Hi Alison,
One slight misunderstanding. 'per mil' means parts per thousand not parts per million so the units should be written as '1e-3' rather than '1e-6'.
Cheers, Roy.
I have now retired but will continue to be active through an Emeritus Fellowship using this e-mail address.
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Alison Pamment - UKRI STFC <alison.pamment at stfc.ac.uk>
Sent: 11 February 2019 12:49
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] New standard name for 14CO2
Dear Katherine, All,
Katherine and I had briefly discussed this name before it was proposed to the mailing list - the suggestion of using mole_fraction was originally mine. Evidently I had misunderstood the quantity in question, and it's clear from the discussion so far that it wouldn't be appropriate to use mole_fraction in this case. Thank you to Roy and Jonathan for clarifying this (and my apologies to Katherine for misleading advice - I've not come across this quantity before).
It does seem that we will need to introduce some new terminology into standard names. Of Roy's two suggestions I prefer enrichment_of_14C_in_carbon_dioxide_in_air. From Roy's explanation, it looks like the quantity is in effect a ratio of ratios. While I appreciate that this may be referred to as a 'delta' in the chemistry community, 'delta' is often used as a mathematical symbol for calculating a difference or change, so I feel that it's best avoided in the standard name.
Regarding the units of 'per mil', the canonical unit in the standard name table would be written as '1e-6'.
Whichever terminology we choose, certainly we do need a clear definition - in particular if the quantity is being calculated with reference to a particular standard we should include that in the information. Katherine, please could you give us some more details about exactly how this quantity is being measured/calculated in your data?
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> On Behalf Of Jonathan Gregory
Sent: 11 February 2019 04:57
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] New standard name for 14CO2
Dear all
I agree with Roy that delta-14C is not a mole fraction, but a way of expressing the deviation of an isotopic ratio in a sample from a standard isotopic ratio.
The definition Roy gives for delta-13C is shown in several websites. I think we need the precise definition of the quantity being proposed, because there appear to be variou quantities with big and small delta and D, and maybe they are all different, and would need distinct standard names. I think Roy is right that we have not given standard names to such quantities before.
Best wishes
Jonathan
----- Forwarded message from "Lowry, Roy K." <rkl at bodc.ac.uk> -----
> Date: Fri, 8 Feb 2019 12:55:31 +0000
> From: "Lowry, Roy K." <rkl at bodc.ac.uk>
> To: Katherine Pugsley <katherine.pugsley at bristol.ac.uk>,
> "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> Subject: Re: [CF-metadata] New standard name for 14CO2
>
> I think that delta-14CO2 is not the same thing as the mole fraction. Rather, it is an expression of isotopic enrichment/depletion with respect to a standard. Whilst I have no experience of atmospheric 14C, I have come across delta notation a lot with other isotopes in geology and oceanography such as 13C and 18O. There, delta is an expression of the ratio of the target isotope to another isotope in the sample relative to some standard - ((sample 13C/12C ratio / standard 13C/12C ratio) - 1) * 1000 to give a result scaled to per mil. I presume that delta-14C is no different.
>
> I am unaware (i.e. I couldn't find) a precedent for delta values in CF Standard Names. The issue of describing these things has been addressed at length in the BODC parameter descriptions with almost 400 measurement descriptions. A typical example is:
>
> Enrichment with respect to Vienna Pee Dee Belemnite (VPDB) of
> carbon-13 in carbonate in the sediment
>
> This particular example includes information on the specific standard used. Many do not because the information is often unavailable for older data.
>
> A straw man alternative to Kate's proposal could be
>
> enrichment_of_14C_in_carbon_dioxide_in_air
>
> If information on the standard is available then that could be added as an 'enrichment_with_respect_to_whatever' clause or the information could be confined to the long name. The better solution depends upon the use case (e.g. does it require inclusion of data where standard is unknown).
>
> Another approach could be to adopt community vocabulary such as:
>
> delta14C_in_carbon_dioxide_in_air
>
> Others may have alternative suggestions.
>
> I went for 'enrichment of x' in the BODC dictionary because it provides a better fit to a normalised semantic model for mapping purposes. One only has to include one 'enrichment' rather than a long list of 'deltas' in the semantic element.
>
> Cheers, Roy.
>
>
> I have now retired but will continue to be active through an Emeritus Fellowship using this e-mail address.
>
> ________________________________
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of
> Katherine Pugsley <katherine.pugsley at bristol.ac.uk>
> Sent: 08 February 2019 10:46
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] New standard name for 14CO2
>
>
> Dear All,
>
> I'd like to request an addition to the standard name list for atmospheric 14CO2 measurements. Here are the details of the proposed standard name.
>
> Proposal for a new standard variable name
>
> Name: mole_fraction_of_14C_dioxide_in_air
>
> Canonical Units: 1
>
> Description: Atmospheric 14CO2 measurements are reported in ?14C notation with units of per mil, the deviation from the absolute radiocarbon reference standard. ?14C is used to calculate fossil fuel CO2 content. The long name will contain information that the variable is ?14C.
>
>
>
> Thanks,
>
> Katherine
>
>
>
>
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