Global-scale distribution of ozone in the remote troposphere from ATom and HIPPO airborne field missions

Abstract

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.

Zonal Similarity of Long‐Term Changes and Seasonal Cycles of Baseline Ozone at Northern Midlatitudes

“…After the seasonal variance is remove, only 13% of the total variance remains (i.e., 18.5 ppb 2 ), indicating that the spatial variability and zonally similar seasonal cycles dominate the variance of monthly mean baseline ozone at northern midlatitudes. The northern midlatitude zonal similarity found in this work is consistent with a recent analysis of the ozone observations from the remote troposphere collected during the global HIPPO and ATom airborne field missions (Bourgeois et al, 2020). This study found that the ozone distribution was similar in the extra tropics over the Atlantic and Pacific Oceans in both the Southern and Northern Hemispheres.…”

“…This study found that the ozone distribution was similar in the extra tropics over the Atlantic and Pacific Oceans in both the Southern and Northern Hemispheres. Consistent with the hypothesis guiding this work, Bourgeois et al (2020) attributed the similarity to the zonal circulation of baseline ozone.…”

A Cavity-Enhanced UV Absorption Instrument for High Precision, Fast Time Response Ozone Measurements

“…The DC-8 FIREX-AQ payload included the NOAA Nitrogen Oxides and Ozone (NOyO3) instrument, a well-established O3 225 measurement using the chemiluminescence technique (Ryerson et al, 2000;Bourgeois et al, 2020). ROZE operated simultaneously with the NOyO3 instrument during several flights.…”