Aerosol particles play a critical role in the tropical tropopause layer (TTL) through cloud formation and heterogeneous chemistry, influencing the radiative and chemical balance of the stratosphere. However, aerosol measurements in the TTL are sparse, resulting in poor knowledge of aerosol abundance and distribution in this important region. Here, we present in situ aircraft measurements over the western tropical Pacific, revealing a persistent and altitude-dependent enhancement of aerosol mass in the TTL compared to the convectively influenced troposphere below. Notably, our data demonstrate a striking positive correlation between aerosol mass and ozone. Model simulations suggest that organic materials constitute a substantial fraction of the total aerosol mass within the TTL. We further derived an empirical parameterization of TTL aerosol mass as a function of ozone. Given the relative ease of ozone measurements and modeling, the parameterization provides a promising framework for estimating TTL aerosol abundance and its effects on climate.

Carbonyl sulfide (OCS) is an important atmospheric sulfur species that plays a dominant role in the formation of (non-volcanic) 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 & 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 the main source regions for deep convective lofting and demonstrates ASM entrainment of OCS enriched parcels in the UTLS, allowing evaluation of global model predictions for OCS’s stratospheric influence. The ACCLIP dataset 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.