SIPCO2: A simple, inexpensive surface water pCO₂ sensor

Abstract

Abstract Efforts to estimate air‐water carbon dioxide (CO 2 ) exchange on regional or global scales are constrained by a lack of direct, continuous surface water CO 2 observations. Sensor technology for the in situ measurement of the partial pressure of carbon dioxide (pCO 2 ) has progressed, but still poses limitations including expense and biofouling concerns. We describe a simple, inexpensive, in situ pCO 2 method (SIPCO2) in which a non‐dispersive infrared (NDIR) detector is paired with an air pump in an enclosed housing to produce air‐sea equilibration. We first evaluated this approach in a laboratory setting, then in an estuarine‐coastal ocean laboratory for several months to continuously monitor aquatic pCO 2 . An accepted, accurate NDIR‐based CO 2 measurement technique was employed alongside SIPCO2 to provide an assessment of sensor performance. SIPCO2 allows for low‐cost, relatively accurate measurements of pCO 2 (mean difference of −5 ± 5 μatm from validation system after laboratory calibration) without reagents or membranes, and can be assembled and operated with a minimal amount of technical skill. While not suitable for some exacting applications, this SIPCO2 approach could rapidly and effectively increase the number of quality CO 2 observations in a range of aquatic environments. We also provide detailed instructions for the assembly of SIPCO2 from commercially available components.