The balloonborne SPIRALE (a French acronym for infrared absorption spectroscopy by tunable diode lasers) instrument has been developed for in situ measurements of several tracer and chemically active species in the stratosphere. Laser absorption takes place in an open Herriott multipass cell located under the balloon gondola, with six lead salt diode lasers as light sources. One mirror is located at the extremity of a deployable mast 3.5 m below the gondola, enabling the measurement of very low abundance species throughout a very long absorption path (up to 544 m). Three successful flights have produced concentration measurements of O3, CO, CO2, CH4, N2O, NO2, NO, HNO3, HCl, HOCl, COF2, and H2O2. Fast measurements (every 1.1 s) allow one to obtain a vertical resolution of 5 m for the profiles. A detection limit of a few tens of parts per trillion in volume has been demonstrated. Uncertainties of 3%-5% are estimated for the most abundant species rising to about 30% for the less abundant ones, mainly depending on the laser linewidth and the signal-to-noise ratio.
Simultaneous measurements of NO2, O3, NO3, and aerosol extinction coefficient vertical distribution have been made in the middle of the night by the AMON (Absorption par Minoritaires Ozone et Nox) instrument on October 16, 1993, from a balloon platform at float altitude, above Aire sur l'Adour in the south of France. Amon measures atmospheric transmission in the UV Visible range, using the star occultation method. Vertical distributions, obtained between 20 and 40 km, are calculated by a tangent ray inversion technique. Measurements of NO and NO2 by the HALOE (HALogen Occultation Experiment) instrument aboard UARS were also available on October 17, 1993, close to Aire sur l'Adour. Comparison with box model simulations, including heterogeneous reactions, shows that while an increase of NO3 concentration at 38 km could be explained by an occasionally steep vertical gradient of temperature concentrations, another increase of both NO2 and NO3 measured by AMON between 22 to 25 km, i.e. in the upper part of the aerosol layer, cannot be explained by the model. Such an increase is also present on one HALOE profile close to Aire sur l'Adour, for the same altitude range.
Abstract. In this paper we study the impact of the modelling of N 2 O on the simulation of NO 2 and HNO 3 by comparing in situ vertical profiles measured at mid-latitudes with the results of the Reprobus 3-D CTM (Three-dimensional Chemical Transport Model) computed with the kinetic parameters from the JPL recommendation in 2002. The analysis of the measured in situ profile of N 2 O shows particular features indicating different air mass origins. The measured N 2 O, NO 2 and HNO 3 profiles are not satisfyingly reproduced by the CTM when computed using the current 6-hourly ECMWF operational analysis. Improving the simulation of N 2 O transport allows us to calculate quantities of NO 2 and HNO 3 in reasonable agreement with observations. This is achieved using 3-hourly winds obtained from ECMWF forecasts. The best agreement is obtained by constraining a one-dimensional version of the model with the observed N 2 O. This study shows that the modelling of the NO y partitioning with better accuracy relies at least on a correct simulation of N 2 O and thus of total NO y .
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