Long-Term IASI Observations of Upper Tropospheric CO in the Asian Summer Monsoon Region: Trends and Eddy Shedding Signatures

Year: 2026

Authors: Boynard A., Viatte C., Pan LL., Honomichl SB., Lazaro AL., Sinnathamby S., Hadji-Lazaro J., Smith WP., Liang Q., D’Amato F., Viciani S., Campos T., Clerbaux C.

Autors Affiliation: Sorbonne Univ, LATMOS IPSL, UVSQ, CNRS, Paris, France; SPASCIA, Ramonville St Agne, France; NSF Natl Ctr Atmospher Res, Atmospher Chem Observat & Modeling Lab, Boulder, CO USA; NASA, Goddard Space Flight Ctr, Greenbelt, MD USA; Ist Nazl Ott CNR INO, Consiglio Nazl Ric, Sesto Fiorentino, Italy; Univ Libre Bruxelles ULB, Spect Quantum Chem & Atmospher Remote Sensing, Brussels, Belgium.

Abstract: The Asian Summer Monsoon (ASM) acts as a key mechanism for the vertical transport of surface pollutants into the upper troposphere (UT), which can have far-reaching impacts on air quality and climate at regional to global scales. We analyze 16 years (2008-2023) of carbon monoxide (CO) observations from the Infrared Atmospheric Sounding Interferometer (IASI) to investigate UT variabilities over the ASM region. Seasonal cycles, long-term trends, and dynamic features such as eddy shedding are examined to assess pollution transport within and beyond the ASM anticyclone. IASI observations are sensitive in the 12-15 km range, showing reasonable agreement with in situ aircraft observations from the 2022 Asian Summer Monsoon Chemical and Climate Impact Project (ACCLIP), with a mean bias of -16.1% +/- 11.4%. A significant decline in CO concentrations is observed over the ASM region over 2008-2023, with trends of -5.4% per decade in total column and -13.3% per decade in the UT, consistent with reduced anthropogenic surface emissions in Asia over this period. CO patterns from 2008 to 2023 reveal persistent enhancements aligned with the Tibetan Plateau and Western Pacific anticyclone modes, confirming for the first time IASI’s ability to capture the ASM dynamical signatures on climatology-relevant time scales. A case study of an eddy shedding event shows long-range transport of ASM-sourced CO across the Pacific toward North America. These results highlight the added-value of IASI observations as a long-term indicator of ASM-driven pollution in the UT and its significance in both regional and intercontinental transports.

Journal/Review: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES

Volume: 131 (11)      Pages from: e2025JD045647-1  to: e2025JD045647-1

More Information: IASI is a joint mission of EUMETSAT and the Centre National d’Etudes Spatiales (CNES, France). The authors acknowledge the Aeris data infrastructure (https://www.aeris-data.fr/) for providing access to the IASI data used in this study, ULB-LATMOS for the development of the retrieval algorithms, and EUMETSAT/AC SAF for CO data production. This work was undertaken in the framework of the EUMETSAT AC SAF project (http://acsaf.org). The French scientists also acknowledge the financial support of CNES via the DYNAMICA research project from the TOSCA (Terre Ocean Surface Continentale Atmosphere) committee. The authors thank the Copernicus Climate Data Store for providing ERA5 data. LLP, SBH, and WPS are supported by the National Science Foundation (NSF) National Center for Atmospheric Research (NCAR), which is a major facility sponsored by the U.S. NSF under Cooperative Agreement No. 1852977. WPS was further supported by Grant NSF AGS-1853929 and NASA Grant 80NSSC24K0706. The ACCLIP GV data were collected using NSF’s Lower Atmosphere Observing Facilities, which are managed and operated by NSF NCAR’s Earth Observing Laboratory. QL is supported by the NASA Upper Atmospheric Composition Observations and Modeling, Analysis and Prediction Programs. The ACCLIP campaign was supported by NSF, NASA, NOAA, and the Office of Naval Research (ONR). The COLD2 deployment was funded by the European Space Agency (ESA) contract QA4EO486 ACCLIP. Open access publication funding provided by COUPERIN CY26.
KeyWords: Asian summer monsoon; carbon monoxide; upper troposphere; IASI; remote sensing; pollution transport
DOI: 10.1029/2025JD045647