Impact of atomic chlorine on the modelisation of total methane and δ13C isotopic signature in LMDz
Abstract
Methane (CH4) is the second strongest anthropogenic greenhouse gas after carbon dioxide (CO2) and is responsible of about 20% of the warming induced by long-lived greenhouse gases since pre-industrial times. Oxidation by the radical hydroxyl OH is the dominant atmospheric sink for methane, contributing to approximately 90% of the total methane mass loss. Chemical losses by atomic oxygen (O1D) and chlorine radicals (Cl) in the stratosphere are other sinks, contributing to about 3% of the total loss. Besides, the chlorine reaction is very fractioning, thus having a much larger impact on δ13C - CH4 isotopic values than on the global methane loss. In this presentation, we assess the impact of atomic chlorine on methane atmospheric loss and on δ13C - CH4, with a focus on the stratosphere where discrepancies between model simulations and observations have been previously noted. Observations used here consist in methane vertical profiles obtained using Aircores samplers above Trainou/Orleans in France. The global circulation model (GCM) LMDz, coupled to a chemistry module including the major methane chemical reactions, is run to simulate CH4 concentrations and δ13C - CH4 at the global scale. Simulations with and without chlorine chemical sink are performed. Atmospheric methane sink by chlorine atoms in the stratosphere is found to be about 5 Tg/yr. Above 20 km, the presence of chlorine in the model is found to have only a small positive impact on the vertical profile of total methane but a major influence on δ13C values, increasing the agreement between simulations and available observations.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2019
- Bibcode:
- 2019EGUGA..21.2410T