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<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si62.svg" display="inlin

We present an experimental technique for determining the pH and the total carbon concentration when CO 2 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 tool for the analysis of the spatial distribution of captured carbon in the DDC flow. • Experimental techniques for determining spatiotemporal pH and carbon concentration. • Utilization of three pH indicators, measuring a dynamic pH range from 4.0 to 9.5. • Applying pseudo equilibrium theory to derive the total dissolved carbon from pH.