Atmospheric Physics and Chemistry Group (APCG)


Past Projects

(Inverse) Modeling of CH4 using isotopes

Guillaume Monteil


Methane (CH4) is the second most important greenhouse gas produced by human activity. Its concentrations increased from 400 ppb during the preindustrial period to approximatively 1800 ppb today. However this increase has not been regular. In particular, the concentration remaind almost steady from 1998 to 2006, when they started to increase again.
Those variations are not fully understood yet. There are in particular a lot of uncertainties about changes of natural methane emissions. To understant better the impact of each process on the methane cycle, information can be obtained by looking at methane isotopes, in particular 13CH4.
We use the global atmospheric chemistry-transport models TM3 and TM5 to simulate the study the spatial and temporal evolution of the methane concentrations. We follow mainly two approaches:
- Forward simulations of CH4 and 13CH4 concentrations are ran using the TM3 model, on a very coarse resolution (7.5x10 degrees), and on long time series (~40 years). The objective is to evaluate the capacity of different sources-sinks scenarios to reproduce the observed CH4 and 13CH4 concentrations.
- We use the TM5 model to run inverse simulations of ground based and satellite measurements of CH4 mixing ratio, together with an a priori information on methane fluxes to obtain a best estimate of methane emissions. We focus on the most recent years, when satellite (SCIAMACHY, GOSAT) data are available.