I have Ozone data from a ground-based station in µg/m3, but I need the Ozone in Dobson Units (DU) to further input in a software. What's the conversion equation for µg/m3 to DU, i.e.
1 µg/m3 = ?? DU
Thanks.
Hi Majid,
The two units are for different quantities! You can't relate them directly.
DU is a unit for vertically integrated columns: 1 DU = 2.6867 10^20 molecules.m-2. It is a column density. Or using the molar mass of ozone: 1 DU = 2.1415 10^4 µg(O3)/m2.
µg/m3 is a unit used for concentrations.You have to integrate vertically it order to get to a column. 1 µg/m3 over a layer of 1 km is 4.667 10^-2 DU. Or using more realistic figures for the troposphere 50 µg/m3 over a layer of 10 km is 23.3 DU.
Note that by convention in the air quality community, 1 µg/m3 = 0.5 ppbv (parts per billion in volume; 1 pbbv = 1 molecule of ozone per 10^9 molecule of air) and not the result of the standard formula which uses the ambient air temperature. And from ppb, you can also integrate vertically if you know the profile density of air.
Hi Majid,
The two units are for different quantities! You can't relate them directly.
DU is a unit for vertically integrated columns: 1 DU = 2.6867 10^20 molecules.m-2. It is a column density. Or using the molar mass of ozone: 1 DU = 2.1415 10^4 µg(O3)/m2.
µg/m3 is a unit used for concentrations.You have to integrate vertically it order to get to a column. 1 µg/m3 over a layer of 1 km is 4.667 10^-2 DU. Or using more realistic figures for the troposphere 50 µg/m3 over a layer of 10 km is 23.3 DU.
Note that by convention in the air quality community, 1 µg/m3 = 0.5 ppbv (parts per billion in volume; 1 pbbv = 1 molecule of ozone per 10^9 molecule of air) and not the result of the standard formula which uses the ambient air temperature. And from ppb, you can also integrate vertically if you know the profile density of air.
Hi Majid,
One DU is 2.69×10^16 ozone molecules per square centimetre, or 2.69×10^20 per square metre. This is 0.4462 millimoles of ozone per square metre, or approximately 1.25 ppb of the average total column of air.
What are the units of Dobson units. That is how is it defined as ug/m3? Then find the way to define the ozone or the Dobson in terms of the other. Simple
DU is the unit of the thickness of ozone layer.
While the concentration (by volume) will be measure by ppm , ppb or convert to ug/m3.
Dear Colleague -
NASA has a nice description and 'visualization' of Dobson unit use for assessment of the ozone layer:
http://ozonewatch.gsfc.nasa.gov/facts/dobson_SH.html
A derivation of Dobson unit from the ideal gas law is presented here:
https://en.wikipedia.org/wiki/Dobson_unit
FYI - the June 2016 article in Science reports on the recent evidence of 'healing' of the Antarctic ozone layer (DOI: 10.1126/science.aae0061):
http://science.sciencemag.org/content/early/2016/06/30/science.aae0061
Good luck with your research,
Jacek
http://ozonewatch.gsfc.nasa.gov/facts/dobson_SH.html
http://science.sciencemag.org/content/early/2016/06/30/science.aae0061
https://en.wikipedia.org/wiki/Dobson_unit
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