| 29 Jul 2026
Version 8 of IMK/IAA MIPAS reactive nitrogen reservoir gases
Abstract. Version 8 infrared limb emission spectra provided by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat were used to infer global distributions of HNO3, ClONO2, HNO4, and N2O5 in the altitude range from about 6 to 80 km. Here we describe in detail the analysis of the spectral data by means of constrained non-linear least-squares fitting, and provide information about the averaging kernels, the vertical and horizontal resolutions, and the error budgets of the derived trace gas profiles. For HNO3 and N2O5, the error budgets are dominated by systematic errors, mainly spectroscopic uncertainties, in the relevant altitude range, while for HNO4 and ClONO2 they are dominated by spectral noise. This implies that systematic biases of up to 20% and <10% cannot be excluded for HNO3 and N2O5, respectively, while the information about spatial and temporal variability is quite certain. Random uncertainties of HNO4 and ClONO2 can be favourably reduced by averaging, while systematic uncertainties in the order of 3% (ClONO2) and 20% (HNO4) will remain. The vertical resolution is in the order of 2 to 6 km in the lower and middle stratosphere, depending on the species and the atmospheric situation. Besides the four nitrogen reservoir species, we also present NOyas a derived data product. It is constructed from [HNO3] + [ClONO2] + [HNO4] + 2 x [N2O5] + [NO] + [NO2] and characterised in terms of its random and systematic error budget. Along with the regular data product of the four nitrogen reservoir species, an additional representation of the data on a coarser vertical grid is offered. These data can be used without consideration of the averaging kernels. The new trace gas distributions are compared to the previous data version, and they are discussed along the most relevant signatures of processes to be observed. We find that the new data products provide improved consistency between the full- and reduced-resolution mission periods of MIPAS, as well as between the observation modes covering different altitude ranges, and they exhibit all the analysed features caused by known atmospheric processes.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Measurement Techniques.
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