electrolytic hygrometer

https://doi.org/10.1351/goldbook.E01972
@[email protected] using a hygroscopic substance (for example, diphosphorus pentaoxide, P2O5) which is transformed into an electrolyte (phosphoric acid, H3PO4) in contact with the moisture in the gas. The electrolyte (phosphoric acid) is electrolysed continuously and the electrolysis current is measured. At a constant flow of the gas to be analysed, the electrolysis current is a linear function of the water concentration.
Source:
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2195 [Terms] [Paper]