Mapping dissolved carbon in space and time: An experimental technique for the measurement of pH and total carbon concentration in density driven convection of CO$_2$ dissolved in water

TL;DR

This paper introduces an innovative experimental technique using multiple pH indicators and image analysis to map the spatial distribution of pH and total carbon concentration in water affected by CO2 diffusion and convection.

Contribution

The method allows continuous spatial mapping of pH and carbon levels, surpassing traditional single-indicator techniques, and is validated in density-driven convection experiments.

Findings

Successfully calibrated against benchmark solutions.

Demonstrated in density-driven convection of carbon-enriched water.

Provides detailed spatial distribution of dissolved carbon.

Abstract

We present an experimental technique for determining the pH and the total carbon concentration when \ch{CO2} diffuses and flows in water. The technique employs three different pH indicators, which, when combined with an image analysis technique, provides a dynamic range in pH from 4.0 to 9.5. In contrast to usual techniques in which a single pH indicator is used, the methodology presented allows not only to produce a binary classification (pH larger or smaller than a given threshold) but to access a much more complete continuous spatial distribution of pH and concentration levels in the system. We calibrate the method against benchmark solutions and further demonstrate its potential by measuring the pH and total carbon concentration in a density driven convection (DDC) of carbon-enriched water. The motivation for testing the method in this particular experiment comes from the fact that DDC plays a pivotal role in the efficiency of engineered carbon storage processes. The application of the technique presented here provided a direct window for the analysis of the spatial distribution of captured carbon in the DDC flow.