Lime carbonation direct air capture (DAC) systems remove atmospheric carbon dioxide (CO2) by carbonating calcium hydroxide (Ca(OH)2) to produce calcium carbonate (CaCO3), which can release CO2 for durable storage. Accurate and precise measurement of generated CaCO3 is essential in quantifying CO2 removed from the atmosphere, and for optimizing the carbonation process. Methods for measurement of carbonate content are well established, but have yet to be applied to materials produced by this system (i.e., almost solely Ca(OH)2 and CaCO3). Five carbonate content analysis techniques (loss on ignition, LOI; thermogravimetric analysis, TGA; combustion analysis of carbon via infrared absorption, CAC-IR; volumetric calcimetry; and quantitative Fourier transform infrared spectroscopy, FTIR) were investigated for their measurement accuracy and precision over a range of carbonate contents. Sample throughput and levelized cost of analysis were considered in addition to accuracy and precision. LOI and CAC-IR proved favorable against equal consideration of the four factors. Weighting for accuracy and precision, LOI was favorable. Standard operating procedures, including established accuracy and precision levels, for viable carbonate content quantification techniques should be developed, tested, and presented to assure carbon credit buyers, the scientific community, and the public on the validity of carbon credits generated by lime carbonation DAC.

Soil porewater chemistry underpins the quantification of carbon dioxide removal (CDR) in enhanced rock weathering (ERW), where alkalinity and dissolved ion measurements are used within monitoring, reporting and verification (MRV) frameworks. The reliability of these measurements depends on the extraction method, with many in-field techniques constrained by soil moisture availability. This dependence can limit data continuity, reduce comparability across sites and seasons and introduce uncertainty into CDR-relevant interpretations. Here, we present and evaluate a new soil porewater extraction method, SATuration–Centrifugation (SAT-C), designed to obtain porewater from a defined soil volume independent of moisture conditions. The method combines saturation of intact soil cores using deionized water with centrifugation to recover porewater for chemical analysis. We compare SAT-C with conventional sampling using soils collected from grassland field sites, including sites amended with crushed basalt as part of ERW field trials. Across sites, SAT-C porewater chemistry shows strong agreement with rhizon samples for major ions, and bicarbonate concentrations inferred from charge balance are consistent with measured alkalinity. These initial results show that SAT-C provides a robust and reproducible approach for soil porewater extraction, with the potential to improve sampling reliability across variable conditions and thereby support more reliable carbon accounting in ERW.