21 Jun 2021

21 Jun 2021

Review status: this preprint is currently under review for the journal AMT.

Phosgene distribution derived from MIPAS ESA v8 data: intercomparisons and trends

Paolo Pettinari1,2, Flavio Barbara3, Simone Ceccherini3, Bianca Maria Dinelli2, Marco Gai3, Piera Raspollini3, Luca Sgheri4, Massimo Valeri5, Gerald Wetzel6, Nicola Zoppetti3, and Marco Ridolfi1,7 Paolo Pettinari et al.
  • 1Dipartimento di Fisica e Astronomia, Università di Bologna, Bologna, Italy
  • 2Istituto di Scienze dell’Atmosfera e del Clima, – CNR, Bologna, Italy
  • 3Istituto di Fisica Applicata “Nello Carrara” del Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy
  • 4Istituto per le Applicazioni del Calcolo “Picone” – CNR, Firenze, Italy
  • 5Serco Italia S.p.A., Frascati (Rome), Italy
  • 6Karlsruhe Institute of Technology – IMK-ASF, Karlsruhe, Germany
  • 7Istituto Nazionale di Ottica – CNR, Firenze, Italy

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measured the middle-infrared limb emission spectrum of the atmosphere from 2002 to 2012 on board ENVISAT, a polar-orbiting satellite. Recently, the European Space Agency (ESA) completed the final reprocessing of MIPAS measurements, using Version 8 of the Level 1 and Level 2 processors, which include more accurate models, processing strategies and auxiliary data. The list of retrieved gases has been extended, it now includes a number of new species with weak emission features in the MIPAS spectral range. The new retrieved trace species include carbonyl chloride (COCl2), also called phosgene. Due to its toxicity, its use has been reduced over the years, however it is still used by chemical industries for sevaeral applications. Besides its direct injection in the troposphere, stratospheric phosgene is mainly produced from the photolysis of CCl4, a molecule present in the atmosphere because of human activity. Since phosgene has a long stratospheric lifetime, it must be carefully monitored as it is involved in the ozone destruction cycles, especially over the winter polar regions.

In this paper we exploit the ESA MIPAS Version 8 data in order to discuss the phosgene distribution, variability and trends in the middle and lower stratosphere and in the upper troposphere.

The zonal averages show that phosgene volume mixing ratio is larger in the stratosphere, with a peak of 40 pptv between 50 and 30 hPa at equatorial latitudes, while at middle and polar latitudes it varies from 10 to 25 pptv. A moderate seasonal variability is observed in polar regions, mostly between 80 and 50 hPa.

The comparison of MIPAS/ENVISAT COCl2 v.8 profiles with the ones retrieved from MIPAS/balloon and ACE-FTS measurements highlights a negative bias of about 2 pptv, mainly in polar and mid-latitude regions. Part of this bias is attributed to the fact that the ESA Level 2 v.8 processor uses an updated spectroscopic database.

For the trend computation, a fixed pressure grid is used to interpolate the phosgene profiles and, for each pressure level, VMR monthly averages are computed in pre-defined 10°-wide latitude bins. Then, for each latitudinal bin and pressure level, a regression model has been fitted to the resulting time-series in order to derive the atmospheric trends.

We find that the phosgene trends are different in the two hemispheres. The analysis shows that the stratosphere of the Northern Hemisphere is characterised by a negative trend, of about −7 pptv/decade, while in the Southern Hemisphere phosgene mixing ratios increase with a rate of the order of +4 pptv/decade. In the upper troposphere a positive trend is found in both hemispheres.

Paolo Pettinari et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-115', Anonymous Referee #1, 18 Jul 2021
  • RC2: 'Comment on amt-2021-115', Anonymous Referee #2, 20 Jul 2021

Paolo Pettinari et al.

Data sets

ACE-FTS Data Peter Bernath, Chris Boone, Tom McElroy

MIPAS ESA Level 2 products version 8 Piera Raspollini, Marco Ridolfi, Luca Sgheri, Marco Gai, Bianca Maria Dinelli, Flavio Barbara, Simone Ceccherini

Paolo Pettinari et al.


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Short summary
Phosgene (COCl2) is a toxic gas whose presence is consequence of human activity. Besides its direct injection in the troposphere, stratospheric COCl2 is produced from the decomposition of CCl4, an anthropogenic gas regulated by the Montreal Protocol. As a consequence, COCl2 negative trends characterize the lower and part of the middle stratosphere. However, we find positive trends in the upper troposphere, demonstrating the non-negligible role of other Cl-containing species not yet regulated.