MIPAS is a Fourier Transform spectrometer that measured the atmospheric limb emission spectra in the middle infrared on board the ENVISAT satellite. These measurements allowed the global monitoring of the three-dimensional (latitude, longitude and altitude) distribution of temperature and of the concentrations of many species, during both day and night, for 10 years, from July 2002 to April 2012. MIPAS measurements allowed to study the atmosphere from the upper troposphere to the stratosphere and above, up to the thermosphere. The interest in these measurements goes beyond the end of the mission, as they can be used in long time series of data to determine changes in atmospheric composition and in our planet's climate. Furthermore, if the Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT) mission, one of four candidates for Earth Explorer 11, will be selected, MIPAS data will constitute a benchmark for these measurements. CAIRT exploits indeed the heritage of MIPAS on ENVISAT, but allows to measure the composition of the atmosphere with unprecedented three-dimensional resolution being the first imaging Fourier Transform spectrometer sounding the limb of the atmosphere from space. For the last reanalysis of the whole MIPAS mission, a significant effort was made by the MIPAS Quality Working Group, supported by ESA, to improve both L1 [1] and L2 processors, as well as spectroscopy and Level 2 Initial Guess profiles [2], with the objectives of obtaining L2 products with increased accuracy, better temporal stability, and a larger number of retrieved species. The main improvements of L1 processor were related to the radiometric calibration and pointing. With these new processors a MIPAS full mission reprocessing has been recently performed ([1] and [3]). The quality of this final operational data set has been assessed with comprehensive validation studies including comparisons to ground-based in-situ and balloon-borne measurements. The dataset containing the new version 8 of both L1 and L2 products and covering the entire MIPAS operational lifetime period (2002-2012) is available at ESA Earth Online web site.This paper will focus on the lessons learnt, on the quality of the reprocessed data, on the remaining problems, and on further improvements that could improve the quality of both MIPAS L1 and L2 datasets.[1] Kleinert et al. Kleinert, A., Birk, M., Perron, G., and Wagner, G.: Level 1b error budget for MIPAS on ENVISAT, Atmos. Meas. Tech., 11, 5657-5672,https://doi.org/10.5194/amt-11-5657-2018, 2018 [2] Raspollini, P., Arnone, E., Barbara, F., Bianchini, M., Carli, B., Ceccherini, S., Chipperfield, M. P., Dehn, A., Della Fera, S., Dinelli, B. M., Dudhia, A., Flaud, J.-M., Gai, M., Kiefer, M., López-Puertas, M., Moore, D. P., Piro, A., Remedios, J. J., Ridolfi, M., Sembhi, H., Sgheri, L., and Zoppetti, N.: Level 2 processor and auxiliary data for ESA Version 8 final full mission analysis of MIPAS measurements on ENVISAT, Atmos. Meas. Tech. Discuss. [preprint], https://doi.org/10.5194/amt-2021-235, in review, 2021. [3] Dinelli, B. M., Raspollini, P., Gai, M., Sgheri, L., Ridolfi, M., Ceccherini, S., Barbara, F., Zoppetti, N., Castelli, E., Papandrea, E., Pettinari, P., Dehn, A., Dudhia, A., Kiefer, M., Piro, A., Flaud, J.-M., Lopez-Puertas, M., Moore, D., Remedios, J., and Bianchini, M.: The ESA MIPAS/ENVISAT Level2-v8 dataset: 10 years of measurements retrieved with ORM v8.22, Atmos. Meas. Tech. Discuss. [preprint], https://doi.org/10.5194/amt-2021-215, accepted, 2021.

High quality long-term data sets of altitude-resolved measurements of the atmospheric composition areimportant because they can be used both to study the evolu-tion of the atmosphere and as a benchmark for future mis-sions. For the final ESA reprocessing of MIPAS (MichelsonInterferometer for Passive Atmospheric Sounding) on ENVISAT (ENViromental SATellite) data, numerous improve-ments were implemented in the Level 2 (L2) processor Op-timised Retrieval Model (ORM) version 8.22 (V8) and itsauxiliary data. The implemented changes involve all aspects of the processing chain, from the modelling of the measure-ments with the handling of the horizontal inhomogeneitiesalong the line of sight to the use of the optimal estimationtechnique to retrieve the minor species, from a more sensitive approach to detecting the spectra affected by cloudsto a refined method for identifying low quality products. Improvements in the modelling of the measurements werealso obtained with an update of the used spectroscopic dataand of the databases providing the a priori knowledge ofthe atmosphere. The HITRAN_mipas_pf4.45 spectroscopic database was finalised with new spectroscopic data verifiedwith MIPAS measurements themselves, while recently measured cross-sections were used for the heavy molecules. TheLevel 2 Initial Guess (IG2) data set, containing the clima-tology used by the MIPAS L2 processor to generate the ini-tial guess and interfering species profiles when the retrieved profiles from previous scans are not available, was improved taking into account the diurnal variation of the profiles defined using climatologies from both measurements and models. Horizontal gradients were generated using the ECMWFERA-Interim data closest in time and space to the MIPASdata. Further improvements in the L2 V8 products derivedfrom the use of the L1b V8 products, which were upgraded to reduce the instrumental temporal drift and to handle theabrupt changes in the calibration gain. The improvements in-troduced into the ORM V8 L2 processor and its upgraded auxiliary data, together with the use of the L1b V8 products, lead to the generation of the MIPAS L2 V8 products, which are characterised by an increased accuracy, better temporal stability and a greater number of retrieved species.

The observations acquired during the full mission of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument, aboard the European Space Agency Environmental Satellite (Envisat), have been analysed with version 8.22 of the Optimised Retrieval Model (ORM), originally developed as the scientific prototype of the ESA level-2 processor for MIPAS observations. The results of the analyses have been included into the MI- PAS level-2 version 8 (level2-v8) database containing atmospheric fields of pressure, temperature, and volume mixing ratio (VMR) of MIPAS main targets H2 O, O3 , HNO3 , CH4 , N2 O, and NO2 , along with the minor gases CFC- 11, ClONO2 , N2 O5 , CFC-12, COF2 , CCl4 , CF4 , HCFC-22, C2 H2 , CH3 Cl, COCl2 , C2 H6 , OCS, and HDO. The database covers all the measurements acquired by MIPAS in the nominal measurement mode of the full resolution (FR) part of the mission (from July 2002 to March 2004) and all the observation modes of the optimised resolution (OR) part (from January 2005 to April 2012). The number of species included in the MIPAS level2-v8 dataset makes it of particular importance for the studies of stratospheric chemistry. The database is considered by ESA the final release of the MIPAS level-2 products.The ORM algorithm is operated at the vertical grid coincident to the tangent altitudes of the observations or to a subset of them, spanning (in the nominal mode) the alti- tude range from 6 to 68km in the FR phase and from 6 to 70 km in the OR period. In the latitude domain, FR profiles are spaced by about 4.7o, while the OR profiles are spaced by about 3.7o. For each retrieved species, the auxiliary data and the retrieval choices are described. Each product is characterised in terms of the retrieval error, spatial resolution, and "useful" vertical range in both phases of the MIPAS mission. These depend on the characteristics of the measurements (spectral and vertical resolution of the measurements), the retrieval choices (number of spectral points in- cluded in the analyses, number of altitudes included in the vertical retrieval grid), and the information content of the measurements for each trace species. For temperature, water vapour, ozone, and nitric acid, the number of degrees of freedom is significantly larger in the OR phase than in the FR one, mainly due to the finer vertical measurement grid. In the FR phase, some trace species are characterised by a smaller retrieval error with respect to the OR phase, mainly due to the larger number of spectral points used in the analyses, along with the reduced vertical resolution. The way of handling possible caveats (negative VMR, vertical grid representation) is discussed. The quality of the retrieved profiles is assessed through four criteria, two providing information on the successful convergence of the retrieval iterations, one on the capability of the retrieval to reproduce the measurements, and one on the presence of outliers. An easy way to identify and filter the problematic profiles with the informa- tion contained in the output files is provided. MIPAS level2- v8 data are available to the scientific community through the ESA portal (https://doi.org/10.5270/EN1-c8hgqx4).

MIPAS is a Fourier Transform spectrometer that measured the atmospheric limb emission spectra in the middle infrared on board the ENVISAT satellite. These measurements allowed the global monitoring of the three-dimensional (latitude, longitude and altitude) distribution of concentrations of many species, during both day and night, for 10 years, from July 2002 to April 2012. Being a limb sounding instrument, the focus of MIPAS measurements was the study of the atmosphere from the upper troposphere to the stratosphere and above, up to the mesosphere. The interest in these measurements goes beyond the end of the mission, as they can be used in long time series of data to determine changes in our planet's climate. To this purpose, it is therefore important to continue improving their quality. The quality of MIPAS L2 products depends on the quality of the L1 products, on the L2 model accuracy, on the quality of auxiliary data, particularly on spectroscopic data. For the last reanalysis of the whole MIPAS mission, a significant effort was made by the MIPAS Quality Working Group, supported by ESA, to improve both L1 and L2 processors, as well as spectroscopy, with the objectives of obtaining L2 products with increased accuracy, better temporal stability, and a larger number of retrieved species. Here we present the full mission dataset, including vertical profiles of 21 trace species plus temperature, obtained by applying the latest version of ESA L2 processor (ORM V8) to the MIPAS L1 data obtained with version 8 of the L1 processor. The impact of the improvements of both L1 and L2 processors on the quality of the L2 products is presented, as well as results of the validation against independent correlative measurements.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a limb-viewing infrared Fourier transform spectrometer that operated from 2002 to 2012 onboard the ENVISAT satellite. The analysis of MIPAS measurements allows to study the temporal evolution of numerous species of interest for the study of the ozone in the stratosphere, pollutants and many green-house gases. The objective of the MIPAS Quality Working Group is to improve the quality of the MIPAS products through a fruitful collaboration among spectroscopists, Level 1, Level 2, and validation teams. A large effort has recently led to implement significant improvements in both ESA Level 1 and Level 2 processors, as well as in spectroscopic database and in some absorption cross-sections in order to improve the quality of the products. In addition to the products already present in the V7 dataset (temperature and the VMR of H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, CFC-12, N2O5, ClONO2, HCFC-22, COF2, CF4, HCN and CCl4), the VMR of six additional species (OCS, CH3Cl, HDO, C2H2, C2H6, COCl2) will be provided in V8 dataset. In order to evaluate the impact of the changes in the products before full mission reprocessing, the analysis of the performances of the products of the modified L1 and L2 processors, as well as the auxiliary data, has been performed on a Diagnostic DataSet (DDS). The orbits of the DDS have been chosen in coincidence with correlative measurements for performing also a preliminary assessment of the accuracy of the products and to evaluate possible changes in the drift. With respect to V7 products, main improvements consist in a reduction of the temperature bias in the first part of the mission, a reduction of the discontinuities in CH4 and N2O time series due to daily gain upgrade, a better filtering of clouds and a better handling of horizontal inhomogeneities.The results of the assessment of the quality of MIPAS measurements will be shown, as well as the study of the temporal evolution and variability of all species. We will also investigate the spatial, seasonal, and interannual variations in the distribution of these species.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a limb-viewing infrared Fourier transform spectrometer that operated from 2002 to 2012 on board the ENVISAT satellite. The fruitful collaboration among spectroscopists, Level 1, Level 2, and validation teams in the frame of the MIPAS Quality Working Group has recently led to the implementation of significant changes in both ESA Level 1 and Level 2 processors, as well as in the spectroscopic database and in some absorption cross-sections. In addition to the products already present in V7 dataset (temperature and the VMR of H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, CFC-12, N2O5, ClONO2, HCFC-22, COF2, CF4, HCN and CCl4), the VMR of six additional species (OCS, CH3Cl, HDO, C2H2, C2H6, COCl2) will be provided in V8 dataset.Among the new species, methyl chloride (CH3Cl) is of great interest in stratospheric ozone chemistry since it is the most abundant chlorine-containing gas in the troposphere and, in contrast to other relatively long-lived ozone-depleting gases, it has both natural and anthropogenic sources, with the known emission being mainly natural (tropical plants, biomass burning, the ocean, salt marshes and fungi). Since it is not controlled under the Montreal Protocol, its importance is expected to increase in the coming decades as emission controls alter the relative contributions from natural and anthropogenic halogen sources.In this paper we present a preliminary assessment of the quality of the MIPAS CH3Cl data, in terms of precision, accuracy and vertical resolution, and we investigate the spatial and seasonal variations in the distribution of CH3Cl in the upper troposphere/lower stratosphere (UTLS).

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a limb-viewing infrared Fourier transform spectrometer that operated from 2002 to 2012 onboard the ENVISAT satellite. The maintenance and the upgrade of both L1 and L2 ESA processors are accomplished by the Quality Working Group, where a fruitful collaboration among Level 1, Level 2 and validation teams can be exploited. Recently both ESA L1 and L2 processors have been updated, as well as the spectroscopic database and some absorption cross-sections. In addition to the products already present in the current release (V7) of ESA MIPAS data (temperature and the VMR of H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, CFC-12, N2O5, ClONO2, HCFC-22, COF2, CF4, HCN and CCl4), the VMR of six additional species (OCS, CH3Cl, HDO, C2H2, C2H6, COCl2) will be provided in V8 dataset. In preparation of V8 full mission reprocessing, three Diagnostic Datasets have been generated to check the performances of all L1, L2 processors and the new auxiliary data.The analysis of these Diagnostic Datasets and the comparison with previous full mission dataset V7 will be used to perform a first assessment of the quality of the new V8 products. In the paper special focus will be given to the new species.