Figure 4

Comparison of output from four Method I and three Method II models. Data are from [52] for the Tsofar 221 well (pH = 6.81, I = 0.041, T = 38°C). Labels on the horizontal axis indicate the choices of input data for each of the seven calculations; different pairs of polysulfide species were used in the case of Method I. ΣS⁰ values measured in different ways were used for Method II (the same ΣS^-II was used in all Method II models). In the upper graph, thermodynamic data used in the computations were taken from [39]–[41] for S₈(aq). In the lower graph, pK_na1 for all H₂S_n⁰ species was set to 3.0 and pK_na2 for all HS_n⁻ species was set to 6.3. Numerical values on which this figure is based are given in Table S-3.