Consistent estimates of carbonyl sulfide and methane stratospheric lifetimes retrieved from AirCore profiles at different latitudes

Abstract

Stratospheric loss is a major sink for both carbonyl sulfide (COS) and methane (CH 4 ), but their stratospheric lifetimes and sinks remain poorly constrained because high-resolution observations of their vertical distributions in the lower stratosphere are sparse. Here, we estimate the mean stratospheric lifetime and sink of COS and CH 4 from their correlations with N 2 O using two distinct methods applied to AirCore vertical profile measurements from three Northern Hemisphere summer campaigns. From these profiles, we derive a COS stratospheric lifetime of 69–90 years, corresponding to a sink of 30–41 GgS yr −1 . For CH 4 ,we find a stratospheric lifetime of 149–168 years, corresponding to a sink of 23–26 TgC yr −1 . These values are in good agreement with previous estimates (39–76 years for COS, 152–160 years for CH 4 ) and with estimates based on ACE-FTS observations (75–76 years for COS, 146–172 years for CH 4 ). As has been noted previously, we also find a decline in the COS tropospheric burden between 2016 and 2020 in our AirCore samples, in contrast to the continued growth of CH 4 and N 2 O. In addition, we found that tracer-tracer correlations vary among flights, and even within the same campaign, pointing to variability in lower-stratospheric composition. Although this variability may reflect differences in stratospheric transport, its origin remains unclear and requires further investigation. These results provide observational constraints on the stratospheric budgets of COS and CH 4 and help refine their representation in atmospheric chemistry and transport models.