Abstract
Abstract. MIPAS thermal limb emission measurements were used to derive vertically resolved profiles of carbon tetrachloride (CCl4). Level-1b data versions MIPAS/5.02 to MIPAS/5.06 were converted into volume mixing ratio profiles using the level-2 processor developed at Karlsruhe Institute of Technology (KIT) Institute of Meteorology and Climate Research (IMK) and Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Astrofísica de Andalucía (IAA). Consideration of peroxyacetyl nitrate (PAN) as an interfering species, which is jointly retrieved, and CO2 line mixing is crucial for reliable retrievals. Parts of the CO2 Q-branch region that overlap with the CCl4 signature were omitted, since large residuals were still found even though line mixing was considered in the forward model. However, the omitted spectral region could be narrowed noticeably when line mixing was accounted for. A new CCl4 spectroscopic data set leads to slightly smaller CCl4 volume mixing ratios. In general, latitude–altitude cross sections show the expected CCl4 features with highest values of around 90 pptv at altitudes at and below the tropical tropopause and values decreasing with altitude and latitude due to stratospheric decomposition. Other patterns, such as subsidence in the polar vortex during winter and early spring, are also visible in the distributions. The decline in CCl4 abundance during the MIPAS Envisat measurement period (July 2002 to April 2012) is clearly reflected in the altitude–latitude cross section of trends estimated from the entire retrieved data set.
Highlights
Carbon tetrachloride (CCl4) is an anthropogenically produced halogen-yielding trace gas and partly responsible for stratospheric ozone depletion
Vertical profiles of CCl4 were retrieved from MIPAS Environmental Satellite (Envisat) limb emission spectra considering various interfering trace gases and with peroxyacetyl nitrate (PAN) playing a important role
A maximum in the tropics connected with higher values of CCl4 below the northern extratropical tropopause is a feature seen in HCFC-22 (Chirkov et al, 2016), where it was associated with the uplift in the Asian monsoon, so CCl4 distributions in this region might have a similar explanation
Summary
Carbon tetrachloride (CCl4) is an anthropogenically produced halogen-yielding trace gas and partly responsible for stratospheric ozone depletion. Previous measurements of stratospheric CCl4 have been performed by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), a cryosampler instrument employed at Frankfurt University, and the balloon-borne version of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-B2). Additional measurements, especially vertically wellresolved ones with global coverage such as satellite measurements from MIPAS, can help to improve the understanding of the atmospheric CCl4 budget and stratospheric lifetime estimate. We compare the results of the MIPAS Envisat CCl4 retrieval with those of ACE-FTS, those of the second balloon-borne MIPAS instrument (MIPAS-B2) and those of cryosampler measurements The Michelson Interferometer for Passive Atmospheric Sounding was one of the instruments aboard the European Environmental Satellite (Envisat). It was launched into a sunsynchronous orbit at an altitude of approximately 800 km on 1 March 2002. Results shown in this publication cover both the FR and the RR period
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