Hi,
first of all, I am very pleased to see this topic getting more and more attention in this newsgroup and also in the community of (atmospheric) chemistry modellers. It is good to have people like Christiane and Philip involved in this and I hope that we will be more in the future when more people realize the advantages of some standards for exchanging and assessing multiple output.
Concerning the list of chemical names, I don't think that CAS or any list with similar level of detail is the way forward. While most models treat a certain number of species (typically 40-60) explicitely, they always group organic species into compound classes in order to make the problem solvable (you just cannot imagine a global or regional 3D model with several million chemical variables). Yes - there are box models which go a certain way to treat individual compounds and radical species (for example the Master Chemical Mechanism in the UK or NCAR's master mechanism), but even these don't resolve everything after a certain point.
Luckily, the community is usually interested in a small subset of species only. Presumably the list compiled by Christiane covers quite a bit of that already. However, it is unavoidable to also consider "lumped" compounds in for example intercomparison studies. Then the difficulty is to find an unambiguous definition which nevertheless encompasses a sufficiently large number of models so that the "standard" is not only a private convention which could even interfere with other similar definitions. Let me give two examples here:
(1) pentanes: chemically, one distinguishes between n-pentane and i-pentane (one is linear the other molecule "T"-shaped). Both react through different pathways and form different compounds in the end. Nevertheless, the two molecules are practically always grouped together in modelling applications and the different reaction pathways are described via stochiometric factors
pentane + OH -> 0.7 * X + 0.3 * Y + 0.235 * Z + ...
In this example, defining a standard name for pentane would pose no major problem, I suppose.
(2) alkanes: Many models treat alkanes explicitly up to a certain C-number (usually 3, 4, or 5) and then lump everything else together. Practically, one could of course define standard names such as
mixing_ratio_of_alkanes_with_at_least_three_c_atoms_in_air
mixing_ratio_of_alkanes_with_at_least_four_c_atoms_in_air
mixing_ratio_of_alkanes_with_at_least_five_c_atoms_in_air
mixing_ratio_of_alkanes_with_at_least_six_c_atoms_in_air
...
However, the rule to make use of these would be quite complex. Say, you want to compute the total amount of hydrocarbons in an air mass, then this would be either
ethane + alkanes(C3) + "aromatics" + ...
or
ethane + propane + alkanes(C4) + "aromatics" + ...
or
ethane + propane + butane + alkanes(C5) + "aromatics" + ...
...
And the same complications (if not worse) appear with unsaturated species, oxygenated species, etc.
I don't know an easy way out of this, but it is good that these things are discussed here and now.
Best regards,
Martin
< Dr. Martin G. Schultz, ICG-II, Forschungszentrum J?lich >
< D-52425 J?lich, Germany >
< ph: +49 (0)2461 61 2831, fax: +49 (0)2461 61 8131 >
< email: m.schultz at fz-juelich.de >
< web:
http://www.fz-juelich.de/icg/icg-2/m_schultz >
Forschungszentrum J?lich GmbH
52425 J?lich
Sitz der Gesellschaft: J?lich
Eingetragen im Handelsregister des Amtsgerichts D?ren Nr. HR B 3498
Vorsitzende des Aufsichtsrats: MinDirig'in B?rbel Brumme-Bothe
Vorstand: Prof. Dr. Achim Bachem (Vorsitzender), Dr. Ulrich Krafft (stellv.
Vorsitzender)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Martin Schultz (m.schultz at fz-juelich.de).vcf
Type: text/x-vcard
Size: 481 bytes
Desc: Martin Schultz (m.schultz at fz-juelich.de).vcf
URL: <
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/attachments/20070806/7bea8961/attachment-0002.vcf>
Received on Mon Aug 06 2007 - 02:40:16 BST
