Advancing CO₂ emission data quality in cement production through integrated material-, flue gas-, and 3D inventory-based monitoring

Accurate CO₂ emission data are essential for monitoring, reporting, and verification (MRV) in energy-intensive sectors such as cement production. In China's carbon market, emission regulation in the cement sector still relies primarily on material balance-based accounting with low temporal resolution, which constrains real-time supervision and data quality assessment. To improve data timeliness and reliability, online monitoring approaches are increasingly applied. However, individual methods exhibit distinct systematic uncertainties and operational limitations. This study proposes an integrated online monitoring framework that combines three complementary approaches for cement production: second-level material-based monitoring, second-level flue gas-based monitoring, and daily 3D inventory-based monitoring. Using operational data from a 5,000 t/d clinker production line in southern China, the performance, limitations, and applicability of each method for carbon market MRV were assessed. Results show that material-based monitoring is sensitive to material metering points. Flue gas-based monitoring directly measures CO₂ emissions but is strongly affected by stack flow-field heterogeneity and production load variations, underscoring the importance of appropriate flow measurement configuration. Although the 3D inventory-based method has a lower temporal resolution, it provides an independent and stable reference for cross-validation of high-frequency emission estimates. Further analysis indicates that material-based and flue gas-based emissions do not scale proportionally when production load adjusts, reflecting flow-field changes. By integrating high-frequency data reconstruction with SAITS and cross-validation against daily 3D inventory estimates, the proposed framework enhances consistency and reliability across monitoring methods. The findings demonstrate that the combined use of multiple online monitoring approaches can effectively mitigate individual method limitations and support high-integrity MRV in China's cement sector.