Compute total hydrogen ion activity coefficient. The activity coefficient (fH) is used to convert from H+ concentration on SWS scale to H+ activity (ah), as used for NBS scale; likewise fH is used to make the conversion in the opposite direction, from the NBS scale to the SWS scale. Here, fH is taken from Takahashi et al (1982, GEOSECS Pacific Expedition, Chap 3, p. 80) who say: fH is the total activity coeff., which includes contributions from HSO4- and HF [as well as H+].
Takahashi et al. (1982) computed a relationship for fH based on the experimental data from Culberson & Pytkowicz (1973), who determined it experimentally as a function of temperature and salinity. The approach is old and full of uncertainty. Newer approaches are more complicated (Pitzer equations) and big uncertainties remain (Marion et al., 2011; Pilson, 2013).
fH(S=35, T=25)
Total activity coefficient for H+
Salinity on the practical salinity scale, default is 35
Temperature in degrees Celsius, default is 25oC
James Orr james.orr@lsce.ipsl.fr
This total activity coefficient appears in the following basic chemistry equation: \( ah = fH * hsws\), where \(ah\) is the activity of hydrogen ion, \(fH\) is the total activity coefficient, and \(hsws = [H+] + [HSO4-] + [HF]\). In other words, \(hsws\) is the total hydrogen ion conccentration on the seawater scale.
The two pH scales of concern are defined as \(pHNBS = -log10(ah)\) and \(pHSWS = -log10(hsws)\).
Culberson, C.H., & Pytkowicz, R.M. (1973). Ionization of water in seawater. Marine Chemistry, 1(4), 309-316.
Marion G.M., Millero F.J., Camoes M.F., Spitzer P., Feistel R., Chen C.T.A. 2011. pH of seawater. Marine Chemistry 126 89-96.
Pilson M.E.Q. (2013) An introduction to the chemistry of the sea, 2 edn. Cambridge, UK: Cambridge University Press.
Takahashi T., Williams R.T., and Ros D.L. (1982) Carbonate chemistry. GEOSECS Pacific Expedition, Volume 3, Hydrographic Data 1973-1974, 77-83.
pHnbs2sws and pHsws2nbs
## Compute fH
f = fH(T=25, S=35)
print(f)
## Check value: The result is 0.7134043
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