Upper-Tropospheric pollution transport by the Asian Summer Monsoon from IASI observations

The Asian Summer Monsoon (ASM) plays a major role in lifting surface pollutants into the upper troposphere, influencing air quality and climate at regional and global scales. We use 17 years (2007-2023) of carbon monoxide (CO) satellite observations from the Infrared Atmospheric Sounding Interferometer (IASI) to study variability in the ASM region. Seasonal cycles, long-term changes, and dynamical processes such as eddy shedding are analyzed to understand how pollution is transported within and beyond the ASM anticyclone.IASI measurements show good agreement with aircraft observations from the 2022 Asian Summer Monsoon Chemical and CLimate Impact Project (ACCLIP) campaign, confirming the reliability of satellite data for assessing pollution in the upper troposphere. Climatological CO patterns reveal persistent enhancements associated with ASM circulation features, demonstrating IASI’s ability to capture monsoon dynamics over extended periods. Two case studies using IASI observations illustrate upper-tropospheric CO transport from the ASM: the first, supported by GEOS-FP (Goddard Earth Observing System – Forward Processing) simulations, shows consistent spatial structures over the Western Pacific during quiet and eddy shedding periods, while the second highlights how eddy shedding drives long-range transport of ASM-sourced CO across the Pacific towards North America.These findings emphasize the value of long-term satellite observations for tracking upper-tropospheric pollution and understanding its regional and global impacts.