YSI ADV6600 - Manual (Page 195)

ADV6600
Y S I Environmental
Page 185
Appendix F. Percent Air Saturation
The term “Percent Air Saturation” (abbreviated in many applications to “Percent Saturation”) is a
common parameter for expressing the state of the oxygenation of environmental water and is widely
used by YSI and other manufacturers during the calibration of oxygen sensors. However, because
the parameter can be expressed by two different conventions, there can be confusion around the use
of the term. This section is designed to minimize that confusion by defining each of these
conventions and providing instructions for configuration of the ADV6600 sonde so that you will
have a choice as to which of the conventions is used.
Note: No matter which of the conventions is employed (in YSI or competitive instrumentation), the
values of dissolved oxygen in mg/L will be identical and unaffected by the choice of DO %
convention.
F-1. “DOsat %” Convention
The first convention has been used for many years in YSI handheld and laboratory instruments and
in 6-series sondes. The "%saturation" value at the time of calibration in air reflects the value of the
barometer or altitude that was input in the calibration protocol. If the parameter “DOsat %” is active
in your 6-series Report menu, then this convention is being used. Effectively, this convention
provides a value of water oxygenation that can be carried out by air exposure, with the value
referenced to having the air at exactly 1 atmosphere (760 mm Hg or 101.3 kPa). A “DOsat %”
value of 89 means that the water contains 89 % of the oxygen that could be dissolved if the water
was introduced with air that had a total pressure of 1 atm.
For example, when performing an air calibration in the mountains at a typical barometric pressure of
630 mmHg, the YSI “DOsat %" value at calibration would read 82.9 % (630/760 * 100). Assume
the sensor did not drift electrochemically and the sonde was taken to a location where the
atmospheric pressure was exactly 760 mm Hg (e.g., sea level). The “DOsat %” reading in air (or
air-saturated water) would change to 100 % (760/760 *100) because there is more total oxygen in
the air at the lower elevation.
Note that the percent oxygen in the air is effectively independent of the barometer or altitude.
Assume the water at both sites has a temperature of 20º C, where water exposed to water-saturated
air at exactly 760 mm Hg is 9.09 mg/L. The mg/L value would be 7.54 mg/L (0.892 * 9.09) in the
mountains and 9.09 mg/L (1.00 * 9.09) at sea level. Thus, to calculate mg/L values at any site after
calibration using this convention, the observed “DOsat %” values are simply multiplied by the
Standard Methods or ISO table values that correspond to 100 % at various temperatures and salinity.