The role of pHT measurements in marine CO2-system characterizations |
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| Institution: | 1. Department of Marine Science, University of South Florida, 140 Seventh Avenue South, St. Petersburg, FL 33701 USA;2. Merck and Company, P.O. Box 4, WP36A-101, West Point, PA 19486 USA;3. Pacific Marine Environmental Laboratory, NOAA, 7600 Sand Point Way NE, Seattle, WA, 98115 USA;4. Rosenstiel School of Marine and Atmospheric Science, University of Miami, FL 33149 USA;1. Center for Energy Resources Engineering (CERE), Department of Chemical and Biochemical Engineering, Technical University of Denmark, Building 229, DK-2800 Kgs. Lyngby, Denmark;2. CAPEC-PROCES Research Center, Department of Chemical and Biochemical Engineering, Technical University of Denmark, Building 227, DK-2800 Kgs. Lyngby, Denmark;1. State Key Laboratory of Electronic Thin Films and Integrated Devices, National Engineering Research Center of Electromagnetic Radiation Control Materials, School of Microelectronics and Solid-State Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China;2. Electrical and Computer Engineering Department, Northeastern University, Boston, MA 02115, USA;1. Department of Agrochemistry and Environment, Miguel Hernández University, Ctra. de Beniel, 03312 Orihuela, Alicante, Spain;2. Estación Experimental Agraria, Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra. de Dolores Km. 1, 03290 Elche, Alicante, Spain;3. Food Quality and Safety Group, Department of AgroFood Technology, Miguel Hernández University, Ctra. de Beniel, 03312 Orihuela, Alicante, Spain;1. Université de Toulouse; INSA, UPS, INP; LISBP, 135 Avenue de Rangueil, F-31077 Toulouse, France;2. INRA, UMR792 Ingénierie des Systèmes Biologiques et des Procédés, F-31400 Toulouse, France;3. CNRS, UMR5504, F-31400 Toulouse, France;4. Université de Toulouse; INPT, UPS; Laboratoire de Génie Chimique UMR CNRS 5503; 4, Allée Emile Monso, F-31030 Toulouse, France;5. IDTQ?Grupo Vinculado PLAPIQUI?CONICET-FCEFyN, Universidad Nacional de Córdoba, X5016GCA, Av. Vélez Sarsfield 1611, Córdoba, Argentina |
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| Abstract: | Spectrophotometric pHT measurements can routinely be obtained with an imprecision on the order of ±0.0005 pHT units. This level of imprecision is equivalent to an imprecision in total hydrogen ion concentration of ±0.1% (where pHT=?logH+]T and H+]T?H+]+HSO4?]). At this level of precision, pHT measurements provide an important tool in quality control assessments of other CO2-system parameters (CO2 fugacity, total inorganic carbon, total alkalinity). CO2 fugacities and total alkalinities calculated using measured pHT and total inorganic carbon, for the large data set considered in this work, have relative precisions on the order of 0.15 and 0.1%, respectively. The precision of total inorganic carbon calculated via pHT and salinity-normalized-alkalinity is on the order of 0.02% or better. In this work, using the NOAA 1992 boreal autumn Equatorial Pacific (EqPac) dataset, it is shown that CO2-system variables calculated via pHT can be used to enhance both the precision and accuracy of directly measured parameters. Through the procedures described in this work significant problems were revealed in the initial version of the 1992 NOAA dataset, and the dataset was greatly improved. Additionally, in this work, we revisit CO2-system thermodynamic consistency issues in view of changes in the pHT values assigned to tris seawater buffers and consequential changes in the calibration of sulfonephthalein pHT indicators. As the principal result of a +0.0047 increase in the pK of meta cresol purple, CO2 fugacity calculations and measurements are in very good agreement for the NOAA 1992 boreal autumn EqPac dataset. We note, as well, that due to a reassignment of the titrant acid concentration used in the NOAA 1992 boreal autumn dataset, measured total alkalinities are in good agreement with total alkalinities calculated from total carbon and pHT. |
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