Highlighting the Impact of Anthropogenic OCS Emissions on the Stratospheric Sulfur Budget With In Situ Observations

Carbonyl sulfide (OCS) is an important atmospheric sulfur species that plays a dominant role in the formation of (nonvolcanic) stratospheric sulfate aerosol in the middle stratosphere. Major uncertainties in surface sources and sinks and inconsistent model representation of vertical transport limit understanding of OCS distribution, particularly in the sparsely sampled upper atmosphere. During the 2022 Asian Summer Monsoon Chemical and CLimate Impact Project (ACCLIP) campaign, in situ measurements of OCS in the Upper Troposphere and Lower Stratosphere (UTLS) at the eastern edge of the Asian summer monsoon anticyclone (ASM), showed significant OCS enhancements (>750 ppt) near the tropopause from convectively influenced air parcels. Here, we compare these novel Asian UTLS measurements with long-term satellite observations and regional measurements to broaden understanding of OCS trends and its transport by the ASM. Trajectory analysis identifies northern China as the main source region for deep convective lofting of OCS-enriched parcels and demonstrates ASM entrainment in the UTLS, allowing evaluation of global model predictions for OCS's stratospheric influence. The ACCLIP data set provides vital in situ validation of limited vertically resolved OCS data in a region of significant anthropogenic emissions, which serves to enhance our understanding of the global sulfur budget.