Phosgene in the UTLS: seasonal and latitudinal variations from MIPAS observations

Valeri, Massimo; Carlotti, M.; Flaud, J.-M.; Raspollini, Piera; Ridolfi, Marco; Dinelli, B. M.

doi:10.5194/amt-9-4655-2016

Cited by 10 publications

(11 citation statements)

References 28 publications

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“…It was noted in the original ACE‐FTS study (Fu et al, ) that the phosgene retrieval uncertainty is dominated by spectroscopic errors, assumed to be ∼30%, resulting from uncertainties in line intensities and the lack of hot bands in the linelist. A recent MIPAS phosgene data set (Valeri et al, ) used a new and improved spectroscopic linelist for phosgene. The upper tropospheric values are comparable to those of the ACE‐FTS, although it needs to be recognized that this was an optimal‐estimation scheme making use of ACE‐FTS profiles as the a priori.…”

Section: Resultsmentioning

confidence: 99%

“…The first global distribution of phosgene was derived from measurements by the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE‐FTS)—in total 5,614 vertical profiles between February 2004 and May 2006 were used (Fu et al, ). More recently Valeri et al () used Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurements, in particular 28,000 vertical profiles from the 18th and 20th of each month of 2008, to investigate the seasonality and latitudinal distribution of phosgene in the UTLS region.…”

Section: Introductionmentioning

confidence: 99%

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Phosgene in the Upper Troposphere and Lower Stratosphere: A Marker for Product Gas Injection Due to Chlorine‐Containing Very Short Lived Substances

Harrison

Chipperfield

Hossaini

et al. 2019

Geophysical Research Letters

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Phosgene in the atmosphere is produced via the degradation of carbon tetrachloride, methyl chloroform, and a number of chlorine‐containing very short lived substances (VSLS). These VSLS are not regulated by the Montreal Protocol even though they contribute to stratospheric ozone depletion. While observations of VSLS can quantify direct stratospheric source gas injection, observations of phosgene in the upper troposphere/lower stratosphere can be used as a marker of product gas injection of chlorine‐containing VSLS. In this work we report upper troposphere/lower stratosphere measurements of phosgene made by the ACE‐FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) instrument and compare with results from the TOMCAT/SLIMCAT three‐dimensional chemical transport model to constrain phosgene trends over the 2004–2016 period. The 13‐year ACE‐FTS time series provides the first observational evidence for an increase in chlorine product gas injection. In 2016, VSLS accounted for 27% of modeled stratospheric phosgene, up from 20% in the mid‐2000s.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Phosgene in the Upper Troposphere and Lower Stratosphere: A Marker for Product Gas Injection Due to Chlorine‐Containing Very Short Lived Substances

Harrison

Chipperfield

Hossaini

et al. 2019

Geophysical Research Letters

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“…Due to the lower intensity of the measured signal, the individual MIPAS spectra show a lower signal to noise ratio (SNR) than the ACE-FTS ones. Despite the larger noise error of the MIPAS profiles retrieved from single scans, Valeri et al (2016) showed that high-vertical-resolution, goodquality distributions of COCl 2 can be obtained by MIPAS on a per profile basis. Therefore, Valeri et al (2016) were able to study the seasonality and the latitudinal distribution of phosgene based on a restricted set of MIPAS measurements: the data acquired over 2 d month −1 in the year 2008.…”

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confidence: 95%

“…For the estimation of global data and trends, the ACE-FTS sparse spatial sampling makes the averaging of the occultation data for periods of several months necessary, both to reduce the random error down to acceptable levels and to enhance the density of its coverage. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) covers the spectral region where phosgene signatures are present; therefore, its measurements can also be used to retrieve the phosgene vertical distribution (Valeri et al, 2016). MIPAS measured the middle-infrared limb emission spectrum of the atmosphere on board the European Space Agency (ESA) Environmental Satellite (EN-VISAT) from 2002 to 2012.…”

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confidence: 99%

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

et al. 2021

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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, and 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 several 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 (parts per trillion by volume) 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 v8 profiles with the ones retrieved from MIPAS balloon and ACE-FTS (Atmospheric Chemistry Experiment – Fourier Transform Spectrometer) 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 v8 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 (volume mixing ratio) 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 characterized by a negative trend of about −7 pptv per decade, while in the Southern Hemisphere phosgene mixing ratios increase with a rate of the order of +4 pptv per decade. This behavior resembles the stratospheric trend of CCl4, which is the main stratospheric source of COCl2. In the upper troposphere a positive trend is found in both hemispheres.

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“…Note that, due to recent updates in the MWMAKE algorithm and in its assumed error figures (Dudhia, 2019), the selected MWs are different from those used in the work of Valeri et al (2016). The selection process of the new MWs has removed the strong interference with the CFC−11 emissions found by Valeri et al (2016), enabling the retrieval of COCl 2 as a single target. The optimised vertical retrieval range for COCl 2 has been estimated to be from 6 to 36 km for the FR measurements and from 9 to 54 km for the OR measurements.…”

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confidence: 99%

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

Pettinari

Barbara

Ceccherini

et al. 2021

Preprint

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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.

show abstract

Phosgene in the UTLS: seasonal and latitudinal variations from MIPAS observations

Cited by 10 publications

References 28 publications

Phosgene in the Upper Troposphere and Lower Stratosphere: A Marker for Product Gas Injection Due to Chlorine‐Containing Very Short Lived Substances

Phosgene in the Upper Troposphere and Lower Stratosphere: A Marker for Product Gas Injection Due to Chlorine‐Containing Very Short Lived Substances

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

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

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