Spectroscopy Of PHOsgene for evaluating the injection of ChLorine into the Earth's Stratosphere (SOPHOCLES)
Lead Research Organisation:
University of Leicester
Department Name: National Centre for Earth Observation
Abstract
Long-lived anthropogenic Cl-containing species such as chlorofluorocarbons are a source of stratospheric Cl and deplete the ozone layer. The Montreal Protocol has led to reductions in the concentrations of many such species, and the ozone layer is now recovering. However, very short-lived substances (VSLS) with lifetimes <6 months, e.g. dichloromethane (DCM), provide a direct source of inorganic chlorine (Cly) in the lowermost stratosphere. DCM is widely used as a solvent and in the production of foam agents. If emissions are left unchecked (DCM is not controlled by the Protocol), recovery of the ozone layer will be significantly delayed. DCM currently accounts for ~10% of stratospheric Cly, and its contribution is expected to increase significantly in coming decades along with this growth and as Cl from long-lived gases decreases.
Stratospheric Cl input from VSLS is differentiated into two categories: emitted source gases (source gas injection, SGI) and product gases (product gas injection, PGI). Observationally, source gases can be measured directly by aircraft instruments in the upper troposphere, however these don't provide the long-term record needed for monitoring. Satellite measurements can provide global coverage and long-term monitoring of product gases in the UTLS, but not yet any Cl-VSLS source gases. The Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS) measures a number of Cly species, including one of the most important product gases, phosgene (COCl2).
Phosgene is the common intermediate in the atmospheric degradation of the most important Cl-VSLS: DCM, and the less abundant CHCl3 (chloroform) and C2Cl4 (tetrachloroethene). Cl-VSLS PGI estimates are available from model simulations, however the complexity and approximations in faithfully capturing the chemical processes make these extremely challenging. In particular, there is limited information in the literature regarding the yield of phosgene from DCM oxidation in the upper troposphere. ACE-FTS-derived abundances of phosgene in the upper troposphere are higher than calculated by models by a factor of ~3. The positive trend in these ACE-FTS upper tropospheric phosgene concentrations provided the first direct observational evidence of the increase in PGI associated with VSLS.
In order to understand the increasing impact of Cl-VSLS on ozone depletion and to make future predictions, it is important to validate and improve model simulations of source VSLS and product gases in the UTLS. To achieve this, we need to reconcile inconsistencies between model and observations. In this project, we aim to obtain a better understanding of these observations and their uncertainties by providing a complete re-evaluation of phosgene spectroscopy through new laboratory measurements. Accurate quantitative laboratory spectroscopy is fundamental for retrieving abundances of trace gas species from atmospheric spectra recorded by satellite instruments. This work will lead to more robust satellite datasets of phosgene observations in the UTLS, and provide a better constraint on the phosgene PGI associated with Cl-VSLS.
Stratospheric Cl input from VSLS is differentiated into two categories: emitted source gases (source gas injection, SGI) and product gases (product gas injection, PGI). Observationally, source gases can be measured directly by aircraft instruments in the upper troposphere, however these don't provide the long-term record needed for monitoring. Satellite measurements can provide global coverage and long-term monitoring of product gases in the UTLS, but not yet any Cl-VSLS source gases. The Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS) measures a number of Cly species, including one of the most important product gases, phosgene (COCl2).
Phosgene is the common intermediate in the atmospheric degradation of the most important Cl-VSLS: DCM, and the less abundant CHCl3 (chloroform) and C2Cl4 (tetrachloroethene). Cl-VSLS PGI estimates are available from model simulations, however the complexity and approximations in faithfully capturing the chemical processes make these extremely challenging. In particular, there is limited information in the literature regarding the yield of phosgene from DCM oxidation in the upper troposphere. ACE-FTS-derived abundances of phosgene in the upper troposphere are higher than calculated by models by a factor of ~3. The positive trend in these ACE-FTS upper tropospheric phosgene concentrations provided the first direct observational evidence of the increase in PGI associated with VSLS.
In order to understand the increasing impact of Cl-VSLS on ozone depletion and to make future predictions, it is important to validate and improve model simulations of source VSLS and product gases in the UTLS. To achieve this, we need to reconcile inconsistencies between model and observations. In this project, we aim to obtain a better understanding of these observations and their uncertainties by providing a complete re-evaluation of phosgene spectroscopy through new laboratory measurements. Accurate quantitative laboratory spectroscopy is fundamental for retrieving abundances of trace gas species from atmospheric spectra recorded by satellite instruments. This work will lead to more robust satellite datasets of phosgene observations in the UTLS, and provide a better constraint on the phosgene PGI associated with Cl-VSLS.
Organisations
People |
ORCID iD |
| Jeremy Harrison (Principal Investigator) | |
| Daniel Coxon (Researcher) |