The influence of methane emissions on tropospheric NOx re-cycling

We have investigated the effect of introducing CH4 surface emission estimates on global chemistry transport model simulations of the composition of the global troposphere for the period 2000 to 2009. By applying both the EDGAR and LPJ-WhyMe emission inventories simultaneously, in combination with nudging to surface CH4 observations in the background atmosphere, significant improvements occur in the simulated regional distribution of surface CH4 and in the seasonal cycle compared to surface observations. With the application of
variable surface emissions the burden of tropospheric CH4 is enhanced compared to a simulation with prescribed background surface CH4 concentrations as used traditionally in chemistry transport modelling. This enhanced CH4 burden and spatiotemporal variability in CH4 distribution results in an increase in the chemical production of the peroxy-radicals HO2 and CH3O2, which subsequently increases the efficiency of NOx re-cycling. The net result is a modest increase in the tropospheric burdens of both O3 and CO. These increases are found to have both a seasonal and regional dependency. The simulations demonstrate the complex interrelationship between the global burdens of CH4, tropospheric O3, and CO as well as the chemical feedbacks at play for enhancements and variability in CH4 emissions in the presentday
atmosphere.