[CF-metadata] standard names for chemistry - MCM

From: Philip J. Cameronsmith1 <cameronsmith1>
Date: Thu, 23 Oct 2008 13:09:55 -0700 (PDT)

Hi Martin, et al.

You are correct, of course, about X, A, G, and why we have both
mass_fraction_of_, mole_fraction_of_, and _expressed_as_. I'm sorry
if this was not clear from my email.

The reason for bringing all this up is that we are proposing an important
change to the way standard names are handled, and I suspect that many
people want to be sure this is as simple and clean as possible.

This is why I was trying to point out that CF doesn't need to keep
separate lists for X, A, G, or any other set of species. We will only
need a single list of species: X.

We then have two choices: (i) force all quantities with species in X to
use the same units; or (ii) allow all possible units for all species in X,
so that the user can decide what makes most sense for any given specie,
with the knowledge that the units can be easily converted if needed (as
long as the molar mass is known).

It appears that you (Martin) and Jonathan prefer option (ii), and I agree,
even though it will mean a slightly larger list of standard names. :-)

Yours truly,

       Philip


On Thu, 23 Oct 2008, Schultz, Martin wrote:

> On Wed, 22 Oct 2008 13:00:47 -0700 (PDT) Philip J. Cameronsmith wrote:
> Subject: Re: [CF-metadata] standard names for chemistry - MCM
>
> "[...] In practice, gas phase chemicals are typically recorded using number of
> moles, while aerosols are usually recorded using mass. Hence, the G for
> gases, A for aerosols, and X for the combined set of G and A. But because
> of the discussion above, it would be possible to force the gases and
> aerosols to always have the same units for CF (as long as the Molar Mass
> is recorded or prescribed for each specie)."
>
> Hi Philip,
>
> but this is why we define the physical quantity in the standard name, don't we?
>
> Example: mass_fraction_of_ and mole_fraction_of_
>
> In my view the "X", "A" and "G" is purely cosmetic to guide the choice of subset of matrix elements. Certain "names" (or properties) just don't make sense for gaseous compounds but are relevant for aerosols (and vice versa). [perhaps Christiane can jump in if I missed something here] There is no need to force anyone to adopt a specific unit. But your discussion about the "effective" molar mass reinforces the point that the molar mass that is assumed/used in the data must be documented so that people can easily convert from one into the other quantity. BTW: the distinction between mass and molar quantities also holds for all "tendency" terms - one can equally well "_due_to_deposition" as a mass quantity (useful for global budgets) or a molar quantity (useful for other things).
>
> "[...] Another option is for CF to allow all possible units for each specie:
> moles_of_X
> mass_of_X
> carbons_of_X
> etc..."
>
> As Jonathan said, this is exactly the reason for the "_expressed_as_" tag. BTW: Do we really need the "expressed" in this? "_as_" should also do the job, no? Some of the standard names have become rather long already...
>
> Best regards,
>
> Martin
>
> < Dr. Martin G. Schultz, ICG-2, 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 >
>
>
>
>
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------------------------------------------------------------------------
Dr Philip Cameron-Smith Atmospheric, Earth, and Energy Division
pjc at llnl.gov Lawrence Livermore National Laboratory
+1 925 4236634 7000 East Avenue, Livermore, CA94550, USA
------------------------------------------------------------------------
Received on Thu Oct 23 2008 - 14:09:55 BST