High-altitude research aircraft measures record-breaking concentrations of ozone-depleting-chlorine over the western Pacific suggesting that the stratospheric chlorine budget may be larger than currently estimated.

The Asian Summer Monsoon (ASM), a significant element of the climate system, has been studied as a regional weather pattern for centuries. Only in recent decades has its role in global constituent transport been recognized, largely owing to observations made from satellites. The ASM is of particular interest because its associated deep convective systems rapidly transport air masses from the planetary boundary layer in one of the most polluted regions on the planet to the stratosphere. As part of the Asian summer monsoon Chemical and Climate Impact Project (ACCLIP), a field campaign, led by NASA and NCAR, conducted in summer 2022 using airborne observations onboard two high-altitude aircraft, an international team of scientists have found that the east Asain summer monsoon injects record-breaking levels of ozone-depleting short-lived chlorine to the stratosphere. The concentrations of short-lived chlorine measured during ACCLIP are more than twice the previously reported observations in the tropical tropopause. Considering the recently observed increase in short-lived emissions and the ongoing strengthening of the east Asian summer monsoon under global warming, the results suggest a 1) reevaluation of the stratospheric chlorine budget and 2) east Asian monsoon convection provides a significant yet overlooked pathway for these anthropogenic ozone-depleting substances to enter the stratosphere. The results are published in PNAS: Laura L. Pan, Elliot L. Atlas, Shawn B. Honomichl, Warren P. Smith, Douglas E. Kinnison, Susan Solomon, Michelle L. Santee, Alfonso Saiz-Lopez, Johannes C. Laube, Bin Wang, Rei Ueyama, Jim F. Bresch, Rebecca S. Hornbrook, Eric C. Apel, Alan J. Hills, Victoria Treadaway, Katie Smith, Sue Schauffler, Stephen Donnelly, Roger Hendershot, Richard Lueb, Teresa Campos, Silvia Viciani, Francesco D’Amato, Giovanni Bianchini, Marco Barucci, James R. Podolske, Laura T. Iraci, Colin Gurganus, Paul Bui, Jonathan M. Dean-Day, Luis Millán, Ju-Mee Ryoo, Barbara Barletta, Ja-Ho Koo, Joowan Kim, Qing Liang, William J. Randel, Troy Thornberry and Paul A. Newman. East Asian summer monsoon delivers large abundances of very-short-lived organic chlorine substances to the lower stratosphere. Proceedings of the National Academy of Sciences.