Editing Dobson unit (section)

{{Short description|Measurement of equivalent thickness of atmospheric trace gas}}
The '''Dobson unit''' (DU) is a unit of measurement of the amount of a trace gas in a vertical column through the [[Earth's atmosphere]]. It originated by, and continues to be primarily used in respect to, the study of atmospheric [[ozone]], whose total column amount, usually termed "total ozone", and sometimes "column abundance", is dominated by the high concentrations of ozone in the [[stratospheric]] [[ozone layer]].

The Dobson unit is defined as the thickness (in units of 10&nbsp;μm) of that layer of pure gas which would be formed by the total column amount at [[standard conditions for temperature and pressure]] (STP).<ref>{{cite web|url=https://ozonewatch.gsfc.nasa.gov/facts/dobson_SH.html|title=Ozone Hole Watch: Facts About Dobson Units}}</ref><ref>{{GoldBookRef|title=Dobson unit ''in atmospheric chemistry''|file=D01827}}</ref> This is sometimes referred to as a 'milli-atmo-centimeter'. A typical column amount of 300&nbsp;DU of atmospheric ozone therefore would form a 3&nbsp;mm layer of pure gas at the surface of the Earth if its temperature and pressure conformed to STP.

The Dobson unit is named after [[Gordon Dobson]], a researcher at the [[University of Oxford]] who in the 1920s built the first instrument to measure total ozone from the ground, making use of a double prism [[monochromator]] to measure the differential absorption of different bands of solar ultraviolet radiation by the ozone layer. This instrument, called the [[Dobson ozone spectrophotometer]], has formed the backbone of the global network for monitoring atmospheric ozone<ref>{{cite journal |last1=Staehelin |first1=Johannes |title=Global atmospheric ozone monitoring |journal=WMO Bulletin |date=2008 |volume=57 |issue=1 |url=https://public-old.wmo.int/en/bulletin/global-atmospheric-ozone-monitoring|archive-url=https://web.archive.org/web/20231218180609/https://public-old.wmo.int/en/bulletin/global-atmospheric-ozone-monitoring|url-status=dead|archive-date=December 18, 2023}}</ref> and was the source of the discovery in 1984 of the [[Antarctic ozone hole]].<ref>{{cite journal |last1=Farman |first1=J. C. |last2=Gardiner |first2=B. G. |last3=Shankin |first3=J. D. |year=1985 |title=Large losses of total ozone in Antarctica reveal seasonal ClO<sub>x</sub>/NO<sub>x</sub> interaction |journal=Nature |volume=315 |issue=16 May 1985 |pages=207–210 |doi=10.1038/315207a0|bibcode=1985Natur.315..207F }}</ref>