Direct In Situ Measurement of Alkalinity Export for Real-Time Enhanced Weathering MRV

Accurate quantification of alkalinity export from the near-field zone remains a key bottleneck for monitoring, reporting, and verification (MRV) of carbon dioxide removal (CDR) through Enhanced Weathering (EW). Here we validate the Everest Pulsar, a field-deployable alkalinity sensor that accumulates total alkalinity (TA) using a weak acid ion-exchange resin and transduces resin saturation into a digital, in situ measurement. In a 7-day continuous-flow soil column experiment (10 no-soil, 5 soil units), the sensor quantitatively retained incoming alkalinity, with capture efficiencies of 98.9% (SD=0.3%) without soil and > 97.7% (SD=0.2%) with soil. Combined capture-and-recovery efficiencies were 98.8% (SD=4.1%) and at least 93.9% (SD=1.3%) for no-soil and soil units respectively. Effluent alkalinity remained well below 2% across all loading states, and mass-balance residuals averaged 0.1% (SD=4.3%) without soil and 4.0% (SD=1.3%) with soil. The digital readout closely matched chemically recovered TA with an average deviation of -0.3% (SD=6.0%). These results provide the first quantitative validation of an in situ sensor capable of measuring cumulative alkalinity export and demonstrate a practical path toward accurate, cost-effective, real-time MRV of EW carbon removal.