Abstract
Carbon tetrachloride (CCl4) is one of the species regulated by the Montreal Protocol on account of its ability to deplete stratospheric ozone. As such, the inconsistency between observations of its abundance and estimated sources and sinks is an important problem requiring urgent attention (Carpenter et al., 2014) [5]. Satellite remote-sensing has a role to play, particularly limb sounders which can provide vertical profiles into the stratosphere and therefore validate stratospheric loss rates in atmospheric models.This work is in two parts. The first describes new and improved high-resolution infra-red absorption cross sections of carbon tetrachloride/dry synthetic air over the spectral range 700–860cm−1 for a range of temperatures and pressures (7.5–760Torr and 208–296K) appropriate for atmospheric conditions. This new cross-section dataset improves upon the one currently available in the HITRAN and GEISA databases. The second describes a new, preliminary ACE-FTS carbon tetrachloride retrieval that improves upon the v3.0/v3.5 data products, which are biased high by up to ~20–30% relative to ground measurements. Making use of the new spectroscopic data, this retrieval also improves the microwindow selection, contains additional interfering species, and utilises a new instrumental lineshape; it will form the basis for the upcoming v4.0 CCl4 data product.
Highlights
A clear, colourless, sweet-smelling liquid at room temperature, carbon tetrachloride (CCl4; known as tetrachloromethane or CFC-10) was first synthesised in 1839 from chloroform and chlorine gas by Henry Victor Regnault [1]
This had no effect on the largest industrial application of carbon tetrachloride in the twentieth century, its use as a feedstock in the production of trichlorofluoromethane (CFC-11) and dichlorodifluoromethane (CFC-12), which were commercialised in the 1930s as nonflammable and non-toxic refrigerants [2]
New high-resolution IR absorption cross sections for air-broadened carbon tetrachloride have been determined over the spectral range 700–860 cmÀ1, with an estimated uncertainty of $ 3%
Summary
A clear, colourless, sweet-smelling liquid at room temperature, carbon tetrachloride (CCl4; known as tetrachloromethane or CFC-10) was first synthesised in 1839 from chloroform and chlorine gas by Henry Victor Regnault [1]. The aim of the present work was to improve the ACE-FTS CCl4 retrieval and minimise this high bias This problem has been attacked on two fronts: (1) through the utilisation of new laboratory spectroscopic measurements of air-broadened CCl4 samples over a range of atmospheric pressure-temperature (PT) combinations and; (2) through improvements in the retrieval itself, in particular improved microwindow selection (the avoidance of spectral regions associated with poor or inadequate line parameters of interfering species), the inclusion of new interfering species, and a new instrumental lineshape (ILS). This new scheme will form the basis for the upcoming processing version 4.0 of ACE-FTS data.
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