Hi Christiane,
Please check out the previous postings. There are in fact 3 pH scales covering pH based on a concentration per kg: one based on H+, a second on H+ and bisulphate and a third on H+, bisulphate and HF. We did consider having 4 Standard names but I was arguing for just 2 based on H+ alone to try and match the level of specialism covered with other areas.
The negative log transform between the appropriate concentration term and 'pH' has always been taken as read by all involved in the discussion, but maybe we should be more explicit when it comes to term definitions.
Oceanographers are moving towards expressing chemical data in the dimension moles/kg rather than moles/litre. We need a standardised convention to distinguish these as they have different canonical units and therefore need different Standard Names. I think the approach Jonathan is taking is the most sensible way to do this without large scale deprecation of existing names. We must always remember to include definitions and to read them: they are the key to eliminating confusion.
Cheers, Roy.
________________________________________
From: cf-metadata-bounces at cgd.ucar.edu [cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Christiane Textor [christiane.textor at lsce.ipsl.fr]
Sent: 30 April 2009 17:13
To: Lowry, Roy K; Jonathan Gregory
Cc: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] new standard name request for pH
Dear all,
I am not an expert ocean acidification at all, but there are some
general questions I have concerning these names for the pH of sea water:
1) large scale medium
Why not use sea_water (or ocean_) as a prefix as we have agreed on?
2) definded_by
For the atmospheric chemistry names we have used expressed_as, why not
use this here as well?
3) definition of pH (-log(H+))
As far as I know the pH is defined as the negative logarithm of the
concentration of H+ (or whatever else), this is missing in the suggested
names. I would suggest to use expressed_as instead of defined_by to
circumvent this problem.
4) definition of pH (N.B.S or free)
I have checked the different definitions of the pH in sea water and it
seems to me that the NBS and the free pH do not all refer to the
concentration of H+ alone but consider also other ions, please see
http://en.wikipedia.org/wiki?title=Talk:Ocean_acidification#cite_note-zeebe-0
(rather bad page, but still..)
Am I confused?
5) concentration
For the atmospheric chemistry names we have mass_concentration and
mole_concentration which is mass or mole per volume. This means that
concentration always means per unit volume, and not per unit mass.
If you say now concentration per unit mass, this is confusing.
Best regards,
Christiane
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Received on Thu Apr 30 2009 - 11:49:52 BST
