While mineral-based ocean alkalinity enhancement (OAE) has emerged as a promising carbon dioxide removal strategy through the addition of alkaline minerals to water, its effectiveness depends on accurate quantification of the resulting total alkalinity (TA) increase. While it is well-recognized that suspended particles can bias titration-based TA, whether addition of minerals introduces systematic TA artifacts remains poorly quantified. Our laboratory experiments have confirmed that ultrafine limestone particles (<0.2 μm) can introduce a systematic positive bias in titration-based TA measurements. The magnitude of this bias increases with limestone addition but decreases under elevated pCO₂ as greater mineral dissolution reduces the abundance of ultrafine particles. In contrast, the bias becomes negligible when ultrafine particles are excluded from the added minerals. Over the next several months, we will conduct additional incubation experiments to determine how different minerals and key environmental factors, including pCO₂, temperature, and organic matter, influence the contribution of ultrafine particles to TA titration. These results will improve the accuracy of alkalinity measurements and strengthen monitoring, reporting, and verification frameworks for mineral-based OAE.
 

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