Global-scale distribution of ozone in the remote troposphere from the ATom and HIPPO airborne field missions
Authors: Bourgeois Ilann , Peischl Jeff , 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: September 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; four deployments in 2016–2018) and the HIAPER Pole-to-Pole
Observations (HIPPO; five deployments in 2009–2011) experiments, two
global-scale airborne campaigns covering the Pacific and Atlantic basins. ATom and HIPPO represent the first global-scale, vertically resolved
measurements of O3 distributions throughout the troposphere, with HIPPO
sampling the atmosphere over the Pacific and ATom sampling both the Pacific
and Atlantic. 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 from these two campaigns to confirm and extend the existing
knowledge 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 and consistent with previous
modeling and satellite studies. We also show that the ozone distribution
below 8 km was similar in the extra-tropics of the Atlantic and Pacific
basins, likely due to zonal circulation patterns. However, twice as much
ozone was found in the tropical Atlantic as in the tropical Pacific, due
to well-documented dynamical patterns transporting continental air masses
over the Atlantic. Finally, we show that the seasonal variability of
tropospheric ozone over the Pacific and the Atlantic basins is driven
year-round by transported continental plumes and photochemistry, and the
vertical distribution is driven by photochemistry and mixing with
stratospheric air. This new dataset provides additional constraints for
global climate and chemistry models to improve our understanding of both
ozone production and loss processes in remote regions, as well as the
influence of anthropogenic emissions on baseline ozone.