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-boun...@cgd.ucar.edu [cf-metadata-boun...@cgd.ucar.edu] On Behalf Of Christiane Textor [christiane.tex...@lsce.ipsl.fr] Sent: 30 April 2009 17:13 To: Lowry, Roy K; Jonathan Gregory Cc: cf-metadata@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 _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata -- This message (and any attachments) is for the recipient only. NERC is subject to the Freedom of Information Act 2000 and the contents of this email and any reply you make may be disclosed by NERC unless it is exempt from release under the Act. Any material supplied to NERC may be stored in an electronic records management system. _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata