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[CF-metadata] new standard name request for pH

From: alison.pamment at stfc.ac.uk <alison.pamment>
Date: Thu, 5 Nov 2009 14:47:12 -0000

Dear John,

Apologies for the delay in responding to this thread, which has been
waiting for attention for some time. I have reviewed the whole thread
and clearly your proposal led to some very detailed discussion. As
there have been no further comments I think the wording of the name

sea_water_pH_reported_on_total_scale

is agreed. I note Jonathan's comment that the pH itself is
dimensionless because it is calculated as a logarithm, therefore it
seems that the canonical units should be '1'. As Jonathan pointed out,
if pH is calculated from a quantity having units of moles kg-1 then that
fact should be included in the definition.

However, I note also the discussion regarding the activity of hydrate
ions as opposed to their concentration and your statement in
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2009/002847.html that
> We will change the proposed definitions to replace 'concentration'
with 'activity'.

Based on the wording you have already provided I think that would lead
us to the following definition:
" 'sea_water_pH_reported_on_total_scale' is the measure of acidity of
sea water, defined as the negative logarithm of the activity of
dissolved hydrogen ions plus bisulfate ions in a sea water medium; it
can be measured or calculated; when measured the scale is defined
according to a series of buffers prepared in artificial seawater
containing bisulfate. The quantity may be written as pH(total) = -
log([H+](free) + [HSO4-])."

My (admittedly not very deep) understanding is that activity can be
regarded as an 'effective concentration' which takes account of the
interactions between molecules in non-ideal solutions and gas mixtures.
Presumably then the equation in the last sentence should be understood
as referring to these effective concentrations? Also, chemical activity
appears to be a dimensionless number by definition, so do we actually
need to include any text about moles kg-1 in the standard name
definition? The name itself is fine, but I'm still confused about the
units and definition, and we need to be clear about those before the
name can be added to the table.

Best wishes,
Alison

>
> I believe this request has been pending for a long time now, with no
> comments since May 26. Can we finalize it? (Please?)
>
> sea_water_pH_reported_on_total_scale:
> The measure of acidity of sea water, defined as the negative logarithm
> of the concentration of dissolved hydrogen
> ions plus bisulfate ions in a seawater medium; it can be measured or
> calculated; when measured the scale is defined according to a series
> of buffers prepared in artificial seawater containing bisulfate.
> pH(total) = - log([H+](free) + [HSO4-]). [canonical units = moles/kg
].
>
> John
>
>
> On May 26, 2009, at 11:38 PM, Jonathan Gregory wrote:
>
> > Dear John
> >
> > Thanks. I'm still happy with
> >> sea_water_pH_reported_on_total_scale
> > which is actually a phrase I found on Google.
> >
> > Best wishes
> >
> > Jonathan
>
>
> John
>
> --------------
> John Graybeal <mailto:graybeal at mbari.org> -- 831-775-1956
> Monterey Bay Aquarium Research Institute
> Marine Metadata Interoperability Project: http://marinemetadata.org
>

------
Alison Pamment Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre Fax: +44 1235 446314
Rutherford Appleton Laboratory Email: alison.pamment at stfc.ac.uk
Chilton, Didcot, OX11 0QX, U.K.
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