Atmospheric emissions of carbon tetrachloride (CCl4) are regulated by the Montreal Protocol due to its role as a strong ozone-depleting substance. The molecule has been the subject of recent increased interest as a consequence of the so-called "mystery of CCl4", the discrepancy between atmospheric observations and reported production and consumption. Surface measurements of CCl4 atmospheric concentrations have declined at a rate almost 3 times lower than its lifetime-limited rate, suggesting persistent atmospheric emissions despite the ban. In this paper, we study CCl4 vertical and zonal distributions in the upper troposphere and lower stratosphere (including the photolytic loss region, 70-20 hPa), its trend, and its stratospheric lifetime using measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), which operated onboard the ENVISAT satellite from 2002 to 2012. Specifically, we use the MIPAS data product generated with Version 7 of the Level 2 algorithm operated by the European Space Agency. The CCl4 zonal means show features typical of long-lived species of anthropogenic origin that are destroyed primarily in the stratosphere, with larger quantities in the troposphere and a monotonic decrease with increasing altitude in the stratosphere. MIPAS CCl4 measurements have been compared with independent measurements from other satellite and balloon-borne remote sounders, showing a good agreement between the different datasets. CCl4 trends are calculated as a function of both latitude and altitude. Negative trends of about -10 to -15 pptv decade-1 (-10 to -30 % decade-1) are found at all latitudes in the upper troposphere-lower stratosphere region, apart from a region in the southern midlatitudes between 50 and 10 hPa where the trend is positive with values around 5-10 pptv decade-1 (15-20 % decade-1). At the lowest altitudes sounded by MIPAS, we find trends consistent with those determined on the basis of long-term ground-based measurements (-10 to -13 pptv decade-1). For higher altitudes, the trend shows a pronounced asymmetry between the Northern and Southern hemispheres, and the magnitude of the decline rate increases with altitude. We use a simplified model assuming tracer-tracer linear correlations to determine CCl4 lifetime in the lower stratosphere. The calculation provides a global average lifetime of 47 (39-61) years, considering CFC-11 as the reference tracer. This value is consistent with the most recent literature result of 44 (36-58) years.

The Optimized Retrieval Code (ORM) was originally designed to be the scientific code used as the reference for the ESA operational Near Real Time Analysis of MIPAS measurements on ENVISAT. After the end of ENVISAT mission, occurred on April 2017, this code has been adapted and improved to perform the reanalysis of the full MIPAS mission.

MIPAS on ENVISAT performed almost continuous and global measurements of atmospheric temperature and composition from June 2002 to April 2012. These data are very useful for understanding atmosphere climatology from the upper troposphere to the mesosphere, including trends in composition and variability, as a reference for middle atmosphere ozone and general circulation as well as improvement of tropospheric composition retrievals. The ESA Level 2 processor, based on the Optimized Retrieval Model (ORM), originally designed for the Near Real Time analysis and developed by an European Consortium led by IFAC, is currently improved and used for the reanalysis of the full MIPAS mission. The maintenance and the upgrade of the ESA processor are made in the frame of the MIPAS Quality Working Group, where a fruitful collaboration among Level 1, Level 2 and validation teams is exploited. This collaboration is essential to improve the accuracy of the products and their characterization. This paper is meant to describe the most recent upgrades in the MIPAS processor, in particular the full mission was recently reprocessed with L1 V7 and L2 V7 processors, containing significant improvements with respect to previous version 6, and further improvements are in preparation, that will be collected in version 8 of the ESA processor. The improvements include both L1 and L2 processors, as well as the auxiliary data. In the L1 processor the correction of the instrumental drift caused by the ageing of the detectors has been implemented in order to reduce the non negligible systematic error in the trend estimation. Furthermore, the measured daily gain instead of the weekly gain is now used for the radiometric calibration that allows to better take account for the discontinuities in the gain that occasionally occur in MIPAS band B. Improvements in the L2 processor include a different approach for retrieving atmospheric continuum, the use of an a posteriori regularization with altitude dependent constraint, a better approach for handling interfering species, a reduced bias in CFC-11, the handling of horizontal inhomogeneities and the use of ECMWF altitude/pressure relation to determine more accurate altitudes. Improvements in the auxiliary data consist in the use of microwindows with larger information content, an improved spectroscopic database and diurnally varying climatological dataset. Furthermore, additional species are provided in the new processors, leading to a total of 22 retrieved species by the L2 version 8 processor. Each of these changes has a different impact on the Level 2 products. The individual contributions, as well as the cumulative effects, will be evaluated with a comparison with previous versions of MIPAS products and corresponding results of validation. Improvements in the trend determination will also be evaluated, as well as the quality of the new retrieved species.

Carbon tetrachloride (CCl?) is a strong ozone-depleting atmospheric gas regulated by the Montreal protocol. Recently it received increasing interest because it was found that at the surface its atmospheric concentration declines with a rate almost three times smaller than its lifetime-limited rate. Indeed there is a discrepancy between atmospheric observations and the estimated distribution based on the reported production and consumption (the so called "mystery of CCl?"). We use for the first time the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurements to estimate CCl? distribution, its trend, and atmospheric lifetime in the upper troposphere / lower stratosphere (UTLS) region. In particular, here we use MIPAS product generated with Version 7 of the Level 2 algorithm operated by the European Space Agency. The CCl? zonal means show features typical of long-lived species of anthropogenic origin that are destroyed primarily in the stratosphere: larger amounts are found in the troposphere, monotonically decreasing with altitude. We calculate CCl? trends as a function of both latitude and altitude: negative trends are found at all latitudes in the UTLS, apart from a region in the Southern mid-latitudes between 50 and 10 hPa where the trend is slightly positive. At the lowest altitudes sounded by the MIPAS scan we find trend values consistent with those determined on the basis of long-term ground-based measurements. CCl? global average lifetime of 46(38 - 60) years has been estimated using the tracer-tracer linear correlations approach and the CFC-11 as the reference tracer. This estimated value is consistent with the most recent literature result of 44(36 - 58) years.

Atmospheric emissions of Carbon tetrachloride CCl4 are regulated by the Montreal Protocol due to its role as a strong ozone-depleting substance. The molecule has been the subject of recent increased interest as a consequence of the so called ``mystery of CCl4,'' the discrepancy between atmospheric observations and reported production and consumption. Surface measurements of CCl4 atmospheric concentrations have declined at a rate almost three times smaller than its lifetime-limited rate, suggesting persistent atmospheric emissions despite the ban. In this paper, we study CCl4 vertical and zonal distributions in the upper troposphere and lower stratosphere (including the photolytic loss region, 70-20 hPa), its trend, and its stratospheric lifetime using measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), which operated onboard the ENVISAT satellite from 2002 to 2012. Specifically, we use the MIPAS data product generated with Version 7 of the Level 2 algorithm operated by the European Space Agency.The CCl4 zonal means show features typical of long-lived species of anthropogenic origin that are destroyed primarily in the stratosphere, with larger quantities in the troposphere and a monotonic decrease with increasing altitude in the stratosphere. In the troposphere, the largest concentrations are observed at the latitudes of major industrial countries (20/50°N). The good agreement we find between MIPAS CCl4 and independent measurements from other satellite and balloon-borne remote sounders proves the reliability of the MIPAS dataset.CCl4 trends are calculated as a function of both latitude and altitude. Negative trends are found at all latitudes in the upper-troposphere / lower-stratosphere region, apart from a region in the Southern mid-latitudes between 50 and 10 hPa where the trend is positive. At the lowest altitudes sounded by MIPAS, we find trends consistent with those determined on the basis of long-term ground-based measurements. For higher altitudes, the trend shows a pronounced asymmetry between Northern and Southern Hemispheres, and the magnitude of the decline rate increases with altitude. At 50 hPa the decline is about 30-35 %/decade, close to the lifetime-limited trend.We use a simplified model assuming tracer-tracer linear correlations to determine CCl4 lifetime in the lower stratosphere. The calculation provides a global average lifetime of 46(38-60) years considering CFC-11 as the reference tracer. This value is consistent with the most recent literature result of 44(36-58) years.

MIPAS on ENVISAT performed almost continuous measurements of atmospheric composition for approximately 10 years, from June 2002 to April 2012. ESA processor, based on the algorithm ORM (Optimized Retrieval Model), originally designed for the Near Real Time analysis and developed by an European Consortium led by IFAC, is currently used for the reanalysis of the full MIPAS mission. The maintenance and the upgrade of the ESA processor are made in the frame of the Quality Working Group, where a fruitful collaboration among Level 1, Level 2 and validation teams can be exploited. This collaboration is essential to pursue improvements in the accuracy of the products and their characterization. This paper is meant to describe the most recent upgrades in the ESA processor performed to improve the quality of ESA products. In particular, the full mission was recently reprocessed with L1 V7 and L2 V7 processors, containing significant improvements with respect to previous version V6, and further improvements are in preparation, that will be collected in version 8 of the ESA processor. Improvements involve both L1 and L2 processors, as well as the auxiliary data. Improvements in the L1 processor consist in a correction of the instrumental drift, improved spike detection algorithm and new Instrument Line Shape, as well as the use of measured daily gain instead of weekly gain. Improvements in the L2 processor include a different approach for retrieving atmospheric continuum, the use of an a posteriori regularization with altitude dependent constraint, a better approach for handling interfering species, a reduced bias in CFC-11, the handling of horizontal inhomogeneities and the use of ECMWF altitude/pressure relation for determining more accurate altitudes. Improvements in the auxiliary data consist in the use of microwindows with larger information content, new spectroscopic database and diurnally varying climatological dataset. Furthermore, with each new version additional species are provided, leading to 20 the number of retrieved species by the L2 V8 processor. Improvements in the V7 products will be revised on the light of the results of the validation with correlative measurements, and, by comparing the first new L2 V8 products with the L2 V7 ones, a preliminary assessment of the performance of the new V8 processor will be performed.

MIPAS on ENVISAT performed almost continuously measurements of the atmospheric composition for almost 10 years, from June 2002 to April 2012. These ten years cover a period when the first effect of the dismiss of the emission of the CFCs after the Montreal protocol ratification in 1987can be measured. Even if ten years constitute a short period to derive trends, it has been proven that useful information on time variation of atmospheric constituents can be derived from the analysis of these measurements. However, previous versions of MIPAS on ENVISAT dataset were characterized by an instrumental drift due to the fact that some detectors used by MIPAS were affected by non-linearities, which change with time due to the ageing of the detectors and this was cause of a non negligible systematic error in the trend estimation. The new full mission reprocessed dataset V7 that will be released very soon uses L1 files where the impact of the ageing of the detectors on non-linearities has been corrected. Furthermore, also the L2 processor has been upgraded with new functionalities improving the performances of the processor. We present the results of study of trends derived from the analysis of the new MIPAS V7 products on several MIPAS target species including ozone depleting species, like CFC-11, CFC-12, CCl4 and HCFC-22.