École Nationale Supérieure de
Techniques Avancées

Abstract

Methane (CH 4 ) is the second strongest anthropogenic greenhouse gas after carbon dioxide (CO 2 ) in terms of anthropic contribution. Since the pre-industrial era, its mixing ratio in the atmosphere has increased continuously, reaching 1850 ppb on average in 2018. Better knowledge of its sources and sinks is now essential to design appropriate mitigation policies that aim at reducing greenhouse gas emissions. Numerical models simulations are a key tool for studying those gases. The LMDz-SACS atmospheric chemistry-transport model is able to simulate global methane concentrations. However, the stratospheric chlorine sink was not implemented until now. Direct simulations were performed to estimate its impact on methane modeling. Results show that the stratospheric chlorine sink can be estimated to 5 Tg/yr. The simulated methane vertical profile can differ from the observations between 10 and 20 km above the surface and the chlorine implementation does not totally fix the problem. However, including chlorine improves the comparison. As to the δ 13 C isotopologue fractionation, the chlorine reaction, which is very fractioning, has a positive impact on the results, now more consistent with available observations.