1：Experimental Design and Method Selection:

The study involved designing a Raman lidar system using the elastic scattering and Raman lidar equations to retrieve CO2 mixing ratios. The methodology included indoor cell measurements for accuracy validation and field tests at an artificial CO2 leakage site.

2：Sample Selection and Data Sources:

Indoor measurements used a CO2 gas cell with VMR ranging from 10% to 100%. Field measurements were conducted at the Eumseong Environmental Impact Evaluation Test Facility in Korea, with CO2 injected into the ground. Data from in situ instruments (VAISALA GMP343) were used for comparison.

3：0%. Field measurements were conducted at the Eumseong Environmental Impact Evaluation Test Facility in Korea, with CO2 injected into the ground. Data from in situ instruments (VAISALA GMP343) were used for comparison. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Components included a Nd:YAG laser (355 nm, 80 mJ, 20 Hz), Schmidt-Cassegrain telescope (

4：24 cm diameter), optical filters (notch filter at 355 nm, CO2 filter at 7 nm, N2 filter at 7 nm, 355 nm filter), photomultiplier tubes (R9880U-210), beam expander (5X), CO2 gas vessel, mass flow controller, vacuum pump, and in situ CO2 probe. Experimental Procedures and Operational Workflow:

For indoor tests, CO2 was injected into a cell, and Raman signals were measured. For field tests, the lidar emitted laser pulses horizontally, collected backscatter signals from CO2 and N2 Raman scattering, and processed data using normalization and regression techniques. Measurements were done at night to avoid sunlight interference.

5：Data Analysis Methods:

Data were analyzed using linear regression to correlate normalized ratios with CO2 VMR, calculating correlation coefficients, mean absolute error, root mean square error, and percentage differences. Error propagation was used to estimate total errors.