Water vapor retrievals from the ground-based direct-Sun measurements based on the spectral Langley method

Water vapor is one of the most important species in the hydrological cycle, mainly emitted from ocean evaporation. In this study, we deployed the Spectral Measurements for Atmospheric Radiative Transfer-spectroradiometer (SMART-s) and AErosol RObotic NETwork (AERONET) instruments at Suwon, South Korea, during the Airborne and Satellite Investigation of Asian Air Quality (ASIA-AQ) campaign from December 2023 to February 2024. The newly developed SMART-s total precipitable water (TPW) retrieval algorithm utilizes direct-Sun measurements based on the spectral Langley calibration method. The SMART-s retrievals of the TPW showed excellent agreement with the collocated AERONET products (correlation coefficient of 0.99, slope of 1.03, and offset of-0.04). The TPW measurements from globally networked SMART-s or Pandora instruments can provide valuable information for analyzing interactions between trace gases (e.g., H2O, NO2, HCHO, SO2,O3), aerosols, and clouds, thereby contributing to understanding its role in the climate and hydrological systems.