The atmospheric concentration of carbon dioxide (CO₂) has continuously increased over the last decades due to rapid population growth and increasing emissions from burning fossil fuels. The absorption of atmospheric CO₂ in the oceans affects the balance of the carbonate system, in which the availability of carbonate ions decreases while the amount of hydrogen ions increases, leading to acidification. The partial pressure of CO₂ (pCO₂) dissolved in seawater is often indirectly determined through a mathematical calculation involving two variables of the carbonate system, commonly pH, total alkalinity (TA), or dissolved inorganic carbon (DIC). This requires the availability of expensive equipment, materials, and reagents necessary for analyzing each variable, and these techniques are usually demanding in terms of human resources. In this study, a new methodology for the direct analysis of pCO₂ in discrete seawater samples was implemented with a small gas balancer and direct measurement with a CO₂ detector (LICOR-850). It was compared to the indirect measurement through DIC and pH as reference methodology. We found a good analytical quality in the proposed methodology, with an accuracy of 106%, a limit of quantification 20 times lower than the average surface seawater value, a linearity of 0.9991, and robustness to variations of typical seawater salinities. Hence, the proposed method is a simple and cheap technique for analyzing pCO₂ in marine-coastal seawater, which can be used in other regions where budgetary constraints limit its long-term monitoring.

Primary Presenter: MARTIN RANGEL-GARCIA, Universidad Nacional Autónoma de México (martin.r.gq31@hotmail.com)

Authors:

Martín Rangel-García, Universidad Nacional Autónoma de México, Posgrado en Ciencias Químicas.  (martin.r.gq31@hotmail.com)

Joan Sanchez-Cabeza, Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, Unidad Académica Mazatlán.  (jasanchez@cmarl.unam.mx)

Ricardo Martínez-Galarza, Universidad Nacional Autónoma de México, Posgrado en Ciencias del Mar y Limnología.  (carbonilo100794@gmail.com)

Marcela Fregoso-López, Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, Unidad Académica Mazatlán.  (mfregoso@ola.icmyl.unam.mx)

Arturo García-Mendoza, Universidad Nacional Autónoma de México, Facultad de Estudios Superiores Cuautitlán, Departamento de Ciencias Químicas.  (arturogm@unam.mx)

Ana Ruiz-Fernández, Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, Unidad Académica Mazatlán.  (caro@ola.icmyl.unam.mx)