Observing atmospheric isoprene over Amazon from hyperspectral infrared sounders onboard China’s FengYun-3 satellites

Isoprene is the most abundant non-methane volatile organic compound (VOC) emitted by terrestrial vegetation. Owing to its high reactivity, isoprene is rapidly removed through oxidation by the hydroxyl radical (OH), thereby playing a key role in modulating atmospheric composition, including secondary organic aerosol formation, tropospheric ozone production, and the lifetime of methane. However, due to sparse in-situ measurements in remote tropical regions and the limited early-afternoon overpass (~13:30 local time) of the Cross-track Infrared Sounder (CrIS), the diurnal variability of isoprene emissions is still poorly constrained. Fengyun-3E (FY-3E) is the world’s first civilian meteorological satellite operating in a dawn-dusk orbit and is equipped with the second-generation Hyperspectral Infrared Atmospheric Sounder (HIRAS-II). It enables retrievals of isoprene by capturing isoprene spectral signal and provides unique late-afternoon (~17:30 local time) overpass data, complementing existing early-afternoon measurement capabilities. Using spectral data from FY-3E/HIRAS-II and CrIS, this study employed a full-physics retrieval algorithm based on the optimal estimation method to derive isoprene column abundances over Amazon from 2023 to 2025. The resulting isoprene retrievals exhibit consistent spatiotemporal patterns between HIRAS-II and CrIS observations, and are further validated against previous CrIS retrievals, in situ measurements, and GEOS-Chem model. Sensitivity tests using model simulations were conducted to evaluate the roles of emission and chemical processes in controlling isoprene variability. Our results provide the first direct satellite-based characterization of daytime isoprene variations, offering new insights into the biosphere-atmosphere interactions and their implications for atmospheric chemistry-climate coupling in the Amazon region.