Carbonyl Sulfide (OCS) in the Upper Troposphere/Lowermost Stratosphere (UT/LMS) Region: Estimates of Lifetimes and Fluxes

• Published in: Geophysical research letters Vol. 50; no. 19
• Main Authors: Karu, Einar, Li, Mengze, Ernle, Lisa, Brenninkmeijer, Carl A. M., Lelieveld, Jos, Williams, Jonathan
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.10.2023; Wiley
• Subjects: Aerosol particles; Aerosols; Air sampling; Carbonyl compounds; Carbonyl sulfide; Carbonyls; Climate; Energy balance; Gases; Lifetime; Mixing ratio; Ozone; Passenger aircraft; Stratosphere; Stratospheric sulfate; Sulfates; Sulfides; Sulfur compounds; Sulphides; Sulphur; Sulphur compounds; Trace gases; Troposphere; Upper troposphere
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL105826

Carbonyl sulfide (OCS or COS) is a ubiquitous trace gas and plays a role in forming stratospheric sulfate aerosol particles, thereby influencing climate. In this study, whole‐air samples containing OCS were collected onboard a passenger aircraft (IAGOS‐CARIBIC) from the upper troposphere/lowermost stratosphere (UT/LMS, 10–12 km) region and analyzed with CryoTrap–GC–AED system in the laboratory. Global OCS mixing ratios are presented and by using the OCS measurements in conjunction with other trace gases, an atmospheric OCS lifetime of 2.1 ± 1.3 years, and lowermost stratospheric OCS lifetime of 47 ± 16 years were determined. A total flux of 137 GgS a−1 of OCS from the troposphere into the stratosphere was estimated, and the stratospheric sink estimate yielded 55 ± 23 GgS a−1 of OCS. The 60% smaller sink can be interpreted as 82 GgS a−1 OCS which is transported back from the stratosphere into the troposphere. Plain Language Summary Carbonyl sulfide (OCS) is the most abundant sulfur compound in the atmosphere. Due to its long atmospheric lifetime, OCS can be transported into the stratosphere where it forms a layer of sulfate aerosol particles at 30 km altitude. By reflecting incoming radiation and through perturbing ozone levels this layer has large impact on the Earth's energy balance and therefore climate. In this study, we have determined OCS mixing ratios in air samples collected in the upper troposphere/lowermost stratosphere (UT/LMS, 10–12 km) region from 2015 to 2018. From these measurements we estimated the total atmospheric lifetime and the stratospheric lifetime of OCS to be 2.1 ± 1.3 years, and 47 ± 16 years, respectively. We also estimated the total flux of OCS transported into the stratosphere from the troposphere to be 137 GgS a−1, of which only 40% 55 GgS a−1 remained in the stratosphere, and the remianing 60% (82 GgS a−1) were transported back into the troposphere. Key Points Carbonyl sulfide (OCS) atmospheric lifetime of 2.1 ± 1.3 years and lowermost stratospheric lifetime of 47 ± 16 years were determined Total flux of OCS into the stratosphere estimated as 137 GgS a−1, of which 60% is estimated to be transported back into the troposphere The lower back transport estimate might explain the current missing stratospheric sulfate aerosol burden