LaMotte DO 6 Dissolved Oxygen Meter - Manual (Page 50)

14.1.2 Measurement Units
One measure of DO in water is parts per million (ppm) which is the number of
oxygen molecules (O
2
) per million total molecules in a sample. Calculating
the % Saturation is another way to analyze DO levels. % Saturation is the
measured DO level divided by the greatest amount of oxygen that the water
could hold under various temperature and atmospheric pressure conditions
multiplied by 100.
14.1.3 What Is Being Measured?
DO probes respond to the partial pressure of oxygen in liquid or gas being
measured – they measure the “pressure” of oxygen rather than concentration.
All of the oxygen entering the probe is consumed at the cathode where it is
Solubility of oxygen in water contact with water saturated air at
standard atmospheric pressure
Solubility
mg/L
16
14
12
10
8
6
4
2
0
0 10 20 30 40 50 60
Temperature °C
49