Global-scale distribution of ozone in the remote troposphere from ATom and HIPPO airborne field missions
Authors: Bourgeois Ilann , Peischl Jeffrey , Thompson Chelsea R. , Aikin Kenneth C. , Campos Teresa , Clark Hannah , Commane Róisín , Daube Bruce , Diskin Glenn W. , Elkins James W. , Gao Ru-Shan , Gaudel Audrey , Hintsa Eric J. , Johnson Bryan J. , Kivi Rigel , McKain Kathryn , Moore Fred L. , Parrish David D. , Querel Richard , Ray Eric , Sánchez Ricardo , Sweeney Colm , Tarasick David W. , Thompson Anne M. , Thouret Valérie , Witte Jacquelyn C. , Wofsy Steve C. , Ryerson Thomas B. 
Published: April 2020

Abstract. Ozone is a key constituent of the troposphere where it drives photochemical processes, impacts air quality, and acts as a climate forcer. Large-scale in situ observations of ozone commensurate with the grid resolution of current Earth system models are necessary to validate model outputs and satellite retrievals. In this paper, we examine measurements from the Atmospheric Tomography (ATom, 4 deployments in 2016–2018) and the HIAPER Pole-to-Pole Observations (HIPPO; 5 deployments in 2009–2011) experiments, two global-scale airborne campaigns covering the Pacific (HIPPO and ATom) and Atlantic (ATom) basins. ATom and HIPPO represent the first global-scale, vertically resolved measurements of O3 distributions throughout the troposphere, with HIPPO sampling the Pacific basin and ATom sampling both the Pacific and Atlantic basins. Given the relatively limited temporal resolution of these two campaigns, we first compare ATom and HIPPO ozone data to longer-term observational records to establish the representativeness of our dataset. We show that these two airborne campaigns captured on average 53, 54, and 38 % of the ozone variability in the marine boundary layer, free troposphere, and upper troposphere/lower stratosphere (UTLS), respectively, at nine well-established ozonesonde sites. Additionally, ATom captured the most frequent ozone concentrations measured by regular commercial aircraft flights in the northern Atlantic UTLS. We then use the repeated vertical profiles carried out during these two campaigns to provide a global-scale picture of tropospheric ozone spatial and vertical distributions throughout the remote troposphere. We highlight a clear hemispheric gradient, with greater ozone in the northern hemisphere consistent with greater precursor emissions. We also show that the ozone distribution below 8 km was similar in the extra-tropics of the Atlantic and Pacific basins due to zonal circulation patterns. However, twice as much ozone was found in the tropical Atlantic than in the tropical Pacific, due to well-documented dynamical patterns transporting continental air masses over the Atlantic. We finally show that the seasonal variability of tropospheric ozone over the Pacific and the Atlantic basins is driven by transported continental plumes and photochemistry, and the vertical distribution is driven by photochemistry and mixing with stratospheric air. This new dataset is essential for improving our understanding of both ozone production and loss processes in remote regions, as well as the influence of anthropogenic emissions on baseline ozone.