Why are there so many ‘pH scales’ for measuring seawater ‘pH’? What do they mean?

pH is an important property of aqueous solutions because it affects a wide variety of chemical and biochemical properties through its role in acid-base reactions. This importance and the ease of pH measurement are the reasons why pH is perhaps the most measured chemical parameter in many environmental systems. A primary rationale for pH measurements is to enable calculation of the speciation in acid-base systems such as the CO2 system in seawater. However, the notional definition of pH, pH = –lg a(H+), does not lend itself to straightforward application to seawater systems, and, as a result, a number of alternate seawater ‘pH’ scales have been developed over the years. These various ‘pH’ scales have different meanings, and incorporate differing assumptions and calibration approaches, yet each of the various measurements is often simply referred to as ‘pH’, inviting confusion.

In this webinar how these various ‘pH’ scales arose; detail on how they differ; and the perceived advantages and disadvantages of the various approaches are outlined. Finally, how to choose an approach that is suited to your scientific goals, and how best to implement it and use it is discussed.

This webinar is hosted by the US Interagency Working Group on Ocean Acidification, a collaborative working group of 13 federal agencies that aims to coordinate and foster Federal research and monitoring on ocean acidification.