Evaluating the impact of water vapor for aerosol and carbon dioxide detection lidar CO₂ measurement onboard the atmospheric environment monitoring satellite

Abstract

Global warming, driven by greenhouse gas emissions from human activities, poses significant environmental challenges. Accurate greenhouse gas measurement data are crucial for effective emission reduction policies and international cooperation. The spaceborne integrated path differential absorption lidar offers high precision for monitoring global atmospheric carbon dioxide (CO2) concentrations on both days and nights. However, its accuracy can be compromised by water vapor interference. We evaluated the impact of water vapor on CO2 detection, focusing on measurements from an aerosol and carbon dioxide detection lidar onboard the atmospheric environment monitoring satellite. The bias due to water vapor absorption was negligible. However, water vapor broadened the absorption spectrum, causing molecular interference, which could introduce considerable CO2 column concentrations (XCO2) bias. In areas with high water vapor, the bias could exceed 1 ppm. Globally, the annual average bias of XCO2 due to water vapor broadening effects was 0.42 ppm. The analysis highlights the importance to account for water vapor spectrum broadening effects, not only in spaceborne lidar measurements such as ACDL but also in other atmospheric measurement techniques to improve CO2 measurement accuracy and enhance our understanding of global climate change and the carbon cycles.