Question
Asked 12th Jul, 2016

How to convert Ozone units from µg/m3 to Dobson Unit?

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.

Most recent answer

14th Jul, 2016
Jacek A Koziel
United States Department of Agriculture
Dear Colleague -
NASA has a nice description and 'visualization' of Dobson unit use for assessment of the ozone layer:
A derivation of Dobson unit from the ideal gas law is presented here:
FYI - the June 2016 article in Science reports on the recent evidence of 'healing' of the Antarctic ozone layer (DOI: 10.1126/science.aae0061):
Good luck with your research,
Jacek
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Popular Answers (1)

13th Jul, 2016
Vincent-Henri Peuch
European Center For Medium Range Weather Forecasts
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.
11 Recommendations

All Answers (5)

13th Jul, 2016
Vincent-Henri Peuch
European Center For Medium Range Weather Forecasts
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.
11 Recommendations
13th Jul, 2016
Borys Buznytskyi
National Taras Shevchenko University of Kyiv
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.
1 Recommendation
13th Jul, 2016
James Argo
IntrAmericas Centre for Environment and Health
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
14th Jul, 2016
Kanita Thanacharoenchanaphas
Naresuan University
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.

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