pCO2aq temperature dependence in popular Phreeqc-compatible databases

[Steve]

Hi All

Just to let you know that I recently discovered some significant discrepancies in the pCO2aq temperature dependence (ppmv/K or uatm/K)) of 4 popular databases uses with Phreeqc3 and only one is close to the commonly accepted value. I arbitrarily used a 10 C range from 12.6 C  to 22.6 C i.e. 5 C either side of 17.6 C (which is I think believed to be the current mean temperature of the oceans).
Here they are:

phreeqc.dat   21.2
thermoddem  22.4
llnl                15.2
wateq4f         21.3

It is my understanding that the best modern literature estimate for this value (used widely in climate science) is close to 17 ppmv/K so if you are doing sensitive temperature-dependent involving work with CO2, HCO3- and CO3-2 equilibria it would clearly be best to use the llnl (Lawrence Livermore) database by preference, understanding that the best modern value is still about 12% higher than the llnl value.

[Charlie]

Hi Steve,
Thanks for sharing your findings! I'm sure that this information will be of use to many.  We hope that the forum is useful for your work.
Please keep contributing! (perhaps you could describe your work and how you use PHREEQC?)
Cheers, Charlie