User's Manual

Model No. PS-2108 Dissolved Oxygen Sensor

equilibrium.

A famous, naturally occurring case of supersaturation and subsequent gas release (in this

case it was dissolved carbon dioxide gas) was the Lake Nyos tragedy, which took place in

Cameroon (1986).

4. Salinity.

• Salt and other solids dissolved in water will affect the total amount of gas that a liquid

solvent can dissolve. Given otherwise identical conditions, fresh water can hold more

dissolved oxygen than salt water. When measuring dissolved oxygen in salt water (in

excess of 1000 mg/L dissolved salts), calibrate the probe in a sample of the salt water in

which the DO measurement is desired. For situations in which the salt content is not

constant (such as estuarine environments) one must calibrate the probe using fresh water.

For each DO reading, one must also make an accurate determination of dissolved salt

content in order to account for the change in oxygen solubility in waters of varying salinity.

• To obtain theoretical maximum DO in saline waters, consult the following table for the

theoretical maximum dissolved oxygen at saturation-the low calibration value will remain

at 0 mg/L DO (table from Ambient Water Quality Criteria, 1997

). For values not found in

the table, use the nomogram found on page 28 in Hitchman, 1978.

Solubility of oxygen in water (fresh and saline) exposed to water-saturated air at sea level

760 mm Hg (101.3 kPa)

Chlorinity (freshwater)

Temp.

(°C)

0 g/L Cl- 5.0 g/L Cl- 10.0 g/L Cl- 15.0 g/L Cl- 20.0 g/L Cl- 25.0 g/L Cl-

0.0 14.621 13.728 12.888 12.097 11.355 10.657

1.0 14.216 13.356 12.545 11.783 11.066 10.392

2.0 13.829 13.000 12.218 11.483 10.790 10.139

3.0 13.460 12.660 11.906 11.195 10.526 9.897

4.0 13.107 12.335 11.607 10.920 10.273 9.664

5.0 12.770 12.024 11.320 10.656 10.031 9.441

6.0 12.447 11.727 11.046 10.404 9.799 9.228

7.0 12.139 11.442 11.783 10.162 9.576 9.023

8.0 11.843 11.169 10.531 9.930 9.362 8.826

9.0 11.559 10.907 10.290 9.707 9.156 8.636

10.0 11.288 10.656 10.058 9.493 8.959 8.454

11.0 11.027 10.415 9.835 9.287 8.769 8.279

12.0 10.777 10.183 9.621 9.089 8.586 8.111

13.0 10.537 9.961 9.416 8.899 8.411 7.949

14.0 10.306 9.747 9.218 8.716 8.242 7.792