An Integrated Analysis of Ozone and Carbon Monoxide Over the Western Pacific Using Satellite and Aircraft Measurements During the ACCLIP Summer Campaign 2022

The western Pacific exhibited a complex interplay of monsoonal dynamics and transport during the Asian Summer Monsoon Chemical & Climate Impact Project (ACCLIP) airborne field campaign in summer 2022. We analyze in situ observations of ozone (O₃) and carbon monoxide (CO) from 29 research flights—profiling over South Korea and cruising over the western Pacific —and balloon soundings in South Korea and Taiwan. In the upper troposphere (UT), a twofold enhancement in CO was observed across the mid-latitudes of the western Pacific, driven by large-scale uplift and outflow associated with the Asian Summer Monsoon (ASM) system. Observational evidence of enhanced UT O₃ in conjunction with its primary precursor, nitrogen dioxide (NO₂), was also presented. Satellite observations from the TROPOspheric Monitoring Instrument (TROPOMI) and Microwave Limb Sounder (MLS) were integrated with two selected flight cases to explore transport events and to provide broader spatial context. On July 31, the ASM anticyclone manifested in two distinct modes, South Asia High (SAH) and Western Pacific High (WPH). The SAH was filled with polluted air masses uplifted from the Asian boundary layer while the WPH was sustained by deep maritime convection. Both flight and satellite data captured polluted air parcels over the tropical western Pacific that had detached from the “main” anticyclonic eddy. By examining the case on August 6, we observed that the western Pacific was strongly modulated by low-level westerlies and the eastward extension of the ASM anticyclone and isentropic mixing near the tropopause.