Stratospheric ozone intrusions over the northwest Atlantic: Multiseasonal cases from the ACTIVATE airborne mission
Brooke Beran1, Leong Wai Siu1, Yonghoon Choi2,3, Joshua DiGangi2, Glenn S. Diskin2, Kenneth L. Thornhill2,3, Keming Pan1, Avelino Arellano1 and Armin Sorooshian1,4*
1Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, 85721, USA
2NASA Langley Research Center, Hampton, VA, 23681, USA
3Analytical Mechanics Associates, Inc., Hampton, VA, 23666, USA
4Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ, 85721, USA
Abstract
Stratospheric intrusions (SIs) can greatly influence tropospheric ozone (O3) concentrations, with consequences for human health, the environment, and climate change. Fifteen SI cases are identified over the U.S. East Coast and Bermuda using airborne data from the Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) in multiple seasons between 2020-2022. SI identification is based on the following criteria from in-situ measurements and trajectory calculations: O3 >70 ppbv, carbon monoxide <120 ppb, methane <1.97 ppm, relative humidity <20%, and maximum altitude reached during TRAJ3D back-trajectories exceeding the ERA-5 tropopause height. The flight maximum O3 values (70.7-121.7 ppbv) for the 15 SIs were detected between flight altitudes of 1.3-6.5 km. Flights are sorted into different altitude bins (0-1 km, 1-4 km, 4-7 km) to compare SI and non-SI flight O3 concentrations, as well as surface (0-1 km) and free tropospheric (>1 km) O3 values on the same SI-influenced flight. Across the SI cases, O3 near the surface is lower than flight maximum O3 values by an average of 44.1 ppbv. During SI flights, O3 concentrations in a given altitude bin are on average 33.4 ppbv higher than monthly median non-SI flight O3 values within the same altitude bin. Additionally, the relationship between flight maximum O3 and time elapsed from when air associated with the SIs originates above the ERA-5 tropopause is suggestive of an exponential decay. This study provides key insights into characteristics and origins of SIs and how airborne data can be used to better understand these cases.