In my opinion, the UV-carbon is always greater than BC (880nm), as the manual say, "If sampling a ‘normal’ aerosol, this ‘UV’ result will be closely equal to the ‘BC’ result. If sampling an aerosol that has a strong “blue” component (e.g. fresh diesel exhaust or tobacco smoke), then this ‘UV’ result will be substantially larger than the ‘BC’ result.".
But recently I read one paper titled "Absorption and scattering properties of organic carbon versus sulfate dominant aerosols at Gosan climate observatory in Northeast Asia" pubulished on ACP, the author seperated the data into two groups (370nm and 880 nm), based on the observed maxima daily-averaged value in 370nm and 880nm. That is, the author observed a greater value in 880nm than that in 370nm, which really confused me. I have read the paper several times, and I think I didn't misinterpret what the author's expressing.
http://www.atmos-chem-phys.net/14/7781/2014/
Hi, Jorge,
Thanks for your reply. Maybe you missed the column of table 1 for 880 group. Pls find the attached screenshot.
And I agree with your opinion that "The fact that mass concentrations at 880 nm reported by the AE are sometimes higher than those ones at 370 nm is just the product of a calculation made by the AE software and it is based on a particular wavelength dependence which does not always fits the real aerosol properties. "
Actually, we have encountered this phenomenon once (that UV-carbon < BC-880), and we contacted Magee's engineer. After clean the optical chamber and other maintenance as they told us, the AE33 became "normal" (UV-carbon > BC-880) again. So that's why I am confused by that publication.
Thanks,
Guoliang Li
Dear Harry,
As I mentioned, I have read this paper for several times. I didn't think I misundertand this publication. Otherwise I won't ask a quesion here before thinking.
Thanks,
Guoliang Li
Hi, Jorge,
I agree. The absorption coefficients at 370n are surely higher than that at 880nm, if not, the machine must be broken, I think.
In my opinion, it would be better for the author to calculate the ratio of Abs(370) and Abs(880), and compared the ratio with 880/370 (i.e., 2.38) for grouping. Since it would reflect some info on wavelength dependence.
Thanks,
Guoliang
Guoliang
fair enough; you did your homework
best way is to give feedback is to communicate directly with the authors
Dear Ariadne,
Thanks for your information. I have read the reports.
Notice that it's said in your report that "The UV component concentration is obtained by subtracting the measured BC concentration from the concentration measured by the 370nm source.The UV component is not a real physical or chemical material, but a parameter based on UV absorption due to the mix of organic compounds measured at this wavelength. This fictional material ‘UVPM’ is expressed in units of ‘BC Equivalent."
What I mean here the UV-carbon (370nm) is UVPM which was directly available from Aethalometer, also, the publication I mentioned in the question use the term EBC (370nm), the same as UVPM.
So your reports actually support my opinion, that is, only the "UVPM" is greater than BC (880nm), can you get positive value by substract the measured BC concentration (you call it UV component, this value is reasonably smaller than BC-880nm).
Thanks,
Guoliang Li
Dear Harry,
Thanks for your suggestion. I have sent email to the author.
For now, I'm more confident that it's due to uncertainty of measurment with Aethalometer. That is, when the sampling aerosol has many organic compounds, which could absorb more UV photons, the EBC (370nm) will be obviously greater than EBC (880); But instead, when the sampling aerosol has a little or little organic compounds, the greater EBC (370) value may not be that obvious, maybe close to EBC (880nm), even smaller than that at 880nm, as the author observed.
Note: EBC is short for equivalent black carbon. Here in this discussion, EBC (370nm) = UV-carbon (370nm) = UVPM; EBC(880nm) = BC (880nm)
Thanks,
Guoliang Li
Dear Harry,
I know Dr. Petzold has one publication titled "Recommendations for reporting "black carbon" measurements". didn't know which one do you mean. could you please send the title?
Thanks,
Guoliang
Exactly he discusses there the different parameters for EC/BC/LAC and thus EBC
He has the longest history in EC/BC (in Europe) thus THE expert in this area. He also is the inventor of the MAAP
Yes, I just read his papers again and feel very informative.
Many thanks to your patient and helpful instruction, Harry.
Thanks,
Guoliang
Dear all,
Here is the author's reply as attached.
He mentioned that "our grouping (i.e., 370 nm group vs 880 nm group) should be accepted in a relative way to stress two cases, (i) samples having components that absorb relatively more light at short wavelength and (ii) samples having components that absorb relatively more light at longer wavelength."
Well, I didn't think of any other components that will absorb more long-wavelength (880nm) light than Black carbon. In my opinion, if the sample is pure BC, EBC(370) will be equal to EBC (880) (see attached pic), but once there is organics that absorb UV-light, EBC(370) will be greater than EBC (880).
Best,
Guoliang
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