PASCO PS-2108 Dissolved Oxygen Sensor User Manual
Page 17
Model No. PS-2108
Dissolved Oxygen Sensor
13
®
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
3
). For values not found in
the table, use the nomogram found on page 28 in Hitchman, 1978.
4
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