When we use AMS or ACSM, the term 'non-refractory' is assigned to species that evaporate rapidly at 600 °C under vacuum conditions (e.g. organic matter, NH4NO3 and (NH4)2SO4. And regarding refractory aerosol components, which is not high enough to efficiently vaporize at 600 °C, usually include sea salt, many mineral oxides, elemental carbon (soot) and metals.
I want know what refractory organic aerosol is? Does it even exist? I think so, but could you give an example of their chemical composition?
Hi Guoliang,
I always thought that this was a methodological definition. Carbon particulates that are oxidized up to about 600ºC (note that last time I checked there was no standard method) were classified as organic carbon and the rest, that required oxidizing gas, catalysts and higher temperature, were classified as elemental carbon. For me, this is also the distinction between non-refractory and refractory carbon. A few years back I remember reading an interesting article discussing the nature of the EC and comparing with other methodological definitions, as the BC - I think it was from professor Tami Bond.
Best,
Hi Alexandre, thanks for your information.
It seems that some studies try to differentiate non-refractory OC and refractory OC using OCEC instrument (Sunset)with IMPROVE protocol, which which produced four OC fractions in a non-oxidizing He atmosphere (OC1, OC2, OC3, and OC4 at temperatures of 120, 250, 450, and 550 ◦C, respectively); while others differentiate them using Aerosol mass spectrometry (AMS).
I once read a paper titled 'Absorption and scattering properties of organic carbon versus sulfate dominant aerosols at Gosan climate observatory in Northeast Asia'. The author regards OC3 and OC4 as the refractory OC.
Thank you Gouliang for the follow up; I was unaware of this use. It seems than that you have a good methodological definition of what would be an refractory organic carbon aerosol, and at least one paper using this definition, which partially answer your question. I hope someone can help you with the chemical nature of such compounds.
Best,
Alexandra
I do not understand what you mean with
"Carbon particulates that are OXIDISED up to about 600ºC were classified as organic carbon":
at this temperature all carbon is combusted:
did you mean HEATED up to 600 C without OXYGEN?
Gouliang
Protocols: the IMPROVE protocol is just one; there is also the NIOSH DRI and EUSAAR protocol in which the heating rates are different and thus also the various fractions OC1 OC2 etc
Hi, Dear Harry ,
Thank you for your helpful supplement. So it's necessary to mention the protocol when trying to distinguish OC1 OC2 etc.
Regards,
Alexandre
{I apologize for an earlier typo in your name)
As for the 600C: the problem is that part of the OC shows pyrolysis and turns into amorphic elemental carbon. For that reason there is the optical correction for this extra EC in the so-called TOT / TOR methods used to distinguish OC and EC
Cite
Khan M. G. Mostofa
Tianjin University
Dear Guoliang,
I read all answers, but I did not get clear. When you are burned the refractory organic substances, which is mostly humic substances, which is composed of humic acid and fulvic acid. They are also found in water significantly. When they are heated up to 600 degree C, they are mostly oxidized to CO2 in the presence of O2. This is very common. On the other hand, elemental analyser can produce the elemental carbon that is mentioned by Prof. Harry.
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Guoliang Li
City University of Hong Kong
Hi, Dr. Khan,
It may be the two different instuments (AMS and OCEC analyzer) that make you coffused.
It's clear now when we use OCEC, we can differentiate non-refractory OC and refractory OC a certain protocol, which produced several OC fractions in a non-oxidizing He atmosphere (e.g. OC1, OC2, OC3, and OC4 at temperatures of 120, 250, 450, and 550 ◦C, respectively);
When we use AMS or its brother ACSM, there is also no oxygen in the vaporizer, 'cause it's a high vacuum system there. The non-refractory species can vaporize instantly. Whlie the refractory species may not. That's just what I asked in this question. In these refractory species, will there be any organics? This confused me for a long time. Now I tend to think that almost all organics would be vaporized in the high vacuum system at 600 ℃.
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Conor A Nixon
NASA
I would suspect that PAHs (e.g. soot) would be a major component of organic, refractory aerosol.
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Harry ten Brink
ECN part of TNO
Conor
Soot contain only a minor fraction of PAHs. Soot is a very ill defined term describing particulate matter that is produced in incomplete combustion of diesel, wood and other combustible material. Its chemical composition is very loosely known because the organic condensed fraction ha a high molecular weight and therefore not analyzable
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M.M. Sarin
Physical Research Laboratory
The concept of refractory and/or non-refractory organic aerosols is not strictly correct. It depends on the analytical protocol. On EC-OC analyser, particulate matter combusted at 600 deg C is treated as organic carbon (OC).
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Harry ten Brink
ECN part of TNO
Conor
"Soot" is very ill defined and a bulk name for the particulates emitted in incomplete combustion of fuels like diesel or candles. Its composition is largely unknown because to be in the condensed phase the components have to have very low vapour pressure which in turn means a high molecular weight. This makes it difficult for chemical speciation. Actually, half of the diesel soot is refractory ELEMENTAL carbon as proven by electron microscopy (Sarofim and cow) substantiated by Raman spectroscopic analysis. The elemental carbon units of several tens of nanometer consist of rounded crystalline graphitic structures.
The percentage PAHs in soot as far as analysed is low
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1 Recommendation
Harry ten Brink
ECN part of TNO
Conor
Apologies for the second entry of mine: the first was not visible to me for almost a day and I thought something had gone wrong with the upload; hence the second try
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Robert Frantisek Holub
Clarkson University
It's better to think in terms of "stickiness" (van der Waals, intermolecular, physical forces), which are omnipresent, regardless of what mixture of chemical substances it happens to be (in the absence of reactions caused by direct sunlight). All substances stick, even He. In view of the enormous amount of chemicals in air, some less some more sticky, these admixtures cannot be meaningfully defined as volatile, semi-volatile, refractory etc. In addition, the stickiness is the key criterion for the efficiency of the cloud condensation nuclei (CCN) in forming clouds and rain, the key uncertainty in all climate models. Harry sent me once a paper, cited 88 x, "Aerosols before pollution" by Andreae M O (thanks). Yet I'm not convinced. In mid-continents there must have been some extra sticky aerosols (not HULIS, - humic-like substances), more like the sea salt or so, to make rains occur. Back to the question - if a HULIS aerosol contains say 10% of the extra sticky substance, equally distributed, it will behave as refractory. At, say 1%, as a semi-volatile, etc..If anybody wants to discuss this further, my email is [email protected]
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1 Recommendation
Guoliang Li
City University of Hong Kong
Hi, Corbin,
Having gone through your answer, very beneficial!
Thank you
Lane
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Harry ten Brink
ECN part of TNO
Joel
According to my info the mentioned functional groups are a surface layer at the surface of the "soot" the inner-core is a graphitic like layered sphere (Sarofim et al.)
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Harry ten Brink
ECN part of TNO
Guoliang
Replying to an earlier entry by you: you think that in the AMS all "OC" will vaporize. I am not so sure. In combustion there is the a similar question how much of the material vaporizes. There is seen that it depends on the heating rate which also depends on the size of the sample (for instance combustion of pulverised coal)
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1 Recommendation
Guoliang Li
City University of Hong Kong
Hi, Dear Harry,
What you said really makes sense. We should be more careful when we deal with the relevant data. More possibilities should be considered. Thank you for your beneficial info.
Guoliang
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1 Recommendation
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