ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-4861-2011 Measurement from sun-synchronous orbit of a reaction rate controlling the diurnal NO<sub>x</sub> cycle in the stratosphere Walker J. C. 1 Dudhia A. 1 Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, University of Oxford, Oxford, OX1 3PU, UK 24 05 2011 11 10 4861 4872 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/4861/2011/acp-11-4861-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/4861/2011/acp-11-4861-2011.pdf

A reaction rate associated with the nighttime formation of an important diurnally varying species, N<sub>2</sub>O<sub>5</sub>, is determined from MIPAS-ENVISAT. During the day, photolysis of N<sub>2</sub>O<sub>5</sub> in the stratosphere contributes to nitrogen-catalysed ozone destruction. However, at night concentrations of N<sub>2</sub>O<sub>5</sub> increase, temporarily sequestering reactive NO<sub>x</sub> NO and NO<sub>2</sub> in a natural cycle which regulates the majority of stratospheric ozone. In this paper, the reaction rate controlling the formation of N<sub>2</sub>O<sub>5</sub> is determined from this instrument for the first time. The observed reaction rate is compared to the currently accepted rate determined from laboratory measurements. Good agreement is obtained between the observed and accepted experimental reaction rates within the error bars.

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