Climatologies of lower stratospheric NOy and O3 and correlations with N2O based on in situ observations

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Abstract
This paper presents NOy and O3 seasonal mean distributions as a function of equivalent latitude and height from more than 140 ER‐2 flights. The observations span a height range of 360–530 K (∼150‐45 hPa) and have nearly pole‐to‐pole coverage in most seasons. These climatologies are intended to support efforts to evaluate the chemistry and dynamics of assessment models. Reasonable model representations of NOy, O3, and their seasonal variations are necessary to assess the effects of aircraft exhaust on the stratosphere. ER‐2 measurements of N2O are combined with the NOy data to examine their lower stratospheric relationship and to identify regions of denitrification. Measurements of these species above ER‐2 altitudes in the Arctic vortex support the interpretation of some of the ER‐2 NOy‐N2O data, which suggest that transport rather than chemical denitrification causes deviations from the normally linear relationship. This places constraints on the use of a linear relationship to calculate denitrification. The observed relationship between N2O and O3 is also presented. The spatial gradients in lower stratospheric O3 photochemistry are used to explain observed variations in the N2O‐O3 relationship. The N2O‐O3 relationship above ER‐2 altitudes in the Arctic vortex, much like the case of NOy‐N2O, also differs in slope from lower altitudes. This points to the difficulties in using tracer correlations to infer O3 values in the vortex prior to polar stratospheric cloud processing. It is necessary to understand the photochemical and transport history of the air that descends into the lower stratospheric vortex in order to correctly quantify O3 depletion.