This study assesses the influence of anthropogenic emission inventories of ozone (O3) precursor species (i.e. NOx, CO, and non-methane hydrocarbons (NMHCs)) prescribed in the simulations of the two phases of the Chemistry-Climate Model Initiative (CCMI) on tropospheric O3, hydroxyl radical (OH), and the methane (CH4) lifetime. We performed two transient simulations for the period 2000-2010 with the chemistry-climate model EMAC, one prescribing the emission inventory of CCMI-1 and the other that of CCMI-2022. Using the tagging approach, we attribute the differences of O3, OH, and the tropospheric CH4 lifetime to individual emission sectors. It is, to our knowledge, the first application of the tagging approach to attribute changes of the simulated CH4 lifetime to individual emission sectors. The emission inventory used for CCMI-2022 leads to a 3.7 % larger tropospheric O3 column and to a 3.2 % shorter tropospheric CH4 lifetime compared to CCMI-1 in the Northern Hemisphere. In the Southern Hemisphere, the tropospheric O3 column is 4.5 % larger, and the tropospheric CH4 lifetime 4.3 % shorter. Differences in tropospheric O3 are largely driven by changes of emissions from the anthropogenic non-traffic and land transport sectors in the Northern Hemisphere. In the Southern Hemisphere, the primary contributors are emissions from anthropogenic non-traffic, biomass burning, and shipping. These sectors also play a significant role in reducing the simulated tropospheric CH4 lifetime. However, the contribution of a particular sector to changes in O3 does not necessarily align with its impact on the CH4 lifetime.

The chemical sink of atmospheric methane (CH₄) depends on the temperature and on the chemical composition. Here, we assess the feedback on atmospheric CH₄ induced by changes in the chemical sink in a warming climate using a CH₄-emission-flux-driven set-up of the chemistry-climate model EMAC (ECHAM/MESSy Atmospheric Chemistry), in which the chemical feedback of CH₄ mixing ratios can evolve explicitly. We perform idealized perturbation simulations driven either by increased carbon dioxide (CO₂) mixing ratios or by increased CH₄ emission fluxes. The CH₄ emission flux perturbation leads to a large increase of CH₄ mixing ratios. Remarkably, the factor by which the CH₄ mixing ratio increases is larger than the increase factor of the emission flux, because the atmospheric lifetime of CH₄ is extended. In contrast, the individual effect of the global surface air temperature (GSAT) increase is to shorten the CH₄ lifetime, which results in a significant reduction of CH₄ mixing ratios in our set-up. The corresponding radiative feedback is estimated at -0.041 and -0.089 W m^-2 K^-1 for the CO₂ and CH₄ perturbation, respectively. The explicit response of CH₄ mixing ratios leads to secondary feedbacks on the hydroxyl radical (OH) and ozone (O₃). Firstly, the OH response includes the CH₄-OH feedback, which enhances the CH₄ lifetime change, and, secondly, the formation of tropospheric O₃ is reduced.