~ 1.5 hours
|Photochemical
|OH, photolysis
|-
|[[NOx|Nitrogen species]]
|NO<sub>x</sub>
|10 pptv – 1 ppmv
|Variable
|Soils, anthropogenic, lightning
|OH
|-
|[[Ammonia]]
|NH<sub>3</sub>
|10 pptv – 1 ppbv
|2 – 10 days
|Biological
|gas-to-particle conversion
|-
|[[Sulfur dioxide]]
|SO<sub>2</sub>
|10 pptv – 1 ppbv
|Days
|Photochemical, volcanic, anthropogenic
|OH, water-based oxidation
|-
|[[Dimethyl sulfide]]
|(CH<sub>3</sub>)<sub>2</sub>S
|several pptv – several ppbv
|Days
|Biological, ocean
|OH
|}
{{note label|COL|A|A}} The [[Intergovernmental Panel on Climate Change]] (IPCC) states that ''"no single atmospheric lifetime can be given"'' for CO<sub>2</sub>.<ref name="ar5">{{cite book |url=https://www.ipcc.ch/report/ar5/wg1/ |contribution= Chapter 8 |title=AR5 Climate Change 2013: The Physical Science Basis}}</ref>{{rp|731}}  This is mostly due to the high rate of growth and large cumulative magnitude of the disturbances to Earth's [[carbon cycle]] by the geologic extraction and burning of fossil carbon.<ref>Friedlingstein, P., Jones, M., O'Sullivan, M., Andrew, R., Hauck, J., Peters, G., Peters, W., Pongratz, J., Sitch, S., Le Quéré, C. and 66 others (2019) "Global carbon budget 2019". ''Earth System Science Data'', '''11'''(4): 1783–1838. {{doi|10.5194/essd-11-1783-2019}}</ref>  As of year 2014, fossil CO<sub>2</sub> emitted as a theoretical 10 to 100&nbsp;GtC pulse on top of the existing atmospheric concentration was expected to be 50% removed by land vegetation and ocean [[carbon sink|sinks]] in less than about a century.<ref>{{cite book|title=Intergovernmental Panel on Climate Change Fifth Assessment Report - Supplemental Material |chapter-url=https://www.ipcc.ch/site/assets/uploads/2018/07/WGI_AR5.Chap_.8_SM.pdf |chapter=Figure 8.SM.4|page=8SM-16}}</ref> A substantial fraction (20-35%) was also projected to remain in the atmosphere for centuries to millennia, where fractional persistence increases with pulse size.<ref>{{cite journal |last= Archer |first= David |title= Atmospheric lifetime of fossil fuel carbon dioxide |journal= Annual Review of Earth and Planetary Sciences |volume= 37 |pages= 117–34 |year= 2009 |issue= 1 |doi= 10.1146/annurev.earth.031208.100206| bibcode =  2009AREPS..37..117A |hdl= 2268/12933 |url= https://orbi.uliege.be/handle/2268/12933}}</ref><ref>{{Cite journal |url=https://www.atmos-chem-phys.net/13/2793/2013/ |author=Joos, F. |author2=Roth, R. |author3=Fuglestvedt, J.D. |display-authors=etal |year=2013 |title=Carbon dioxide and climate impulse response functions for the computation of greenhouse gas metrics: A multi-model analysis |journal=Atmospheric Chemistry and Physics |volume=13 |issue=5 |pages=2793–2825 |doi=10.5194/acpd-12-19799-2012|doi-access=free |hdl=20.500.11850/58316 |hdl-access=free }}</ref>  Thus CO<sub>2</sub> lifetime effectively increases as more fossil carbon is extracted by humans.