A new technique to measure CO₂ mixing ratio at industrial stacks plumes based on Raman Lidar remote sensing

Carbon dioxide (CO₂) emissions from industrial point sources are one of the main driving factors contributing to uncertainties in CO₂ emissions from fossil fuels. This study demonstrates, for the first time, the feasibility of a portable Raman Lidar system that is cost-effective and employs simple optics for the monitoring of anthropogenic CO₂ emissions from stack sources. Two outdoor field campaigns were conducted to investigate emissions from waste combustor stacks in South Korea. In Haman, we examined the CO₂ enhancement caused by emissions and estimated the CO₂ instant emission flux over a waste combustor stack, which was located 440 m away from the Lidar. The CO₂ volume mixing ratio peaked at 856.05 ppmv on the night of August 22, 2022, demonstrating effective CO₂ source capture. Higher standard deviations on the night of August 22 were correlated to calm and light wind conditions. Instant emission fluxes were calculated at 265.6 kg/h (night of August 15) and 622.6 kg/h (night of August 22). Interestingly, the CO₂ emission flux over the stack varied significantly with time, which implied the importance of continuous CO₂ emission tracking. In Seoul, CO₂ emission measurements were conducted on April 27, 2022, and a broader CO₂ plume was detected compared to the observations in Haman. Instant emission fluxes were quantified at 771.3 kg/h (22:38) and 623.4 kg/h (22:49) over the stack, which was located 820 m away from the Lidar. Furthermore, the performance of the Raman Lidar was evaluated based on the comparison between Lidar measurements and data collected from in situ CO₂ sensors. The outcomes validated the high accuracy of the Lidar under outdoor conditions (averaged percent difference = 0.06 %). Our study highlights the efficacy of Raman Lidar in tracking high CO₂ emissions, thereby contributing to the quantification of greenhouse gas emissions and supporting global climate action initiatives.