Solubility of oxygen in the major sea salts as a function of concentration and temperature

The solubility of oxygen has been measured in NaCl, Na2SO4, MgCl2 and MgSO4 solutions from 5 to 45 °C from 0.1 to saturation. The solubilities, [O2], have been fitted to a Setschenow [J. Phys. Chem. 4 (1899) 117] type equation ln{[O2]0/[O2]}=lnγ=Am+Bm2where the superscript zero is the solubility of oxygen in water, m is the molality and γ is the activity coefficient of O2. The adjustable parameters A and B are determined by least squares to equations of the form (T/K)A=a00+a01/T+a02ln T and B=b00+b01/T+b02ln T. The standard errors of all the fits of [O2] are less than ±2.0 μmol (kg H2O)−1 for all the salts. The limiting values of kS=A for the solutions have been determined from the fits. The ionic values of kS for SO42− are not additive due to the strong interactions between Mg2+ and SO42−. The results have been interpreted using the Pitzer equations where λO2i is a parameter that accounts for the interaction of O2 with cations (c) and anions (a) and ζO2ca accounts for interactions for O2 with the cation and anion (c–a). The coefficients (λO2i) determined for Na+, Cl− and SO42− are in reasonable agreement with the tabulations of Clegg and Brimblecombe [J. Phys. Chem. 93 (1990) 7237]. The values of λO2c for the interactions of Na+, Mg2+, SO42− and ζO2ca for the interactions of NaCl, Na2SO4, MgCl2 and MgSO4 with O2 from 5 to 45 °C (T/K) have been fitted to equations of the form (λO2Cl=0) λO2Na=−24.2231+1169.14/T+3.58915lnT λO2Mg=−40.3039+1912.70/T+5.99055lnT λO2SO4=44.8440−1956.75/T−6.69935lnT ζO2NaCl=5.7292−260.89/T−0.85431lnT ζO2MgCl2=19.715−888.35/T−2.93893lnT ζO2Na2SO4=18.8007−862.37/T−2.79870lnT ζO2MgSO4=25.4448−1186.25/T−3.77264lnTThese parameters represent the oxygen solubilities to ±2.0 μmol (kg H2O)−1 over the entire range of temperature and concentration. The resulting coefficients for the major sea salts can be used to estimate the solubility of oxygen in all natural waters over a wide range of temperature and ionic strength.