Global Nighttime Aerosol Optical Depth

This study presents a new algorithm for retrieving nighttime aerosol optical depth (AOD) from thermal infrared radiance measurements acquired by the Atmospheric Infrared Sounder (AIRS). The resulting AOD dataset covers most of the low- and mid-latitude regions. For the first time, aerosol retrieval has been achieved using long-wave radiation within the atmospheric window. This innovation not only offers a fresh approach to nighttime AOD retrieval and reveals diurnal differences in AOD, but also underscores the importance of long-wave radiation in aerosol studies. Because long-wave radiation is available both day and night and is unaffected by bright surface conditions, the method holds significant potential for applications in environmental and climate research.